FEMALE MATE CHOICE IN THE DOMESTICATED GOAT (CAPRA
HIRCUS): CURRENT UNDERSTANDINGS AND IMPLICATIONS
by
KRISTY M. LONGPRE
A dissertation submitted to the
Graduate School-New Brunswick
Rutgers, The State University of New Jersey
In partial fulfillment of the requirements
For the degree of
Doctor of Philosophy
Graduate Program in Endocrinology and Animal Biosciences
Written under the direction of
Dr. Larry S. Katz
And approved by
__________________________
__________________________
__________________________
__________________________
__________________________
New Brunswick, New Jersey
JANUARY, 2011
ABSTRACT OF THE DISSERTATION
FEMALE MATE CHOICE IN THE DOMESTICATED GOAT (CAPRA HIRCUS):
CURRENT UNDERSTANDINGS AND IMPLICATIONS
By KRISTY M. LONGPRE
Dissertation Director:
Dr. Larry S. Katz
Female mate choice is the tendency for females to distinguish among and mate
selectively with one specific phenotype. In promiscuous species in which males
contribute genes only, females should mate with higher quality males. This propensity
accounts for the display of dimorphic characteristics that cannot be explained through
Darwin’s theory of natural selection. Female mate choice has not been studied in
domesticated species like the goat, in part due to single-male breeding programs and the
use of artificial insemination which inhibit the opportunity for mate choice. However,
existence of mate choice in a domesticated species would suggest that the underlying
mechanisms of mate choice are robust. Results from a series of experiments support the
concept of mate choice in domestic animals. Female goats are able to distinguish among
and show preference for males with higher testosterone (T) concentrations. Females may
ii
use a suite of T-dependent physiological and behavioral cues that increase in frequency
and intensity during the breeding season to assess potential mates, specifically courtship
and chemical cues. Behavior studies indicate that morphological cues are not used to
distinguish among males. Instead, males that display intense chemical and/or courtship
cues are preferred by estrous females. Analysis of T concentrations reveals that males
with higher T concentrations have more intense chemical cues and higher courtship rates
than those with lower T concentrations. High testosterone concentrations appear to
impose high energetic costs as males with high T concentrations lose more body weight
during breeding season, likely due to the increased frequency of T-dependent
physiological and behavioral cues. Testosterone concentrations and resulting Tdependent behaviors may serve as an honest indicator of a male’s overall fitness.
iii
DEDICATION
I dedicate this to my parents, Darlene and Raymond Skidmore, for giving me a life filled
with love, meaning and purpose.
To my sister Kelly, for the years of advice and perspective which extend beyond that of
any book.
To my nieces Faith and Trinity, for your constant love and continual understanding.
Never forget that anything is possible.
And finally to my extended family (the Clements’, Longpre’s and Raines’, all associated
grandparents, uncles, aunts, cousins) and friends for your love and support.
iv
ACKNOWLEDGEMENTS
I would like to express my most sincere gratitude to my graduate research advisor,
Dr. Larry S. Katz, for his guidance and support throughout my graduate studies. His
contribution to my personal and academic growth these past five years is priceless.
In addition, I would like to thank the members of my committee, Drs. Carol
Bagnell, Linda Rhodes, and my outside committee members Bruce Cushing and Ryne
Palombit.
My deepest appreciation goes out to Susan Becker for her experimental and
organizational advice, teaching me all I know about handling, bleeding and injecting
goats, and her enduring support in the laboratory.
A special thanks to Ms. Laura Comerford, Karin Mezey, Rebecca Potosky and
Mr. Clint Burgher and the undergraduate researchers for your assistance over these past
years, I could not have done it without you.
Finally, to my family, friends and Lola. Thank you for being there whenever I
needed you.
v
TABLE OF CONTENTS
Title
Page #
TITLE PAGE
i
ABSTRACT OF THE DISSERTATION
ii
DEDICATION
iv
ACKNOWLEDGEMENTS
v
TABLE OF CONTENTS
vi
LIST OF TABLES
ix
LIST OF FIGURES
x
CHAPTER I
Review of Literature
A.
The purpose and scope of the literature review
2
B.
Female mate choice in mammals
2
C.
Ornamentation: Coloration and other visual signals
3
D.
Weapons
5
E.
Vocal Display
7
F.
Chemical Cues
8
G.
Courtship Display
11
H.
Testosterone and male characteristics
13
I.
Use of the goat as a model - significance for conservation
15
J.
Hypothesis and predictions
17
K.
References
18
vi
TABLE OF CONTENTS (continued)
Title
Page #
CHAPTER II
Estrous Female Goats Use Testosterone-Dependent Cues to Assess Mates
A.
Abstract
32
B.
Introduction
33
C.
Materials and Methods
37
D.
Results
41
E.
Discussion
43
F.
Table and Figures
49
G.
References
55
CHAPTER III
Female Goats Use Courtship Display as an Honest Indicator of a Male’s Fitness
A.
Abstract
61
B.
Introduction
62
C.
Materials and Methods
66
D.
Results
72
E.
Discussion
74
F.
Figures
79
G.
References
85
CHAPTER IV
Scent of a Buck: Do Males Advertise Fitness Via Olfactory Cues?
A.
Abstract
90
vii
TABLE OF CONTENTS (continued)
Title
Page #
B.
Introduction
92
C.
Materials and Methods
95
D.
Results
101
E.
Discussion
102
F.
Figures
105
G.
References
111
CHAPTER V
The Cost of Maintaining High Testosterone Concentrations: Implications for LifeHistory Trade-Offs
A.
Abstract
117
B.
Introduction
119
C.
Materials and Methods
124
D.
Results
129
E.
Discussion
131
F.
Figures
135
G.
References
140
CHAPTER VI
A.
Dissertation Conclusions
146
B.
References
151
Curriculum Vita
153
viii
LIST OF TABLES
Table #
1.
Title
Female Preference Tests by Experiment
ix
Page #
49
LIST OF FIGURES
Title
Page #
CHAPTER II
Figure 1.
Goat phenotypes
50
Figure 2.
Test apparatus for female mate choice paradigm
51
Figure 3.
Estrous females prefer bucks in the breeding and non-breeding
52
season
Figure 4.
Estrous females prefer TP-treated males regardless of male
53
morphology
Figure 5.
Estrous females prefer males with higher T concentrations at the
54
time of the behavior test
CHAPTER III
Figure 1.
Male courtship rate test apparatus
79
Figure 2.
Test apparatus for female preference test paradigm
80
Figure 3.
Male courtship rate and T concentrations are correlated
81
Figure 4.
Estrous females prefer high courting bucks
82
Figure 5.
Courtship rate and T concentrations for TP-treated Wethers
83
Figure 6.
Estrous female prefer TP-treated Wethers that court at higher
84
rates
CHAPTER IV
Figure 1.
Test apparatus for buck vs wether-scented and control rag
female preference test paradigm
x
105
LIST OF FIGURES (continued)
Title
Figure 2.
Test apparatus for “Near” and “Far” buck-scented rag female
Page #
106
preference test paradigm
Figure 3.
Estrous females prefer buck-scented rags
107
Figure 4.
Serum T concentrations for bucks and wethers
108
Figure 5.
Estrous females prefer Near buck-scented rags
109
Figure 6.
Serum T concentrations for Near and Far bucks
110
Weekly serum T concentrations for Near and Far bucks during
135
CHAPTER V
Figure 1.
the breeding season
Figure 2.
Near bucks have higher serum T concentrations then Far bucks
136
Figure 3.
Placement of Far bucks near females caused an increase in T
137
concentrations
Figure 4.
Weekly serum T concentrations and monthly body weights for
138
six bucks
Figure 5.
Quarterly body weights of TP-treated wethers
xi
139
1
CHAPTER I
REVIEW OF LITERATURE
2
A.
The purpose and scope of literature review
The goal of this research is to determine if domesticated animals, the results of
significant artificial selection pressure as well as the relaxation of some natural selective
pressures, display mate choice. More specifically the female goat (Capra hircus) was
used as a model for the study of female mate choice. Females may use a variety of maletypical characteristics to distinguish among males. There are several mechanisms by
which female choice may operate, however the goal of this review is to introduce
possible characteristics or cues that females may be using to distinguish among males and
to explore a mechanism by which males may regulate the display of these cues.
Implications from this research extend our understanding of mammalian mate choice, and
may aid in reproduction of conserved ungulate species.
B.
Female mate choice in mammals
In The Descent of Man, Darwin (1871) proposed his theory of sexual selection
whereby competition for access to mates drives selection. In a promiscuous species, in
which there is greater maternal investment in the offspring, females should be choosier
and mate exclusively with higher quality males (Trivers, 1972). Males often compete to
gain access to females either directly, by engaging in battles with other males or
indirectly by display of extravagant characteristics that attract females. A female’s ability
to distinguish among and mate with high quality males is a major determinant of her
reproductive success (Krebs and Davies, 1978). Females may use a variety of attributes
to evaluate and distinguish amongst males; often preferring males with extravagant
secondary sexual characteristics (reviewed in: Andersson, 1994). Sexual selection
theories suggest that extravagant characteristics may predispose males to predation and
3
are often costly to produce and maintain, preventing low quality males from displaying
and/or maintaining a high expression of secondary sexual characteristics (Zahavi, 1975).
Thus, display of such extravagant characteristics may serve as an honest indicator of a
male’s fitness.
The study of female mate choice in large mammals is limited. This is in large due
to the fact that in mammals, males are usually the larger sex (Ralls, 1976) and have large
weaponry such as horns and antlers, compared to that of females (Clutton-Brock, 1977;
Clutton-Brock and Harvey, 1978; Leutenegger and Kelly, 1977; Lincoln, 1994). Such
male-typical characteristics make the notion of female mate choice seem irrelevant in
mammals as females could be easily injured or dominated by a male. However, a
growing body of research suggests that females mate preferentially with males displaying
particular characteristics including ornamentation, weaponry, vocal displays, chemical
cues and courtship displays. Females may be mating with males displaying such
characteristics for a variety of processes, one of which is female choice. These
characteristics may provide females with the ability to distinguish among and mate
selectively with high quality males. Thus, females may gain genetic benefits by mating
with males displaying such traits (Norris, 1993; Petrie, 1994; Sheldon et al., 1997).
C.
Ornamentation: Coloration and other visual signals
Studies examining the function of conspicuous colors and ornamentation, often in
birds and fish, have been important to the development of current understandings of
female mate choice. Male coloration is often used by females to assess male quality.
Female fish (Kodric-Brown, 1985; 1989) and birds (Blount et al., 2003; Hill, 1990;
1991) use male carotenoid-based coloration to distinguish among and mate selectively
4
with brightly colored males. Bright carotenoid-based coloration may serve as an honest
signal of male quality since males must ingest carotenoids in order to express the
coloration and environmental carotenoid availability is limited (Grether et al., 1999)
allowing only high quality males to express extravagant coloration. Studies have found
that carotenoid-based coloration reflects nutritional condition (Hill, 1992; Hill and
Montgomerie, 1994) and disease resistance (Houde and Torio, 1992; Milinski and
Bakker, 1990; Thompson et al., 1997).
Exaggerated morphological ornaments may serve to attract females. Male birds
with longer tail ornaments are often preferred by females (Andersson, 1982; Møller,
1988; Pryke et al., 2001; Smith and Montgomerie, 1991). Male barn swallows with long
tail feathers had more offspring in extra-pair broods (Kleven et al., 2006; Saino et al.,
1997). The size of tail ornaments reflect a male’s age (Manning, 1985), and quality as
high quality males are predicted to have increased survivability. Studies have found that
there is a negative correlation between tail length and parental care (Qvarnstroöm, 1997;
Winquist and Lemon, 1994), suggesting that females that mate with males with long tail
ornaments benefit indirectly by obtaining “good” genes (Kirkpatrick, 1996). Similarly,
males with longer spurs were preferred by female pheasants (von Schantz et al., 1994).
Although male spurs may appear to aid in male-male competition, they show no
correlation to male dominance or territory quality. Instead, the spur length was found to
be correlated with male survivability and number of offspring produced (von Schantz et
al., 1994); thus also likely serving as an indicator of male quality.
In mammals, many primates display conspicuous coloration on their face, rump
and genitals, referred to as “sexual skin” (Dixson, 1983). Studies have found a correlation
5
between male sexual skin intensity and male status in rhesus macaques (Waitt et al.,
2003), gelada baboons (Bergman et al., 2009), and vervet monkeys (Gartlan and Brain,
1968). Setchell (2005) found that brightness of the male coloration was found to
positively correlate with proximity to, sexual presentations received by, and approaches
accepted by the females, suggesting that male coloration is important factor influencing
mate choice. The color, specifically darkness, of lion manes vary among males. West and
Packer (2002) found that darkness of the lion mane is an honest indicator of male quality,
status and testosterone concentrations. Males with dark manes are preferred by females,
avoided by males, have longer reproductive life-spans and higher offspring survival. Due
to the dark coloring of the male mane, males are often hotter, with higher surface
temperatures compared to lighter mane males or females. Coloration may also change
depending on male quality. During periods of poor nutrition, blue genital coloration of
vervet monkeys fades (Isbell, 1995). Coloration may reliably indicate parasite resistance
(Hamilton and Zuk, 1982), with brighter males displaying lower parasite load. Bright
coloration was found to be associated with high concentrations of testosterone in
Mandrills (Setchell and Dixson, 2001; Wickings, 1993). High T concentrations have been
shown to negatively affect a male’s health by causing immune suppression (Grossman,
1984; Marsh and Scanes, 1994; Mougeot et al., 2004; Peters, 2000). Thus, T-dependent
male coloration may accurately reflect a male’s health condition.
D.
Weapons
Male birds possess wing and leg spurs which may be used as weapons. Of the
species with spurs, a majority are polygynous (Davison, 1985), suggesting that spurs may
6
also be used to attract females. Spur length in the ring neck pheasant was correlated with
dominance in adults and also correlated with other female preferred characteristics,
including wattle display (Mateos and Carranza, 1996), thus, female preference is not
based on spur length, but other associated traits. Von Schantz et al. (1997) found that spur
length of ring-necked pheasants was preferred by females and correlated to male age and
condition. Further, change in spur length between two reproductive seasons was an
accurate predictor of male life expectancy as spur length was longer for males that were
older, and survived, than for males that did not survive. Thus, spur length is an honest
condition-dependent ornament.
Weapons such as canine teeth, antlers, and horns are characteristics that may be
used as weapons against attack by competing males or predators or attract females
(reviewed in: Andersson, 1994). Phylogenetic analysis of canine tooth dimorphism in
primates revealed that in more polygynous species, larger canines are more prevalent and
is allometrically correlated with body size (Thoren et al., 2006), possibly serving to
attract mates or challenge males. Studies in which antlers were removed from male
reindeer and red deer, dominance status and fighting ability was reduced (Clutton-Brock,
1982; Kruuk et al., 2002; Suttie, 1980), likely because antlers aid in male-male
competition over females. Further, Bartoš and Bahbouh (2006) demonstrated that the
probability of a male becoming a harem holder was correlated to antler size and
branching. Malo et al. (2005) found that antler size was associated with male fertility,
specifically testes size, and sperm production and sperm velocity. Antler and horn size in
male ungulates are often correlated with male age, body size, fighting ability and mating
success (Clutton-Brock, 1982; Coltman et al., 2002; Geist, 1974; Kruuk et al., 2002).
7
Such age-dependent characteristics may be an honest indicator of genetic quality, and
good genes may account for the increased survivability of older males (Kokko, 1997;
Kokko and LindstrÖm, 1996), thus in mating with older males with larger antlers or
horns, females stand to benefit from these good genes by passing them on to their
offspring.
E.
Vocal Display
Male reproductive vocal displays are sexually selected characteristics. During the
breeding season, male mate success is often dependent on song for a number of birds.
Male repertoire size (Buchanan and Catchpole, 1997; Reid et al., 2004; Searcy and
Yasukawa, 1996; Vallet et al., 1998), number of song bouts (Gentner and Hulse, 2000) or
strophe length (Martín-Vivaldi et al., 1999) are all characteristics used by females during
mate selection. Frequency of male song may be constrained by body size (Genevois and
Bretagnolle, 1994; Ryan and Brenowitz, 1985). Singing may impose a cost to males.
Predators can locate their prey by using their song; increasing predation risks to males
singing (Mougeot and Bretagnolle, 2000). Time that male canaries spent singing caused a
proportional increase basal metabolic rate (BMI) (Ward et al., 2003). Both male
nightingales (Thomas, 2002) and canaries (Ward et al., 2003) engaging in dawn chorus
increased their BMI substantially compared to those that were roosting, suggesting that
the time of day that a male sings is an indication of male quality. Further, male singing
activity is usually isolated to the breeding season when T concentrations are high (Ball
and Balthazart, 2004; Ketterson et al., 1991). Due to the immunosuppressive effects of
high T concentrations, high T concentrations may, in turn, negatively impact the
expression of male song (Folstad and Karter, 1992; Peters, 2000).
8
Vocalization displays are also prevalent among amphibians and reptiles. Female
selection for specific aspects of a male song, specifically song complexity, has led to the
divergence and subsequent speciation of Amazonian frog, P. petersi (Boul et al., 2007).
Male grey tree frogs displaying long calls sired offspring with higher phenotypic quality
(Welch et al., 1998), thus, successful fathers sired successful sons. During mounting,
male marginated tortoises emit calls which are related to a male’s mating success, body
weight and carapace shape (Sacchi et al., 2003). Galeotti et al. (2005) found that female
Hermann’s tortoises prefer males with fast rate, high pitched mounting calls, which likely
provide information about male quality.
In mammals, male red-deer stags roar. Roaring of males has been shown to
advance the time of estrus (McComb, 1987). Male roaring rate is positively associated
with male fighting ability (Clutton-Brock and Albon, 1979) and mating success
(McComb, 1991). Males competing and winning contests are likely high quality, and
should be preferred by females. Older, larger males were found to have lower format
frequencies in their roars (Reby and McComb, 2003), possibly providing reliable
information about their size, age and experience to potential opponents or females. In
call-back experiments, Charlton et al. (2007) found that females approached speakers
producing roars simulating larger males. Females are able to use vocal cues to distinguish
among and mate preferentially with high quality males.
F.
Chemical Cues
Chemical cues are a common form of communication for most species. As such,
there is an expansive amount of research that has been conducted on chemical
components and function of chemical cues for species including insects, fish, amphibians
9
reptiles and some mammals, specifically rodents (reviewed in: Johansson and Jones,
2007; Wyatt, 2003). Due to the breadth of knowledge, this section of the literature review
will only focus on chemical cues with respect to female mate choice, with an emphasis on
mammalian mate choice.
Chemical cues are important for mammalian reproduction and may aid in mate
choice. Exposure of females to male chemical cues induces female arousal and mating
behavior (Keverne, 1977). Chemical cues may act as primer pheromones. Several rodent
studies have found that exposing female mice to male chemical cues accelerates puberty
(Colby and Vandenberg, 1974; Kaneko et al., 1980; MacIntosh Schellinck et al., 1993).
Further, ovulation frequencies increase upon exposure to male chemical cues in moose
(Bowyer et al., 1994; Miquelle, 1991) and goats (Coblentz, 1976; Gelez et al., 2004;
Gelez and Fabre-Nys, 2006; Walkden-Brown et al., 1993a). Females are able to use
chemical cues to distinguish among males. Female rodents prefer scent marks from intact
versus castrated males (Carr et al., 1965), dominant males (Drickamer, 1992; Gad, 1990;
Gosling and Roberts, 2001b; Horne and Ylonen, 1996; Mossman and Drickamer, 1996),
and prefer odors from males with a lower quantity or no parasits (Kavaliers and Colwell,
1993; Kavaliers and Colwell, 1995; Penn and Potts, 1998; Rantala et al., 2002; Zula et
al., 2004). In pigs, estrous females are attracted to male saliva (Melrose et al., 1971).
Rasmussen and Schulte (1998) found that estrous Asian and African elephants are
attracted to urine from males in musth. Female moose and bison are attracted to wallows
of dominant males (Bowyer et al., 2007; Bowyer et al., 1998; Whittle et al., 2000). It is
possible that the same chemical cues which act as primer pheromones, also aid in female
mate choice.
10
Chemical cues provided within scent marks are also informative to potential
mates or competitors. They are species specific and are a direct and labile characteristic.
Studies have shown that chemical cues are reliable indicators of nutritional condition
(Ferkin et al., 1997; Fisher and Rosenthal, 2006; Olsen et al., 2003; Opuch and Radwan,
2009), health (Lopez et al., 2006; Penn and Potts, 1998; Penn et al., 1998), and
dominance status (Carazo et al., 2004; Gosling and Roberts, 2001a; Rasmussen et al.,
2002; Schneider et al., 2001; Schneider et al., 1999). Male rodents that scent mark or
over-mark areas or themselves at a high frequency are preferred by females (Gosling et
al., 2000b; Rich and Hurst, 1998; Rich and Hurst, 1999; Roberts, 2007). Thus, males may
benefit from scent marking by increasing their attractiveness. Frequency of scent marking
and chemical cues within scent marks have been shown to be heritable for rodents (Horne
and Ylönen, 1998; Roberts and Gosling, 2003) and deer (Johansson and Jones, 2007;
Lawson et al., 2000;), thus females that mate with high quality males may increase
indirect benefits.
Scent marking and production of chemical cues is costly. Scent marking provides
both potential competitors and females with the ability to assess a male when he is no
longer present. Accordingly, maintenance of scent marks is critical for maintenance of
status. Brashares and Arcese (1999) found that African antelope males may spend
upwards of 35% of their time scent marking or engaging in associated behaviors, which
results in less time foraging for food. Male scent marking rate was negatively correlated
with growth rate and asymptotic body size in house mice (Gosling et al., 2000a).
Predation risks also increase with scent marking (Koivula and Korpimaki, 2001). Due to
11
the high costs associated with scent marking, high frequency scent marking may be an
honest indicator of a male’s fitness.
G.
Courtship Display
Often times adornments, bright coloration, and extravagant displays are all
defined as characteristics of courtship (reviewed in: Andersson, 1994). However,
adornments and bright coloration may serve as indicators of male quality themselves
(refer to section C), or enhance and increase attraction to the male courtship display
(McLintock and Uetz, 1996). The focus of this section of the literature review will be on
male courtship display behaviors.
Male courtship behavior may be important for female reproductive behavior. In
birds, rearing females with males or with visual contact to males accelerated sexual
maturation (Widowski et al., 1998) and enhanced mating success (Leonard et al., 1993).
Barfield (1971) found that female reproductive development was correlated with length
of exposure to and courtship behavior displayed by courting males. Further, egg
production was higher in females with visual contact to male turkeys compared to egg
production of females with no contact to males (Jones and Leighton Jr, 1987). For
salamanders, courtship display is necessary for females to become receptive (Halliday,
1990). In mammals, Perkins and Fitzgerald (1994) found that male rams exhibiting high
sexual performance also courted females more than those that were low sexual
performers. Females that were housed with a high performing ram ovulated earlier and
exhibited associated sexual behaviors while females housed with a lower performing ram
had short estrous cycles characterized by early progesterone peaks, but no associated
sexual behavior. In addition, sexual performance in the ram is heritable (Snowder et al.,
12
2002). High quality, courting males may stimulate female reproductive behaviors,
increasing the likelihood that females will mate exclusively with high quality males.
Male courtship displays may also be a quality used by females to assess males.
Specific characters of interest include courtship rate, frequency and duration. Females use
male courtship rate to distinguish among males. Jiguet and Bretagnolle (2001) found that
little bustard males display wing flashes and jumps only performed in the presence of
females. Due to the observed high variations in display rate among males but minimal
differences in individual display rate, it suggests that wing flash and jump display may be
an indicator of male quality. High frequency wing displays were also preferred
characteristic among female domestic chickens (Leonard and Zanette, 1998). Male sage
grouse perform a highly stereotyped strut which consists of both acoustic and visual
courtship display components. Male strut rates are highest when females are on or near a
males territory (Gibson and Bradbury, 1985), suggesting that courtship rate is used for
female mate choice.
Frequency and duration of courtship display may serve as an important indicator
of male quality. Karino (1995) found that courtship frequency, over male size, was most
important for female mate preference for two species of damselfish. Vinnedge and
Verrell (1998) found that male salamanders that had higher courtship frequency generally
had higher mating success. Male fiddler crabs often display a claw wave, consisting of an
upstroke, pause then downstroke, to attract females. Males that were visited by females
had a shorter duration between the upstroke and downstroke of the wave and waved their
claw higher (Murai and Backwell, 2006). In the dark-eyed junco, males who received
13
testosterone implants out-performed control males in a variety of courtship displays and
high courting males were preferred by females (Enstrom et al., 1997).
Courtship display is costly to perform. Vehrencamp et al. (1989) found that
energy expenditure increased with male display rate, and male dark-eyed juncos
attending leks and performing struts were in better body condition then those not
attending. Males attending leks were able to overcome the costs associated with courting
females. Casto et al. (2001) found that courting rate in the dark-eyed junco was correlated
with T concentrations. Further, males with T implants during the breeding and nonbreeding season had increased susceptibility to disease and parasitic infection, suggesting
that males with high T concentrations have increased susceptibility to disease and
immune suppression. Males that court at high rates are able to avoid the costs associated
with high circulating T concentrations. Males engaging in courtship behaviors are unable
to simultaneously forage or hunt for food (Gaunt et al., 1996; Mainguy and Côté, 2008;
Marler and Moore, 1989; Wolff, 1998), leading to increased body mass loss. Courtship
likely serves as an honest indicator of male fitness, and females mating with high
courting males gain indirect benefits.
H.
Testosterone and male characteristics
Testosterone is a well studied hormone and its physiological actions and effects
have been well characterized (reviewed in: Grossman, 1984; Hau, 2007; Rhen and
Crews, 2002; Wilson et al., 1981). Testosterone is a hormone secreted primarily by the
testes. T production is regulated by the hypothalamus and anterior pituitary gland. In
response to a stimulus (low circulating testosterone levels), the hypothalamus releases
gonadotropin-releasing hormone (GnRH), which in turn stimulates the anterior pituitary
14
to release luteinizing hormone (LH) and follicle stimulating hormone (FSH). Both LH
and FSH stimulate the testes to secrete T into systematic circulation, eliciting
physiological and behavioral responses. Testosterone production may be stimulated by
photoperiod (Blottner et al., 1996; Delgadillo et al., 2004; Martins et al., 2006; WalkdenBrown et al., 1994a; Walkden-Brown et al., 1994b; Yang et al., 1998), presence of
females (Graham and Desjardins, 1980; Illius et al., 1976; Purvis and Haynes, 1974; van
der Meij et al., 2008; Walkden-Brown et al., 1999), or presence of other males (Albert et
al., 1990; Harding and Follett, 1979; Pinxten et al., 2003; Ramenofsky, 1984; Steklis et
al., 1985; Wingfield, 1985).
Testosterone is important for the expression of reproductive behaviors including
aggression (Albert et al., 1990; Cavigelli and Pereira, 2000; Marler and Moore, 1988;
Marler and Moore, 1989; McGlothlin et al., 2008; Wingfield et al., 1987), courtship
(Damassa et al., 1977; Fusani, 2008; Fusani et al., 2007; Fusani and Hutchison, 2003;
Wiley and Goldizen, 2003), vocalizations (Fusani et al., 1994; Nespor et al., 1996; Nunez
and Tan, 1984; Wada, 1986) and chemical signaling (Arteaga et al., 2008; Jainudeen et
al., 1972; Miller et al., 1987; Yahr and Thiessen, 1972). Castration prior to puberty often
results in males displaying a deficit of T-dependent characteristics while males castrated
post-pubertally show an initial decrease and an eventual loss in reproductive behaviors
(Adkins-Regan, 1981; Costantini et al., 2007; D'Occhio and Brooks, 1980; D'Occhio and
Brooks, 1982; Damassa et al., 1977; Davidson, 1966; Hart and Jones, 1975). Testosterone
replacement can restore these characteristics similar to the level of an intact male during
the breeding season (Arnold, 1975; Beach and Pauker, 1949; Clegg et al., 1969; Foote et
al., 1977; McGinnis et al., 1989; Yahr et al., 1979; Young et al., 1964).
15
Maintaining high T concentrations is costly for a male. In both avian and reptilian
species, studies have shown that high T concentrations decrease survivability (Dufty,
1989; Ketterson et al., 1996; Marler and Moore, 1988), causing immune suppression
(Belliure et al., 2004; Duffy et al., 2000; Grossman, 1984; Marsh and Scanes, 1994;
Mougeot et al., 2004; Peters, 2000), and increasing energetic costs through increasing
metabolic rate (Buchanan et al., 2001; Ryser, 1989) and increasing the loss of fat reserves
(Ketterson et al., 1991; Wingfield, 1984). Further, the display of T-dependent secondary
sexual characteristics and behaviors is energetically costly and males engaging in such
behaviors are unable to simultaneously forage or hunt for food (Gaunt et al., 1996;
Mainguy and Côté, 2008; Marler and Moore, 1989; Wolff, 1998), leading to decreased
body weights.
I.
Use of the goat as a model - significance for sexual selection
Goats provide an excellent model for examining mate choice and reproductive
behaviors. The goat is one of the oldest domesticated species and has been bred for meat
and milk production for thousands of years (Zeuner, 1963). Single sire breeding is often
used by farmers in which one male is introduced into a herd of females for the duration of
the breeding season. He is the sole sire of all offspring, which makes the goat seem like
an unconventional model for displaying mate choice. However, goats are promiscuous
and offspring care is maternal only so they meet the criteria for displaying mate choice
(Trivers, 1972). Existence of mate choice in a domesticated species such as the goat
suggests that the underlying mechanisms of mate choice are robust as artificial selection
pressures and adaptation to the domestic environment have not overcome the strength of
sexual selection of the species. These underlying mechanisms may be similar to that of
16
other ungulate species, making the goat and excellent model for the study of mate choice
for other less accessible ungulate species.
Similar to other ungulate species, goats exhibit a large fluctuation in behavioral
expression between the breeding and non-breeding seasons (Geist, 1974; Walther, 1984).
During the breeding season, when T concentrations are high (Grasselli et al., 1992;
Muduuli et al., 1979; Walkden-Brown et al., 1994b), intensity of chemical cues provided
by the male is high. Male goats urinate on their front legs and beards, almost exclusively
during the breeding season (Coblentz, 1976; Walther, 1984). This scent marking behavior
is referred to as scent-urination (Coblentz, 1976) or self-enurination (Price et al., 1986).
In addition to or enhancing chemical cues provided by self-enurination, sebaceous glands
increase in size and chemical composition of glandular secretions change (Coblentz,
1976; Delgadillo et al., 2004; Price et al., 1986) during the breeding season. Iwata et al.
(2000) and Iwata et al. (2001) found that pheromone activity increased when castrated
males were implanted with T capsules and pheromone activity ceased upon removal of
the T capsules, suggesting that chemical cues are T-dependent.
Chemical cues provided by the male during the breeding season have been shown
to induce ovulation. The “male effect” is a well described phenomenon in sheep and
goats, whereby placing a male or his hair near a group of anestrous females will hasten
the onset of seasonal reproductive cyclicity and estrous synchronize the females
(Delgadillo et al., 2006; Delgadillo et al., 2009; Gelez and Fabre-Nys, 2004; 2006;
Hamada et al., 1996; Walkden-Brown et al., 1993b). Although it has been theorized that
the “male effect” evolved to avoid asynchrony of females in the wild (Walkden-Brown et
al., 1999), it is also equally possible that chemical cues provided by the male serve as an
17
honest indicator of fitness that females use to distinguish among males. Thus, upon
detection of a high quality male, females may ovulate.
Male goats also display courtship behaviors during the breeding season. Male
courtship behaviors in goats consist of a head-twist and nudge, tongue flick, and foreleg
kick, which are common courtship traits among ungulates (reviewed in: Walther, 1984).
Courtship is almost exclusively displayed during the breeding season when T
concentrations are high, suggesting that it may be a T-dependent characteristic. Although
little is known about mammalian courtship, examination of courtship behavior in other
species (refer to section G) suggest that it may serve as an honest indicator of fitness.
J.
Hypothesis and predictions
The hypothesis to be tested through research described herein is that the female
domesticated goat (Capra hircus) is an excellent ungulate model for the study of female
mate choice. A number of studies suggest that females mate preferentially with males
displaying particular characteristics. Female preference and mechanism of regulation for
three different male-typical characteristics, commonly displayed among ungulates, were
examined, including morphology, chemical cues and courtship displays. It is predicted
that females will choose among males using some combination of chemical and
behavioral signals to make an assessment. Further it is predicted that males with higher
circulating concentrations of testosterone will be preferred over males with lower
concentrations.
18
K.
References
Adkins-Regan, E., 1981. Effect of sex steroids on the reproductive behavior of castrated
male ring doves (Streptopelia sp.). Physiol Behav. 26, 561-565.
Albert, D. J., Jonik, R. H., Watson, N. V., Gorzalka, B. B., and Walsh, M. L., 1990.
Hormone-dependent aggression in male rats is proportional to serum testosterone
concentration but sexual behavior is not. Physiol Behav. 48, 409-416.
Andersson, M., 1982. Female choice selects for extreme tail length in a widowbird.
Nature. 299, 818-820.
Andersson, M., 1994. Sexual Selection. Princeton University Press, Princeton.
Arnold, A. P., 1975. The effects of castration and androgen replacement on song,
courtship, and aggression in zebra finches (Poephila guttata). J Exp Zool. 191,
309-325.
Arteaga, L., Bautista, A., Martinez-Gomez, M., Nicolas, L., and Hudson, R., 2008. Scent
marking, dominance and serum testosterone levels in male domestic rabbits.
Physiol Behav. 94, 510-5.
Ball, G. F., and Balthazart, J., 2004. Hormonal regulation of brain circuits mediating
male sexual behavior in birds. Physiol Behav. 83, 329-346.
Barfield, R. J., 1971. Gonadotrophic hormone secretion in the female ring dove in
response to visual and auditory stimulation by the male. J Endocrinol. 49, 305.
Bartoš, L., and Bahbouh, R., 2006. Antler size and fluctuating asymmetry in red deer
(Cervus elaphus) stags and probability of becoming a harem holder in rut. Biol J
Linn Soc. 87, 59-68.
Beach, F. A., and Pauker, R. S., 1949. Effects of castration and subsequent androgen
administration upon mating behavior in the male hamster (Cricetus auratus).
Endocrinology. 45, 211-21.
Belliure, J., Smith, L., and Sorci, G., 2004. Effect of testosterone on T cell mediated
immunity in two species of mediterranean lacertid lizards. J Exp Zool Part A. 301,
411-418.
Bergman, T. J., Ho, L., and Beehner, J. C., 2009. Chest color and social status in male
geladas (Theropithecus gelada). Int J Primatol. 30, 791-806.
Blottner, S., Hingst, O., and Meyer, H. H. D., 1996. Seasonal spermatogenesis and
testosterone production in roe deer (Capreolus capreolus). Reproduction. 108,
299.
Blount, J. D., Metcalfe, N. B., Birkhead, T. R., and Surai, P. F., 2003. Carotenoid
modulation of immune function and sexual attractiveness in zebra finches.
Science. 300, 125.
Boul, K. E., Chris Funk, W., Darst, C. R., Cannatella, D. C., and Ryan, M. J., 2007.
Sexual selection drives speciation in an Amazonian frog. Proc R Soc B. 274, 399406.
Bowyer, R. T., Ballenberghe, V. V., and Rock, K. R., 1994. Scent marking by Alaskan
moose: characteristics and spatial distribution of rubbed trees. Can J Zool. 72,
2186-2192.
Bowyer, R. T., Bleich, V. C., Manteca, X., Whiting, J. C., and Stewart, K. M., 2007.
Sociality, mate choice, and timing of mating in American bison (Bison bison):
effects of large males. Ethology. 113, 1048-1060.
19
Bowyer, R. T., Manteca, X., and Hoymork, A. 1998. Scent marking in American bison:
morphological and spatial characteristics of wallows and rubbed trees, pp. 81-91.
In L. R. Irby and J.E. Knight (eds.). International Symposium on Bison Ecology in
North America. Bozeman, Montana.
Brashares, J. S., and Arcese, P., 1999. Scent marking in a territorial African antelope: I.
The maintenance of borders between male oribi. Anim Behav. 57, 1-10.
Buchanan, K. L., and Catchpole, C. K., 1997. Female choice in the sedge warbler
Acrocephalus schoenobaenus: multiple cues from song and territory quality. Proc
R Soc B. 264, 521-526.
Buchanan, K. L., Evans, M. R., Goldsmith, A. R., Byrant, D. M., and Rowe, L. V., 2001.
Testosterone influences basal metabolic rate in male house sparrows: a new cost
of dominance signaling? Proc R Soc B. 268, 1337-1344.
Caillaud, D., Levrero, F., Gatti, S., Menard, N., and Raymond, M., 2008. Influence of
male morphology on male mating status and behavior during interunit encounters
in western lowland gorillas. Am J Phys Anthropol. 135, 379-88.
Carazo, P., Sanchez, E., Font, E., and Desfilis, E., 2004. Chemosensory cues allow male
Tenebrio molitor beetles to assess the reproductive status of potential mates.
Anim Behav. 68, 123-129.
Carr, W. J., Loeb, L. S., and Dissinger, M. L., 1965. Responses of Rats to Sex Odors. J
Comp Physiol Psychol. 59, 370-7.
Casto, J. M., Nolan Jr, V., and Ketterson, E. D., 2001. Steroid hormones and immune
function: experimental studies in wild and captive dark-eyed juncos (Junco
hyemalis). Am Nat. 157, 408-420.
Cavigelli, S. A., and Pereira, M. E., 2000. Mating season aggression and fecal
testosterone levels in male ring-tailed lemurs (Lemur catta). Horm Behav. 37,
246-55.
Charlton, B. D., Reby, D., and McComb, K., 2007. Female red deer prefer the roars of
larger males. Biol Lett- UK. 3, 382-385.
Clegg, M. T., Beamer, W., and Bermant, G., 1969. Copulatory behaviour of the ram,
Ovis aries. III: Effects of pre- and postpubertal castration and androgen
replacement therapy. Anim Behav. 17, 712-717.
Clutton-Brock, T. H., 1977. Sexual dimorphism, socionomic sex ratio and body weight in
primates. Nature. 269, 797-800.
Clutton-Brock, T. H., 1982. The functions of antlers. Behaviour. 79, 108-125.
Clutton-Brock, T. H., and Albon, S. D., 1979. The roaring of red deer and the evolution
of honest advertisement. Behaviour. 69, 145-170.
Clutton-Brock, T. H., and Harvey, P. H., 1978. Mammals, resources and reproductive
strategies. Nature. 273, 191-195.
Coblentz, B. E., 1976. Functions of scent-urination in ungulates with special reference to
feral goats (Capra hircus L.). Am Nat. 110, 549-557.
Colby, D. R., and Vandenberg, J. G., 1974. Regulatory effects of urinary pheromones on
puberty in the mouse. Biol Reprod. 11, 268.
Coltman, D. W., Festa-Bianchet, M., Jorgenson, J. T., and Strobeck, C., 2002. Agedependent sexual selection in bighorn rams. Proc Roy Soc Lond B. 269, 165-.172
20
Costantini, R. M., Park, J. H., Beery, A. K., Paul, M. J., Ko, J. J., and Zucker, I., 2007.
Post-castration retention of reproductive behavior and olfactory preferences in
male Siberian hamsters: role of prior experience. Horm and Behav. 51, 149-155.
D'Occhio, M. J., and Brooks, D. E., 1980. Effects of androgenic and oestrogenic
hormones on mating behaviour in rams castrated before or after puberty. J
Endocrinol. 86, 403-411.
D'Occhio, M. J., and Brooks, D. E., 1982. Threshold of plasma testosterone required for
normal mating activity in male sheep. Horm Behav. 16, 383-394.
Damassa, D. A., Smith, E. R., Tennent, B., and Davidson, J. M., 1977. The relationship
between circulating testosterone levels and male sexual behavior in rats. Horm
Behav. 8, 275-86.
Darwin, C., 1871. The descent of man, and selection in relation to sex. J. Murray,
London.
Davidson, J. M., 1966. Characteristics of sex behaviour in male rats following castration.
An Behav. 14, 266-272.
Davison, G. W. H., 1985. Avian spurs. Journal of Zoology. 206, 353-366.
Delgadillo, J. A., Cortez, M. E., Duarte, G., Chemineau, P., and Malpaux, B., 2004.
Evidence that the photoperiod controls the annual changes in testosterone
secretion, testicular and body weight in subtropical male goats. Reprod Nutr Dev.
44, 183-193.
Delgadillo, J. A., Flores, J. A., Veliz, F. G., Duarte, G., Vielma, J., Hernandez, H.,
and Fernandez, I. G., 2006. Importance of the signals provided by the buck for the
success of the male effect in goats. Reprod Nutr Dev. 46, 391-400.
Delgadillo, J. A., Gelez, H., Ungerfeld, R., Hawken, P. A., and Martin, G. B., 2009. The
'male effect' in sheep and goats--revisiting the dogmas. Behav Brain Res. 200,
304-314.
Dixson, A. F., 1983. Observations on the evolution and behavioral significance of
“sexual skin” in female primates. Adv Stud Behav. 13, 63-106.
Drickamer, L. C., 1992. Oestrous female house mice discriminate dominant from
subordinate males and sons of dominant from sons of subordinate males by odour
cues. Anim Behav. 43, 868-870.
Duffy, D. L., Bentley, G. E., Drazen, D. L., and Ball, G. F., 2000. Effects of testosterone
on cell-mediated and humoral immunity in non-breeding adult European starlings.
Behav Ecol. 11, 654-662.
Dufty, A. M., 1989. Testosterone and survival. Horm. Behav. 23, 185-193.
Enstrom, D. A., Ketterson, E. D., and Nolan Jr., V., 1997. Testosterone and mate choice
in the dark-eyed junco. Anim Behav. 54, 1135-1146.
Ferkin, M. H., Sorokin, E. S., Johnston, R. E., and Lee, C. J., 1997. Attractiveness of
scents varies with protein content of the diet in meadow voles* 1. Anim Behav.
53, 133-141.
Fisher, H. S., and Rosenthal, G. G., 2006. Female swordtail fish use chemical cues to
select well-fed mates. Anim Behav. 72, 721-725.
Folstad, I., and Karter, A. J., 1992. Parasites, bright males, and the immunocompetence
handicap. Am Nat. 139, 603.
21
Foote, R. H., Draddy, P. J., Breite, M., and Oltenacu, E. A., 1977. Action of androgen
and estrone implants on sexual behavior and reproductive organs of castrated
male rabbits. Horm Behav. 9, 57-68.
Fusani, L., 2008. Testosterone control of male courtship in birds. Horm Behav. 54, 227233.
Fusani, L., Beani, L., and Dessi-Fulgheri, F., 1994. Testosterone affects the acoustic
structure of the male call in the grey partridge (Perdix perdix). Behaviour, 128. 3,
301-310.
Fusani, L., Day, L. B., Canoine, V., Reinemann, D., Hernandez, E., and Schlinger, B. A.,
2007. Androgen and the elaborate courtship behavior of a tropical lekking bird.
Horm Behav. 51, 62-68.
Fusani, L., and Hutchison, J. B., 2003. Lack of changes in the courtship behaviour of
male ring doves after testosterone treatment. Ethol Ecol Evol. 15, 143-157.
Gad, S. C., 1990. Recent developments in replacing, reducing, and refining animal use in
toxicologic research and testing. Fund Appl Toxicol. 15, 8-16.
Galeotti, P., Sacchi, R., Fasola, M., Rosa, D. P., Marchesi, M., and Ballasina, D., 2005.
Courtship displays and mounting calls are honest, condition-dependent signals
that influence mounting success in Hermann's tortoises. Can J Zool. 83, 13061313.
Gartlan, J. S., and Brain, C. K., 1968. Ecology and social variability in Cercopithecus
aethiops and C. mitis. pp 253–292. In P.C. Jay (ed.). Primates: Studies in
adaptation and variability. New York, Holt.
Gaunt, A. S., Bucher, T. L., Gaunt, S. L. L., and Baptista, L. F., 1996. Is singing costly?
Auk. 113, 718-721.
Geist, V., 1974. On the relationship of social evolution and ecology in ungulates. Am
Zool. 14, 205-220.
Gelez, H., Archer, E., Chesneau, D., Campan, R., and Fabre-Nys, C., 2004. Importance
of learning in the response of ewes to male odor. Chem Senses. 29, 555-63.
Gelez, H., and Fabre-Nys, C., 2004. The "male effect" in sheep and goats: A review of
the respective roles of the two olfactory systems. Horm Behav. 46, 257-271.
Gelez, H., and Fabre-Nys, C., 2006. Role of the olfactory systems and importance of
learning in the ewes' response to rams or their odors. Reprod Nutr Dev. 46, 40115.
Genevois, F., and Bretagnolle, V., 1994. Male blue petrels reveal their body mass when
calling. Ethol Ecol Evol. 6, 377-383.
Gentner, T. Q., and Hulse, S. H., 2000. Female European starling preference and choice
for variation in conspecific male song. Anim Behav. 59, 443-458.
Gibson, R. M., and Bradbury, J. W., 1985. Sexual selection in lekking sage grouse:
phenotypic correlates of male mating success. Behav Ecol Sociobiol. 18, 117-123.
Gosling, L. M., and Roberts, S. C., 2001a. Scent-marking by male mammals: cheat-proof
signals to competitors and mates. Adv Stud Behav. 30, 169-218.
Gosling, L. M., and Roberts, S. C., 2001b. Testing ideas about the function of scent
marks in territories from spatial patterns. Anim Behav. 62, 7.
Gosling, L. M., Roberts, S. C., and Thornton, E. A., 2000a. Life history costs of olfactory
status signalling in mice. Behav Ecol Sociobiol. 48, 328-332.
22
Gosling, L. M., Roberts, S. C., Thornton, E. A., and Andrew, M. J., 2000b. Life history
costs of olfactory status signalling in mice. Behav Ecol Sociobiol. 48, 328-332.
Graham, J. M., and Desjardins, C., 1980. Classical conditioning: induction of luteinizing
hormone and testosterone secretion in anticipation of sexual activity. Science.
210, 1039-1041.
Grasselli, F., Gaiani, R., and Tamanini, C., 1992. Seasonal variation in the reproductive
hormones of male goats. Acta Endocrinol (Copenh). 126, 271-275.
Grether, G. F., Hudon, J., and Millie, D. F., 1999. Carotenoid limitation of sexual
coloration along an environmental gradient in guppies. Proc R Soc B. 266, 13171322.
Grossman, C. J., 1984. Regulation of the immune system by sex steroids. Endocr Rev. 5,
435-355.
Halliday, T. R., 1990. The evolution of courtship behavior in newts and salamanders.
Adv Stud Behav. 19, 137-169.
Hamada, T., Nakajima, M., Takeuchi, Y., and Mori, Y., 1996. Pheromone-induced
stimulation of hypothalamic gonadotropin-releasing hormone pulse generator in
ovariectomized, estrogen-primed goats. Neuroendocrinology. 64, 313-319.
Hamilton, W. D., and Zuk, M., 1982. Heritable true fitness and bright birds: a role for
parasites? Science. 218, 384-387.
Harding, C. F., and Follett, B. K., 1979. Hormone changes triggered by aggression in a
natural population of blackbirds. Science. 203, 918-920.
Hart, B. L., and Jones, T., 1975. Effects of castration on sexual behavior of tropical male
goats. Horm Behav. 6, 247-258.
Hau, M., 2007. Regulation of male traits by testosterone: implications for the evolution of
vertebrate life histories. Bioessays. 29, 133-44.
Hill, G. E., 1990. Female house finches prefer colourful males: sexual selection for a
condition-dependent trait. Anim Behav. 40, 563-572.
Hill, G. E., 1991. Plumage coloration is a sexually selected indicator of male quality.
Nature. 350, 337-339.
Hill, G. E., 1992. Proximate basis of variation in carotenoid pigmentation in male house
finches. Auk. 109, 1-12.
Hill, G. E., and Montgomerie, R., 1994. Plumage colour signals nutritional condition in
the house finch. Proc R Soc B. 258, 47-52.
Horne, T. J., and Ylonen, H., 1996. Female bank voles (Clethrionomys glareolus) prefer
dominant males; but what if there is no choice? Behav Ecol Sociobiol. 38, 401405.
Horne, T. J., and Ylönen, H., 1998. Heritabilities of dominance-related traits in male
bank voles (Clethrionomys glareolus). Evolution. 52, 894-899.
Houde, A. E., and Torio, A. J., 1992. Effect of parasitic infection on male color pattern
and female choice in guppies. Behav Ecol. 3, 346-351.
Illius, A. W., Haynes, N. B., and Lamming, G. E., 1976. Effects of ewe proximity on
peripheral plasma testosterone levels and behaviour in the ram. Reproduction. 48,
25-32.
Isbell, L. A., 1995. Seasonal and social correlates of changes in hair, skin, and scrotal
condition in vervet monkeys (Cercopithecus aethiops) of Amboseli National Park,
Kenya. Am J Primatol. 36, 61-70.
23
Iwata, E., Wakabayashi, Y., Kakuma, Y., Kikusui, T., Takeuchi, Y., and Mori, Y., 2000.
Testosterone-dependent primer pheromone production in the sebaceous gland of
male goat. Biol Reprod. 62, 806-810.
Iwata, E., Wakabayashi, Y., Matsuse, S., Kikusui, T., Takeuchi, Y., and Mori, Y., 2001.
Induction of primer pheromone production by dihydrogentestosterone in the male
goat. J Vet Med Sci. 63, 347-348.
Jainudeen, M. R., McKay, G. M., and Eisenberg, J. F., 1972. Observations on musth in
the domesticated Asiatic elephant (Elephas maximus). Mammalia. 36, 247-261.
Jiguet, F., and Bretagnolle, V., 2001. Courtship behaviour in a lekking species: individual
variations and settlement tactics in male little bustard. Behav Process. 55, 107118.
Johansson, B. G., and Jones, T. M., 2007. The role of chemical communication in mate
choice. Biol Rev Camb Philos Soc. 82, 265-289.
Jones, M. C., and Leighton Jr, A. T., 1987. Effect of presence or absence of the opposite
sex on egg production and semen quality of breeder turkeys. Poultry Sci. 66,
2056-2059.
Kaneko, N., Debski, E. A., Wilson, M. C., and Whitten, W. K., 1980. Puberty
acceleration in mice. II. Evidence that the vomeronasal organ is a receptor for the
primer pheromone in male mouse urine. Biol Reprod. 22, 873-878.
Karino, K., 1995. Male-male competition and female mate choice through courtship
display in the territorial damselfish Stegastes nigricans. Ethology. 100, 126-138.
Kavaliers, M., and Colwell, D. D., 1993. Aversive responses of female mice to the odors
of parasitized males: neuromodulatory mechanisms and implications for mate
choice. Ethology. 95, 202-212.
Kavaliers, M., and Colwell, D. D., 1995. Discrimination by female mice between the
odours of parasitized and non-parasitized males. Proc R Soc B. 261, 31-35.
Ketterson, E. D., Nolan Jr, V., Cawthorn, M. J., Parker, P. G., and Ziegenfus, C., 1996.
Phenotypic engineering: using hormones to explore the mechanistic and
functional bases of phenotypic variation in nature. Ibis. 138, 70-86.
Ketterson, E. D., Nolan, V., Jr., Wolf, L., Ziegenfus, C., Dufty, A. M., Jr., Ball, G. F.,
and Johnsen, T. S., 1991. Testosterone and avian life histories: the effect of
experimentally elevated testosterone on corticosterone and body mass in darkeyed juncos. Horm Behav. 25, 489-503.
Keverne, E. B., 1977. Pheromones and sexual behavior. Handbook of Sexology. 413—
425.
Kirkpatrick, M., 1996. Good genes and direct selection in the evolution of mating
preferences. Evolution. 50, 2125-2140.
Kleven, O., Jacobsen, F., Izadnegahdar, R., Robertson, R. J., and Lifjeld, J. T., 2006.
Male tail streamer length predicts fertilization success in the North American barn
swallow (Hirundo rustica erythrogaster). Behav Ecol Sociobiol. 59, 412-418.
Kodric-Brown, A., 1985. Female preference and sexual selection for male coloration in
the guppy (Poecilia reticulata). Behav Ecol Sociobiol. 17, 199-205.
Kodric-Brown, A., 1989. Dietary carotenoids and male mating success in the guppy: an
environmental component to female choice. Behav Ecol Sociobiol. 25, 393-401.
Koivula, M., and Korpimaki, 2001. Do scent marks increase predation risks of microtine
rodents? Oikos. 95, 275-281.
24
Kokko, H., 1997. Evolutionarily stable strategies of age-dependent sexual advertisement.
Behav Ecol Sociobiol. 41, 99-107.
Kokko, H., and LindstrÖm, J., 1996. Evolution of female preference for old mates. Proc
R Soc B. 263, 1533-1538.
Krebs, J. R., and Davies, N. B., 1978. Behavioural ecology: an evolutionary approach.
Sinauer Associates Inc., Massachusetts.
Kruuk, L. E. B., Slate, J., Pemberton, J. M., Brotherstone, S., Guinness, F., and CluttonBrock, T., 2002. Antler size in red deer: heritability and selection but no
evolution. Evolution. 56, 1683-1695.
Lawson, R. E., Putnam, R. J., and Fielding, A. H., 2000. Individual signatures in scent
gland secretions of Eurasian deer. J Zool. 251, 399-410.
Leonard, M. L., and Zanette, L., 1998. Female mate choice and male behaviour in
domestic fowl. Anim Behav. 56, 1099-1105.
Leonard, M. L., Zanette, L., Thompson, B. K., and Wayne Fairfull, R., 1993. Early
exposure to the opposite sex affects mating behaviour in White Leghorn chickens.
Appl Anim Behav Sci. 37, 57-67.
Leutenegger, W., and Kelly, J. T., 1977. Relationship of sexual dimorphism in canine
size and body size to social, behavioral, and ecological correlates in anthropoid
primates. Primates. 18, 117-136.
Lincoln, G. A., 1994. Teeth, horns and antlers: the weapons of sex. The differences
between the sexes. 131-158.
Lopez, P., Amo, L., and Martin, J., 2006. Reliable signaling by chemical cues of male
traits and health state in male lizards, Lacerta monticola. J Chem Ecol. 32, 473488.
MacIntosh Schellinck, H., Smyth, C., Brown, R., and Wilkinson, M., 1993. Odor-induced
sexual maturation and expression of c-fos in the olfactory system of juvenile
female mice. Dev Brain Res. 74, 138-141.
Maggioncalda, A. N., Sapolsky, R. M., and Czekala, N. M., 1999. Reproductive hormone
profiles in captive male orangutans: implications for understanding developmental
arrest. Am J Phys Anthropol. 109, 19-32.
Mainguy, J., and Côté, S. D., 2008. Age-and state-dependent reproductive effort in male
mountain goats, Oreamnos americanus. Behav Ecol Sociobiol. 62, 935-943.
Malo, A. F., Roldan, E. R. S., Garde, J., Soler, A. J., and Gomendio, M., 2005. Antlers
honestly advertise sperm production and quality. Proc R Soc B. 272, 149-157.
Manning, J. T., 1985. Choosy females and correlates of male age. J Theor Biol. 116, 349354.
Marler, C. A., and Moore, M. C., 1988. Evolutionary costs of aggression revealed by
testosterone manipulations in free-living male lizards. Behav Ecol Sociobiol. 23,
21-26.
Marler, C. A., and Moore, M. C., 1989. Time and energy costs of aggression in
testosterone-implanted free-living male mountain spiny lizards (Sceloporus
jarrovi). Physiol Zool. 62, 1334-1350.
Marsh, J. A., and Scanes, C. G., 1994. Neuroendocrine-immune interactions. Poultry Sci.
73, 1049-1253.
25
Martín-Vivaldi, M., Palomino, J. J., Soler, M., and Martínez, J. G., 1999. Song strophelength and reproductive success in a non-passerine bird, the Hoopoe Upupa
epops. Ibis. 141, 670-679.
Martins, M. I., de Souza, F. F., Oba, E., and Lopes, M. D., 2006. The effect of season on
serum testosterone concentrations in dogs. Theriogenology. 66, 1603-5.
Mateos, C., and Carranza, J., 1996. On the intersexual selection for spurs in the ringnecked pheasant. Behav Ecol. 7, 362.
McComb, K., 1987. Roaring by red deer stags advances the date of oestrus in hinds.
Nature. 330, 648-649.
McComb, K. E., 1991. Female choice for high roaring rates in red deer, Cervus elaphus.
Anim Behav. 41, 79-88.
McGinnis, M. Y., Christina Mirth, M., Zebrowski, A. F., and Dreifuss, R. M., 1989.
Critical exposure time for androgen activation of male sexual behavior in rats.
Physiol Behav. 46, 159-165.
McGlothlin, J. W., Jawor, J. M., Greives, T. J., Casto, J. M., Phillips, J. L., and Ketterson,
E. D., 2008. Hormones and honest signals: males with larger ornaments elevate
testosterone more when challenged. J Evol Biol. 21, 39-48.
McLintock, W. J., and Uetz, G. W., 1996. Female choice and pre-existing bias: visual
cues during courtship in two Schizocosawolf spiders (Araneae: Lycosidae). Anim
Behav. 52, 167-181.
Melrose, D. R., Reed, H. C., and Patterson, R. L., 1971. Androgen steroids associated
with boar odour as an aid to the detection of oestrus in pig artificial insemination.
Brit Vet J. 127, 497-502.
Milinski, M., and Bakker, T. C. M., 1990. Female sticklebacks use male coloration in
mate choice and hence avoid parasitized males. Nature. 344, 330-333.
Miller, K. V., Marchinton, R. L., Forand, K. J., and Johansen, K. L., 1987. Dominance,
testosterone levels, and scraping activity in a captive herd of white-tailed deer. J
Mammal. 68, 812-817.
Miquelle, D. G., 1991. Are moose mice? The function of scent urination in moose. Am
Nat. 138, 460-477.
Møller, A. P., 1988. Female choice selects for male sexual tail ornaments in the
monogamous swallow. Nature. 332, 640-642.
Mossman, C. A., and Drickamer, L. C., 1996. Odor preferences of female house mice
(Mus domesticus) in seminatural enclosures. J Comp Psychol. 110, 131-8.
Mougeot, F., and Bretagnolle, V., 2000. Predation as a cost of sexual communication in
nocturnal seabirds: an experimental approach using acoustic signals. Anim Behav.
60, 647-656.
Mougeot, F., Irvine, J. R., Seivwright, L., Redpath, S. M., and Piertney, S., 2004.
Testosterone, immunocompetence, and honest sexual signaling in male red
grouse. Behav Ecol. 15, 930-937.
Muduuli, D. S., Sanford, L. M., Palmer, W. M., and Howland, B. E., 1979. Secretory
patterns and circadian and seasonal changes in lutenizing hormone, follicle
stimulating hormone, prolactin and testosterone in the male pygmy goat. J Anim
Sci. 49, 543-553.
26
Murai, M., and Backwell, P. R. Y., 2006. A conspicuous courtship signal in the fiddler
crab Uca perplexa: female choice based on display structure. Behav Ecol
Sociobiol. 60, 736-741.
Nespor, A. A., Lukazewicz, M. J., Dooling, R. J., and Ball, G. F., 1996. Testosterone
induction of male-like vocalizations in female budgerigars (Melopsittacus
undulatus). Horm Behav. 30, 162-169.
Norris, K., 1993. Heritable variation in a plumage indicator of viability in male great tits
Parus major. Nature 362, 537-539.
Nunez, A. A., and Tan, D. T., 1984. Courtship ultrasonic vocalizations in male SwissWebster mice: Effects of hormones and sexual experience. Physiol Behav. 32,
717-721.
Olsen, K. H., Grahn, M., and Lohm, J., 2003. The influence of dominance and diet on
individual odours in MHC identical juvenile Arctic charr siblings. J Fish Biol. 63,
855-862.
Opuch, S., and Radwan, J., 2009. Condition dependence of sexual attractiveness in the
bank vole. Behav Ecol Sociobiol. 63, 339-344.
Penn, D., and Potts, W. K., 1998. Chemical signals and parasite-mediated sexual
selection. Trends Ecol Evol. 13, 391-396.
Penn, D., Schneider, G., White, K., Slev, P., and Potts, W., 1998. Influenza infection
neutralizes the attractiveness of male odour to female mice (Mus musculus).
Ethology. 104, 685-694.
Perkins, A., and Fitzgerald, J. A., 1994. The behavioral component of the ram effect: the
influence of ram sexual behavior on the induction of estrus in anovulatory ewes. J
Anim Sci. 72, 51-55.
Peters, A., 2000. Testosterone treatment is immunosuppressive in superb fairy-wrens, yet
free-living males with high testosterone are more immunocompetent. Proc R Soc
B. 267, 883.
Petrie, M., 1994. Improved growth and survival of offspring of peacocks with more
elaborate trains. Nature. 371, 598-599.
Pinxten, R., de Ridder, E., and Eens, M., 2003. Female presence affects male behavior
and testosterone levels in the European starling (Sturnus vulgaris). Horm Behav.
44, 103-109.
Price, E. O., Smith, V. M., and Katz, L. S., 1986. Stimulus conditions influencing selfenurination, genital grooming and flehmen in male goats. Appl Anim Behav Sci.
16, 371-381.
Pryke, S. R., Andersson, S., and Lawes, M. J., 2001. Sexual selection of multiple
handicaps in the red-collared widowbird: female choice of tail length but not
carotenoid display. Evolution. 55, 1452-1463.
Purvis, K., and Haynes, N. B., 1974. Short-term effects of copulation, human chorionic
gonadotrophin injection and non-tactile association with a female on testosterone
levels in the male rat. J Endocrinol. 60, 429-439.
Qvarnstroöm, A., 1997. Experimentally increased badge size increases male competition
and reduces male parental care in the collared flycatcher. Proc R Soc B. 264,
1225-1231.
Ralls, K., 1976. Mammals in which females are larger than males. Quart Rev Biol. 245276.
27
Ramenofsky, M., 1984. Agonistic behaviour and endogenous plasma hormones in male
Japanese quail. Anim Behav. 32, 698-708.
Rantala, M. J., Jokinen, I., Kortet, R., Vainikka, A., and Suhonen, J., 2002. Do
pheromones reveal male immunocompetence? Proc R Soc B. 269, 1681-1685.
Rasmussen, L. E., Riddle, H. S., and Krishnamurthy, V., 2002. Mellifluous matures to
malodorous in musth. Nature. 415, 975-6.
Rasmussen, L. E., and Schulte, B. A., 1998. Chemical signals in the reproduction of
Asian (Elephas maximus) and African (Loxodonta africana) elephants. Anim
Reprod Sci. 53, 19-34.
Reby, D., and McComb, K., 2003. Anatomical constraints generate honesty: acoustic
cues to age and weight in the roars of red deer stags. Anim Behav. 65, 519-530.
Reid, J. M., Arcese, P., Cassidy, A., Hiebert, S. M., Smith, J. N. M., Stoddard, P. K.,
Marr, A. B., and Keller, L. F., 2004. Song repertoire size predicts initial mating
success in male song sparrows, Melospiza melodia. Anim. Behav. 68, 1055–1063.
Rhen, T., and Crews, D., 2002. Variation in reproductive behaviour within a sex: neural
systems and endocrine activation. J Neuroendocrinol. 14, 517-531.
Rich, T. J., and Hurst, J. L., 1998. Scent marks as reliable signals of the competitive
ability of mates. Anim Behav. 56, 727-735.
Rich, T. J., and Hurst, J. L., 1999. The competing countermarks hypothesis: reliable
assessment of competitive ability by potential mates. Anim Behav. 58, 10271037.
Roberts, S. C., 2007. Scent marking. pp 255–266, In Wolff, J. and Sherman, P.W. (ed.).
Rodent Societies: an Ecological and Evolutionary Perspective. The University
Chicago Press.
Roberts, S. C., and Gosling, L. M., 2003. Genetic similarity and quality interact in mate
choice decisions by female mice. Nat Genet. 35, 103-106.
Ryan, M. J., and Brenowitz, E. A., 1985. The role of body size, phylogeny, and ambient
noise in the evolution of bird song. Am Nat. 87-100.
Ryser, J., 1989. Weight loss, reproductive output, and the cost of reproduction in the
common frog, Rana temporaria. Oecologia. 78, 264-268.
Sacchi, R., Galeotti, P., Fasola, M., and Ballasina, D., 2003. Vocalizations and courtship
intensity correlate with mounting success in marginated tortoises Testudo
marginata. Behav Ecol Sociobiol. 55, 95-102.
Saino, N., Primmer, C. R., Ellegren, H., and Møller, A. P., 1997. An experimental study
of paternity and tail ornamentation in the barn swallow (Hirundo rustica).
Evolution. 51, 562-570.
Schneider, R. A. Z., Huber, R., and Moore, P. A., 2001. Individual and status recognition
in the crayfish, Orconectes rusticus: the effects of urine release on fight dynamics.
Behaviour. 138, 137-153.
Schneider, R. A. Z., Schneider, R. W. S., and Moore, P. A., 1999. Recognition of
dominance status by chemoreception in the red swamp crayfish, Procambarus
clarkii. J Chem Ecol. 25, 781-794.
Searcy, W. A., and Yasukawa, K., 1996. Song and female choice. pp 454-473. In
Kroodsma, D. E. and Miller, E. H. (eds.). Ecology and evolution of acoustic
communication in birds. Cornell University Press.
28
Setchell, J. M., 2005. Do female mandrills prefer brightly colored males? Int J Primatol.
26, 715-735.
Setchell, J. M., and Dixson, A. F., 2001. Arrested development of secondary sexual
adornments in subordinate adult male mandrills (Mandrillus sphinx). Am J Phys
Anthropol. 115, 245-252.
Sheldon, B. C., Merila, J., Qvarnström, A., Gustafsson, L., and Ellegren, H., 1997.
Paternal genetic contribution to offspring condition predicted by size of male
secondary sexual character. Proc R Soc B. 264, 297-302.
Smith, H. G., and Montgomerie, R., 1991. Sexual selection and the tail ornaments of
North American barn swallows. Behav Ecol Sociobiol. 28, 195-201.
Snowder, G. D., Stellflug, J. N., and Van Vleck, L. D., 2002. Heritability and
repeatability of sexual performance scores of rams. J Anim Sci. 80, 1508.
Steklis, H. D., Brammer, G. L., Raleigh, M. J., and McGuire, M. T., 1985. Serum
testosterone, male dominance, and aggression in captive groups of vervet
monkeys (Cercopithecus aethiops sabaeus). Horm Behav. 19, 154-63.
Suttie, J. M., 1980. The effect of antler removal on dominance and fighting behaviour in
farmed red deer stags. J Zool. 190, 217-224.
Thomas, R. J., 2002. The costs of singing in nightingales. Anim Behav. 63, 959-966.
Thompson, C. W., Hillgarth, N., Leu, M., and McClure, H. E., 1997. High parasite load
in house finches (Carpodacus mexicanus) is correlated with reduced expression of
a sexually selected trait. Am Nat. 149, 270-294.
Thoren, S., Linerfors, P., and Kappeler, P. M., 2006. Phylogenetic analysis of
dimorphism in primates: evidence for stronger selection on canine size than on
body size. Am J Phys Anthropol. 130, 50-59.
Trivers, R. L. (1972). Parental investment and sexual selection. pp. 136-179 In B.
Campbell (Ed.), Sexual Selection and the descent of man 1871-1971. Aldine
Press, Chicago.
Vallet, E., Beme, I., and Kreutzer, M., 1998. Two-note syllables in canary songs elicit
high levels of sexual display. Anim Behav. 55, 291-297.
van der Meij, L., Buunk, A. P., van de Sande, J. P., and Salvador, A., 2008. The presence
of a women increases testosterone in aggressive dominant men. Horm Behav. 54,
640-644.
Vehrencamp, S. L., Bradbury, J. W., and Gibson, R. M., 1989. The energetic cost of
display in male sage grouse. Anim Behav. 38, 885-896.
Vinnedge, B., and Verrell, P., 1998. Variance in male mating success and female choice
for persuasive courtship displays. Anim Behav. 56, 443-448.
von Schantz, T., Grahn, M., and Goransson, G., 1994. Intersexual selection and
reproductive success in the pheasant Phasianus Colchicus. Am Nat. 144, 510-527.
Von Schantz, T., Wittzell, H., Göransson, G., and Grahn, M., 1997. Mate Choice, Male
Condition-Dependent Ornamentation and MHC in the Pheasant. Hereditas. 127,
133-140.
Wada, M., 1986. Circadian rhythms of testosterone-dependent behaviors, crowing and
locomotor activity, in male Japanese quail. J Comp Physiol A. 158, 17-25.
Waitt, C., Little, A. C., Wolfensohn, S., Honess, P., Brown, A. P., Buchanan-Smith, H.
M., and Perrett, D. I., 2003. Evidence from rhesus macaques suggests that male
29
coloration plays a role in female primate mate choice. Proc R Soc Lond B. 270,
S144-146.
Walkden-Brown, S. W., Martin, G. B., and Restall, B. J., 1999. Role of male-female
interaction in regulating reproduction in sheep and goats. J Reprod Fertil Suppl.
54, 243-57.
Walkden-Brown, S. W., Restall, B. J., and Henniawati, 1993b. The male effect in the
Australian cashmere goat. Role of olfactory cues from the male. Anim
Reprodtion Science 32, 55-67.
Walkden-Brown, S. W., Restall, B. J., Norton, B. W., and Scaramuzzi, R. J., 1994a. The
"female effect" in Australian cashmere goats: effect of season and quality of diet
on the LH and testosterone response of bucks to oestrous does. J Reprod Fertil.
100, 521-31.
Walkden-Brown, S. W., Restall, B. J., Norton, B. W., Scaramuzzi, R. J., and Martin, G.
B., 1994b. Effect of nutrition on seasonal patterns of LH, FSH and testosterone
concentration, testicular mass, sebaceous gland volume and odour in Australian
Cashmere goats. J Reprod Fertil. 102, 351-60.
Walther, F. R., 1984. Communication and expression in hoofed mammals. Indiana
University Press.
Ward, S., Speakman, J. R., and Slater, P. J. B., 2003. The energy cost of song in the
canary, Serinus canaria. Anim Behav. 66, 893-902.
Welch, A. M., Semlitsch, R. D., and Gerhardt, H. C., 1998. Call duraton as an indicator
of genetic quality in male gray tree frogs. Science. 280, 1928-1929.
West, P. M., and Packer, C., 2002. Sexual selection, temperature, and the lion's mane.
Science. 297, 1339-1343.
Whittle, C., Bowyer, R. T., Clausen, T. P., and Duffy, L. K., 2000. Putative pheromones
in urine of rutting male moose (Alces alces): evolution of honest advertisement? J
Chem Ecol. 26, 2747-2762.
Wickings, E. J., 1993. Hypervariable single and multi-locus DNA polymorphisms for
genetic typing of non-human primates. Primates. 34, 323-331.
Widowski, T. M., Lo Fo Wong, D. M., and Duncan, I. J., 1998. Rearing with males
accelerates onset of sexual maturity in female domestic fowl. Poultry Sci. 77, 150.
Wiley, C. J., and Goldizen, A. W., 2003. Testosterone is correlated with courtship but not
aggression in the tropical buff-banded rail, Gallirallus philippensis. Horm Behav.
43, 554-60.
Wilson, J. D., George, F. W., and Griffin, J. E., 1981. The hormonal control of sexual
development. Science. 211, 1278-84.
Wingfield, J. C., 1984. Androgens and mating systems: testosterone-induced polygyny in
normally monogamous birds. Auk. 101, 665-671.
Wingfield, J. C., 1985. Short-term changes in plasma levels of hormones during
establishment and defense of a breeding territory in male song sparrows,
Melospiza melodia. Horm Behav. 19, 174-187.
Wingfield, J. C., Ball, G. F., Dufty Jr, A. M., Hegner, R. E., and Ramenofsky, M., 1987.
Testosterone and aggression in birds. Am Sci. 75, 602-608.
Winquist, T., and Lemon, R. E., 1994. Sexual selection and exaggerated male tail length
in birds. Am Nat. 143, 95-116.
30
Wolff, J. O., 1998. Breeding strategies, mate choice, and reproductive success in
American bison. Oikos. 83, 529-544.
Wyatt, T. D., 2003. Pheromones and animal behaviour. Cambridge University Press
Cambridge, UK:.
Yahr, P., Newman, A., and Stephen, D. R., 1979. Sexual behavior and scent marking in
male gerbils: Comparison of changes after castration and testosterone
replacement. Horm Behav. 13, 175-184.
Yahr, P., and Thiessen, D. D., 1972. Steroid regulation of territorial scent marking in the
Mongolian gerbil (Meriones unguiculatus). Horm Behav. 3, 359-368.
Yang, J., Long, D. W., Inpanbutr, N., and Bacon, W. L., 1998. Effects of photoperiod and
age on secretory patterns of luteinizing hormone and testosterone and semen
production in male domestic turkeys. Biol Reprod. 59, 1171-1179.
Young, W. C., Goy, R. W., and Phoenix, C. H., 1964. Hormones and Sexual Behavior.
Science. 143, 212-218.
Zeuner, F. E., 1963. A history of domesticated animals. Hutchinson & Co.
Zula, S. M., Potts, W. K., and Penn, D. J., 2004. Scent-marking displays provide honest
signals of health and infection. Behav Ecol. 15, 338-344.
31
CHAPTER II
ESTROUS FEMALE GOATS USE TESTOSTERONE-DEPENDENT
CUES TO ASSESS MATES
Published in:
Hormones and Behavior. In Press. doi:10.1016/j.yhbeh.2010.10.014
32
ABSTRACT
In a promiscuous species like the domestic goat (Capra hircus), in which
maternal investment is greater than paternal investment, a female may mate selectively
with a more-fit male to improve her reproductive fitness. Testosterone (T) controls a
large suite of male-typical behaviors and morphological characteristics. High T
concentrations may be energetically costly or even detrimental to survival; thus,
preventing lower quality males from falsely advertising their fitness. Three preference
studies were conducted to examine if females use T-dependent cues to assess potential
mates. For Experiment 1, females were given a choice between a pair of morphologically
similar males, bucks (intact males) and stags (post-pubertally castrated males), during the
breeding and non-breeding seasons. In both seasons, females preferred the bucks
compared to stags. In Experiment 2, females were given a choice between bucks, stags
and wethers (pre-pubertally castrated males) during the non-breeding season. For some
comparisons, castrated males received 25mg testosterone propionate (TP) or were
untreated. Females preferred TP-treated males compared to untreated males and showed
no preference when given a choice between either two TP-treated or two untreated males.
In Experiment 3, females were given a choice between a pair of bucks and a pair of stags
treated with 25mg TP during monthly tests in the breeding season. At each monthly test,
females preferred the males with higher T concentrations near the time of the behavior
test. These studies suggest that females use T-dependent cues to assess potential mates,
and T concentrations may indicate a male’s overall fitness.
Key words: Female mate choice, testosterone, reproductive behavior, fitness, goat
33
INTRODUCTION
Female mate choice is the ability of a female to distinguish among, and mate
selectively with, specific phenotypes (Krebs and Davies, 1978). Sexual selection theories
suggest that for promiscuous species in which males and females breed with several
partners and there is no paternal care, females often breed with higher quality mates.
Males, on the other hand, will attempt to breed with a large number of partners (Trivers,
1972). The ability of the female to distinguish among high and low quality males is of
critical importance and is a major determinant of her reproductive fitness. Extravagant
secondary sexual characteristics such as bright coloration, intricate songs, ornate visual
signals and chemical cues have all received considerable attention in the study of sexual
selection, as females often choose to mate with individuals displaying such characteristics
(Andersson, 1982; Gentner and Hulse, 2000; Gosling and Roberts, 2001; Waitt, et al.,
2003). Although extravagant characteristics may predispose males to predation, these
cues may serve as an honest indicator of a male’s fitness and increase his access to
potential mates (Darwin, 1871). Females that choose individuals displaying extravagant
characteristics will increase the likelihood that their male offspring will also be preferred,
thus, increasing the female’s reproductive fitness.
For many species, testosterone (T) regulates the expression of a large suite of
male secondary sexual characteristics (reviewed in: Hau, 2007; Rhen and Crews, 2002).
High T concentrations may impose a cost to the male as they have been shown to
negatively affect a male’s health by causing immune suppression (Grossman, 1984;
Marsh and Scanes, 1994; Mougeot, et al., 2004; Peters, 2000). Duckworth et al. (2001)
and Folstad and Karter (1992) argue that T-dependent cues are plastic and dependent
34
upon health condition, specifically parasite load. Accordingly, males with higher parasite
loads display a lower expression of secondary sexual characteristics than males with
lower parasite loads as demonstrated by Thompson’s et al. (1997) findings that males
with higher parasite load during molt had reduced development of bright male plumage.
High T concentrations have also been shown to be energetically costly for a male to
maintain, causing increased metabolic rate (Buchanan, et al., 2001) and an increase in the
loss of fat reserves (Ketterson, et al., 1991; Wingfield, 1984). Further, expressing maletypical reproductive behaviors such as territory marking and defense, mate guarding and
courtship are costly as males cannot simultaneously forage or hunt for food (Gaunt, et al.,
1996; Marler and Moore, 1989), likely leading to decreased body weights. Males with
limited access to food or in poor health would not be able to display and/or maintain a
high expression of secondary sexual characteristics (Zahavi, 1975). In effect, T
production and resulting T-dependent characteristics may be an honest indicator of a
male’s potential fitness. Altogether, males that have higher circulating T concentrations
are more likely to be preferred by females than males with lower T concentrations.
In the majority of seasonally-breeding species, males show a circannual increase
and decrease in circulating T concentrations. Testosterone concentrations increase and
reach maximal concentrations early in the breeding season and decrease thereafter,
becoming minimal in the non-breeding season (Busso, et al., 2005; Delgadillo, et al.,
2004). During the breeding season, high serum T concentrations permit the expression of
secondary sexual characteristics. In the non-breeding season, there is a decrease in size
and activity of the testes (Goritz, et al., 2006; Minter and DeLiberto, 2008; Riters, et al.,
2000) and an associated decrease in the production of reproductive hormones,
35
specifically T. Further, there is a deficit in male-typical reproductive behaviors and
secondary sexual characteristics. Castration prior to puberty, often results in males
displaying a deficit of T-dependent characteristics. Males castrated post-pubertally show
a decrease in reproductive behaviors, sometimes taking upwards of 12 months before
there is a complete loss in reproductive behavior (Costantini, et al., 2007; D'Occhio and
Brooks, 1980; Davidson, 1966; Hart and Jones, 1975). Testosterone replacement can
restore these characteristics similar to the level of an intact male during the breeding
season (Beach, 1949; D'Occhio and Brooks, 1980; Foote, et al., 1977; McGinnis, et al.,
1989).
In addition, females may also use male morphology, as a means of distinguishing
between sexually mature and immature males. Morphological characteristics such as
darkening of the mane in lions (West and Packer, 2002), the number of feathers in the
peacock’s train (Manning, 1989), and body size of elephant seals (Haley, et al., 1994), are
all examples of age-dependent morphological characteristics that females may use to
distinguish between sexually mature and immature males. In a variety of species,
including beetles (Conner, 1989), goats (Cote and Hunte, 1993), black-billed magpies
(Komers and Dhindsa, 1989), African elephants (Poole, 1989), and crickets (Zuk, 1988),
females have shown a preference for older males as mates. One justification for this
preference is that age-dependent characteristics, rather than T concentrations may be an
honest indicator of genetic quality, and good genes may account for the increased
survivability of older males. In mating with older males, females stand to benefit from
these good genes by passing them on to their offspring.
36
The goat is an excellent model for the study of female mate choice. In the wild,
goats are promiscuous and offspring care is exclusively maternal. Thus, the goat (Capra
hircus) meets the criteria for a species that should display mate choice. As a domestic
species, the goat can be managed and manipulated for experimentation, allowing for a
more thorough understanding of mate choice in a large mammalian species. Male goats
undergo seasonal behavioral and physiological changes that may be T-dependent. Use of
males castrated pre-pubertally (morphologically immature) or post-pubertally
(morphologically mature), provides the ability to separate morphological cues from other
T-dependent cues such as behavior or chemical signaling to gain a better understanding
of female preference. It is predicted that females are using a T-dependent cue(s) to
distinguish among males. The objectives of this study were to examine if morphological
and/or other T-dependent cues are used by females to assess potential mates.
37
MATERIALS AND METHODS
Animals
All animals were Alpine goats between the ages of 1.5-9 years which received a
diet consisting of grass hay and grain, and had ad libitum access to water and mineral salt
blocks. Diet and husbandry was in compliance with the Consortium Guide for the Care
and Use of Agricultural Animals in Agricultural Research and Education (FASS, 2010).
Research was conducted as approved by the Rutgers University Animal Care and
Facilities Committee. Male and female goats were housed on the NJ Agricultural
Experiment Station Research Farm in New Brunswick, NJ (40° 29' 10" N / 74° 27' 8" W)
in barns with free access to outdoor exercise areas. The breeding season for the Alpine
goat begins in mid-August and terminates near the end of January in the northern
hemisphere. Focal goats were estrous-synchronized females. Goal males used in the
preference tests were in various reproductive states. Bucks are gonadally intact males
with typical male morphological characteristics including a muscular neck and thick
beard. Stags are males castrated post-pubertally and they have morphological
characteristics similar to those of a buck. Wethers are males castrated pre-pubertally and
they have morphological characteristics similar to those of females (Fig. 1).
Estrus Synchronization and Detection
Focal goats were estrus-synchronized females drawn from a herd of 24. The herd
was divided into two groups which were estrus-synchronized on alternating weeks. Estrus
synchronization was accomplished using a sequential treatment with prostaglandin
(PGF 2α ). During the breeding season each female received two injections of 10 mg
PGF 2α (dinoprost tromethamine, i.m.) at 13 days prior and 51 hours prior to the behavior
38
test as modified from Ott et al. (1980). For experiments conducted as females entered the
non-breeding season, estrus was either synchronized using the protocol above or induced
by providing exogenous progestins and estradiol from the protocol developed by Billings
and Katz (1997, 1999).
Standing estrus was detected prior to each behavior test. A non-experimental
buck was brought into the females’ home pen and allowed to mount females but not
allowed to intromit. If the female stood to be mounted, she was considered to be in estrus.
If the female rejected the male, she was considered non-estrous. All females, regardless
of estrous state, were tested in the behavior experiment; however, only data from estrous
females are reported. The number of estrous females used in each preference test is
indicated in Table 1.
Testosterone Propionate Treatment
Castrated males received 25 mg testosterone propionate (TP) s.c., 3x/week
beginning one month prior to the behavior test (TP-treated males are designated as
Wether TP or Stag TP). Previous studies by our laboratory have shown that 25 mg is
sufficient to activate male reproductive behaviors in wethers (unpublished data).
Injections continued until all behavior tests were completed (Exp. 2) or until the last 48hr blood sampling (Exp. 3).
Blood Sampling and Radioimmunoassay (RIA)
Blood samples were collected for Experiment 3 only. One week following each
monthly preference test, blood samples were taken from the males used in the preference
test via jugular venipuncture over a 48-hr period at the following time points relative to
39
the injection of TP: 0, 0.25, 0.5, 1, 2, 6, 12, 24, and 48 h. Serum was stored at -20 °C
until assayed.
Serum T concentrations were determined by commercial RIA kit (Beckman
Coulter DSL-4000, Webster, TX), validated in our laboratory for goat serum. The
minimum detection limit of the assay was 0.05 ng/ml, and the inter-assay coefficient of
variation was 11%.
Partner Preference Testing
Females were acclimated to the test apparatus (Fig. 2) for two weeks prior to the
behavior test. Trials commenced once all females showed no signs of stress (e.g.,
vocalizing, jumping) while in the test apparatus.
Prior to the start of each behavior test, goal males were placed within the holding
pens at both ends of the test apparatus and remained there for the duration of the trial. For
Experiments 1 and 3, each holding pen contained two males. For Experiment 2, one of
the males jumped out of the holding pen resulting in only one male being placed in each
holding pen for all comparisons made. Goal males used for each choice test varied and
some received TP treatment or were untreated as indicated in Table 1. For each
experiment, males used were randomly chosen from a larger pool of males: bucks (n = 6),
stags (n = 2), wethers (n = 6). Accordingly, different males were used for each choice test
within Experiments 1 and 2. For Experiment 3, the same two stags and two bucks were
used for all choice tests.
To account for any side biases, a switchback design was used. Accordingly,
female subjects were placed in the test apparatus for two trials. During each trial, the
female was led to the center of the neutral zone and released. She was allowed to travel
40
the test apparatus for 5 min. Use of a 5-min trial period was determined after observation
of estrous females within the test apparatus. Preference trials lasting longer than 5 min,
resulted in females becoming agitated. Further, for all experiments conducted, females
visited both sides of the apparatus within the allotted time. Total time spent in the
incentive zone near each male was recorded for each trial. For the switch back, males
were removed from the holding pen on one end of the test apparatus and placed in the
holding pen on the opposite end of the test apparatus. Females were then re-tested using
the same protocol as above.
Statistical Analysis
For each of the two trials, the female’s preference for a particular male (e.g., buck
versus untreated stag) was computed by calculating a score as follows:
For each female, the two preference scores for a particular male were averaged.
Preference scores were determined to be different from chance (50%) using a binomial
test. Variation in preference scores is reported as standard error of the proportion (±
SEP). Differences in serum T concentrations between bucks and TP-treated stags were
compared using a t test for independent samples. Results were deemed significant at
P<0.05 (NCSS Statistical Software, 2001, Kaysville, UT).
41
RESULTS
Experiment 1
Estrous females were given preference tests between bucks and untreated stags in
the breeding and non-breeding season. Preference scores for the choice tests completed
during the breeding and non-breeding season are presented in Figure 3. Estrous female
goats demonstrated a preference for bucks in both the breeding and non-breeding seasons
(P<.001).
Experiment 2
Females were given preference tests with the following choices: Buck vs Stag TP,
Stag TP vs Wether TP, Untreated Stag vs Wether TP and Untreated Wether vs Wether
TP. Preference scores for choice tests performed in the non-breeding season are presented
in Figure 4. Estrous female goats demonstrated a preference for males treated with TP
(P<.001). Estrous females demonstrated no preference when goal males were either both
treated with TP or both untreated.
Experiment 3
Estrous females were tested in monthly preference test comparing Buck vs. Stag
TP during the breeding season. Preference scores for the choice tests performed
throughout the breeding season are presented in Figure 5. Estrous female goats
demonstrated a preference for bucks in September and October (P<.05), then no
preference in November. Later in the breeding season, in December and January, estrous
female goats preferred the TP-treated stags (P <.05).
Serum T concentrations for the bucks and TP-treated stags throughout the
breeding season are presented in Figure 5. Serum T concentrations were significantly
42
higher for bucks during September and October compared to TP-treated stags (P <.05). In
November there was no difference but late in the breeding season (December and
January) T concentrations were greater in the TP-treated stags (P <.05).
43
DISCUSSION
Estrous female goats displayed a clear preference for males with higher serum T
concentrations regardless of their morphology. Meyer, et al. (1988) examined androgen
receptor concentrations in the sexually dimorphic neck and fore body region of cattle and
found that these areas are highly androgen sensitive, likely due to an increased number of
androgen receptors. Prepubertal castration of male calves led to a decrease in fore body
and neck muscles in comparison to intact males. For this study, stags were castrated
postpubertally, allowing for the development of their fore body and neck areas. If female
goats were choosing males solely on morphological cues, it would have been expected
that they would show no preference for either bucks or untreated stags. However, females
showed preference for bucks. Once an animal has stopped growing, morphological
changes resulting from increasing or decreasing T concentrations may be less plastic and
morphological changes are minimal. Ball (1940) found that after injecting female rats
with TP (0.1-0.2 mg) daily for 3 weeks, females showed masculine sexual behavior
similar to that of intact males, but no morphological changes occurred. Generally, pre- or
post-pubertal castration results in a reduced display or complete deprivation of
reproductive behaviors (reviewed in: Perkins and Roselli, 2007; Katz, 2007). The
female’s ability to distinguish between and show preference for bucks is likely due to the
T-dependent characteristics or cues displayed by the bucks in comparison to those cues
displayed by the stags.
During the non-breeding season, females showed preference for the TP-treated
males regardless of male morphology. A variety of ruminants display seasonal
fluctuations in T concentrations and reproductive characteristics, including goats
44
(Muduuli et al., 1979), sheep (Sanford et al., 1977), and Père David’s deer (Li et al.,
2001). Both T concentrations and the expression of reproductive behaviors, as well as the
emanation of chemical cues, peak at the onset of the breeding season and return to
minimal levels during the non-breeding season. Thus, T concentrations for the bucks in
the current study were assumed to be lower during the non-breeding season than during
the breeding season (Muduuli et al., 1979). Further, T concentrations for the bucks were
assumed to be lower during the non-breeding season than those of the TP-treated wethers
as reflected by results shown in Figure 5 for December and January as bucks were
entering the transition from breeding to non-breeding season. Females did not
discriminate when comparing TP-treated wethers to TP-treated stags nor did they
discriminate when comparing untreated wethers to untreated stags. Although stags and
wethers are morphologically different, the TP-treated males received the same frequency
and dose of TP possibly resulting in similar serum T concentrations and expression of Tdependent reproductive behaviors and chemical cues. Clegg et al. (1969) treated rams
castrated pre- and postpubertally with 50 mg TP, resulting in both groups displaying
similar frequencies of copulatory behavior. Although only number of mounts and
ejaculations were measured, males likely displayed other T-dependent reproductive
behaviors in order to mount receptive ewes. Since number of mounts between the preand post-pubertally castrated males was similar, other T-dependent behaviors may have
also been similar. In Experiment 2 of the current study, the females’ lack of preference
for one TP-treated male over the other may be a result of both males displaying Tdependent cues of a high quality male making preference for one unnecessary. Since
females did not show preference for either the stags or wethers when both were either
45
treated or un-treated, it suggests that morphological cues were not used by the female
when assessing males. Females preferred TP-treated wethers over the untreated stags or
wethers, further affirming that T concentrations, not male morphology, influence mate
preference in goats. Females showed preference for TP-treated males, rather than a
specific male phenotype. Taken together, these data confirm that females use Tdependent cues to distinguish among males. It is possible that age-dependent
morphological characteristics may be less variable than other cues and, thus, may not be
an honest indicator of fitness.
During the breeding season, male goats display reproductive behaviors, including
scent marking (chemical) and courtship cues that may serve as T-dependent cues for
females. Reproductive behaviors were not measured in this study; however, evidence
suggests that these cues are T-dependent and may provide a mechanism that females use
to distinguish among high and low quality males. The “male effect” is a well-studied
phenomenon, whereby placing intact or T-replaced males or their hair near anestrous
females prior to the onset of the breeding season hastens the onset of the breeding season
and synchronizes estrous cycles (Delgadillo et al., 2006, 2009; Gelez and Fabre-Nys,
2004, 2006; Walkden-Brown et al., 1993). The same chemical cues provided by the male
to induce this phenomenon may also be used by the female for mate choice. Iwata et al.
(2000) found that male goat sebaceous gland size and pheromone activity, which may be
responsible for the “male effect”, are T-dependent. Olfactory cues are also T-dependent
for elephants (Jainudeen et al., 1972; Poole et al., 1984; Rasmussen et al., 2002; Schulte
and Rasmussen, 1999), deer (Atkeson and Marchinton, 1982; Lincoln et al., 1972), and a
variety of rodents (Johnston, 1981; Wolff, 2004; Yahr et al., 1979). Studies have found
46
that females show preference for odors from males with higher T concentrations (Dunbar,
1977; Ferkin et al., 1994; Johnston, 1979; Signoret, 1970; Taylor et al., 1982). Courtship
may be another cue displayed by the male that is also T-dependent. Castrated sheep
treated with androgens show an increased frequency in courtship behaviors compared to
that displayed prior to androgen treatment (Banks, 1964; Marit et al., 1979; Parrott,
1978). Rivas-Munoz et al. (2007) found that 95% of previously anestrous females
ovulated in response to exposure to sexually active males (i.e., displaying courtship and
chemical cues) as opposed to only 15% exposed to sexually inactive males. Rate (Jiguet
and Bretagnolle, 2001; Knapp and Kovach, 1991; Patricelli et al., 2002), frequency
(Karino, 1995; Vinnedge and Verrell, 1998), and duration (Seymour and Sozou, 2009) of
courtship display are characteristics that have been well studied, with higher performing
males being preferred among females.
In the majority of seasonal breeders, timing of birth is crucial for offspring
survival (Clutton-Brock et al., 1987; Côté and Festa-Bianchet, 2001; Fairbanks, 1993;
Green and Rothstein, 2009) because offspring born early in temperate environments have
longer access to high-quality food than those born later in the season. Thus, if possible,
females should breed early in the breeding season to further aid in improving their
reproductive success. To maximize fitness, females need to be able to distinguish
between high and low quality males throughout the breeding season, as they may not
become pregnant after their first estrous cycle. In Experiment 3, we tested how accurately
females could distinguish among males that have different concentrations of T during the
breeding season. The design of this experiment also examined if females were reanalyzing a male’s fitness upon every encounter throughout the breeding season. TP-
47
treated stags used in the experiment maintained relatively consistent T concentrations
throughout the breeding season. Testosterone concentrations in the bucks naturally
fluctuated, with maximal T concentrations occurring at the onset of the breeding season
and then decreasing as the breeding season progressed. Testosterone-dependent
reproductive cues should parallel T concentrations; thus, cues should remain relatively
constant for the TP-treated stags and they should fluctuate for the buck. Accordingly, it
was expected that females would initially show preference for bucks, but as the breeding
season progressed and T concentrations fell naturally, preference would shift to the TPtreated stags. As predicted, as T concentrations in the bucks changed, females’ preference
shifted, always preferring the males with higher T concentrations. At the beginning of the
breeding season (September and October), the difference between the T concentrations of
the buck and TP-treated stags was great. In contrast, the difference in T concentrations
between the bucks and TP-treated stags was much less in December, yet females were
able to distinguish between and showed a preference for the males with higher T
concentrations. Thus, a female’s ability to make such fine distinctions suggests that Tdependent cues displayed by the males are important contributors to the fitness of
females.
In summary, female goats prefer males with higher serum T concentrations over
those with lower T concentrations. The T-dependent cues (e.g., scent marking or
courtship behavior) that females are using to differentiate between males are not yet
known and warrant further investigation. Serum T concentrations may be an honest
indicator of fitness. Males with higher serum T concentrations may be healthier, allowing
48
for high T concentrations to be maintained. This being the case, females that use this
honest cue to distinguish among males should gain fitness benefits.
ACKNOWLEDGEMENTS
We would like to acknowledge Susan E. Becker for her excellent technical
assistance. We would also like to thank our Animal Science undergraduate students who
helped conduct this research. This work was supported by the NJ Agricultural
Experiment Station, project 06144.
49
Table 1
Choice
1
2
3
Reproductive
Season
Buck vs. Untreated Stag
Buck vs. Untreated Stag
Buck vs. Stag TP
Stag TP vs. Wether TP
Untreated Stag vs. Wether TP
Untreated Wether vs. Wether TP
Untreated Stag vs. Untreated
Wether
Breeding
Non-breeding
Non-breeding
Non-breeding
Non-breeding
Non-breeding
Non-breeding
Buck vs. Stag TP - repeated
monthly
Breeding
Table 1. Female Preference Tests by Experiment
# of Estrous
Females
Tested
n=5
n = 10
n = 13
n = 10
n = 12
n=9
n = 12
Sep: n = 9
Oct: n = 12
Nov: n = 8
Dec: n = 8
Jan: n = 10
50
Figure 1
Figure 1. Goat phenotypes: Note similarities between buck and stag morphology as
well as female and wether morphology.
51
Figure 2
Figure 2. Test apparatus for female mate choice paradigm: The apparatus was
divided in the middle by a 2.4 m neutral zone. The neutral zone was defined by two 2.4 m
wide pieces of shade cloth that reached floor to ceiling and were against opposite walls
such that the openings to the incentive zones were staggered. Each incentive zone
contained a 1.5 m x 3 m holding pen.
52
Figure 3
Figure 3. Estrous females prefer bucks in the breeding and non-breeding season:
Mean (± SEP) preference score during 5-min partner preference tests for Buck vs. Stag
with respect to reproductive season. Number of estrous females varied for each
preference test and is indicated. Stags were untreated. * Significant difference (P<0.001).
53
Figure 4
Figure 4. Estrous females prefer TP-treated males regardless of male morphology:
Mean (± SEP) preference score during 5-min partner preference tests during the nonbreeding season. Number of estrous females varied for each preference test and is
indicated. Stags and wethers were either receiving TP-treatment as indicated by TP or
were untreated. * Significant difference (P<0.001).
54
Figure 5
Figure 5. Estrous females prefer males with higher T concentrations at the time of
the behavior test: (A) mean (± SEP) preference score during 5-min partner preference
tests. Number of estrous females varied for each preference test: September (n= 9),
October (n= 12), November (n=8), December (n=8), January (n=10). (B) Mean (± SEM)
serum T concentrations for a pair of bucks and a pair of TP-treated stags during the
breeding season. Testosterone concentrations are represented as area under the curve for
monthly 48-hr collections. Stags were receiving TP-treatment throughout the study. *
Significant difference (P<0.05).
55
REFERENCES
Andersson, M., 1982. Female choice selects for extreme tail length in a widowbird.
Nature. 299, 818-820.
Atkeson, T. D., and Marchinton, R. L., 1982. Forehead glands in white-tailed deer. J
Mammal. 63, 613-617.
Ball, J., 1940. The effect of testosterone on the sex behavior of female rats. J Comp
Psychol. 29, 151-165.
Banks, E. M., 1964. Some aspects of sexual behavior in domestic sheep, Ovis aries.
Behaviour. 23, 249-279.
Beach, F. A., 1949. Sexual behavior as a function of androgen concentration. Science.
109, 444.
Billings, H. J., and Katz, L. S., 1997. Progesterone facilitation and inhibition of estradiolinduced sexual behavior in the female goat. Horm Behav. 31, 47-53.
Billings, H. J., and Katz, L. S., 1999. Facilitation of sexual behavior in French-Alpine
goats treated with intravaginal progesterone-releasing devices and estradiol during
the breeding and nonbreeding seasons. J Anim Sci. 77, 2073-2078.
Buchanan, K. L., Evans, M. R., Goldsmith, A. R., Byrant, D. M., and Rowe, L. V., 2001.
Testosterone influences basal metabolic rate in male house sparrows: a new cost
of dominance signaling? Proc R Soc Lond B. 268, 1337-1344.
Busso, J. M., Ponzio, M. F., de Cuneo, M. F., and Ruiz, R. D., 2005. Year-round
testicular volume and semen quality evaluations in captive Chinchilla lanigera.
Anim Reprod Sci. 90, 127-134.
Clegg, M. T., Beamer, W., and Bermant, G., 1969. Copulatory behaviour of the ram, Ovis
aries. III: Effects of pre-and postpubertal castration and androgen replacement
therapy. Anim Behav. 17, 712-717.
Clutton-Brock, T. H., Major, M., Albon, S. D., and Guinness, F. E., 1987. Early
development and population dynamics in red deer. I. Density-dependent effects
on juvenile survival. J Anim Ecol. 56, 53-67.
Conner, J., 1989. Older males have higher insemination success in a beetle. Anim Behav.
38, 503-509.
Costantini, R. M., Park, J. H., Beery, A. K., Paul, M. J., Ko, J. J., and Zucker, I., 2007.
Post-castration retention of reproductive behavior and olfactory preferences in
male Siberian hamsters: role of prior experience. Horm Behav. 51, 149-155.
Cote, I. M., and Hunte, W., 1993. Female red lip blennies prefer older males. Anim
Behav. 46, 203-205.
Côté, S. D., and Festa-Bianchet, M., 2001. Birthdate, mass and survival in mountain goat
kids: effects of maternal characteristics and forage quality. Oecologia. 127, 230238.
D'Occhio, M. J., and Brooks, D. E., 1980. Effects of androgenic and oestrogenic
hormones on mating behaviour in rams castrated before or after puberty. J
Endocrin. 86, 403-411.
Darwin, C., 1871. The Descent of Man, and Selection in Relation to Sex. Murray,
London.
Davidson, J. M., 1966. Characteristics of sex behaviour in male rats following castration.
Anim Behav. 14, 266-272.
56
Delgadillo, J. A., Cortez, M. E., Duarte, G., Chemineau, P., and Malpaux, B., 2004.
Evidence that the photoperiod controls the annual changes in testosterone
secretion, testicular and body weight in subtropical male goats. Reprod Nutr Dev.
44, 183-193.
Delgadillo, J. A., Flores, J. A., Veliz, F. G., Duarte, G., Vielma, J.,Hernandez, H., and
Fernandez, I. G., 2006. Importance of the signals provided by the buck for the
success of the male effect in goats. Reprod Nutr Dev. 46, 391-400.
Delgadillo, J. A., Gelez, H., Ungerfeld, R., Hawken, P. A., and Martin, G. B., 2009. The
'male effect' in sheep and goats--revisiting the dogmas. Behav Brain Res. 200,
304-314.
Duckworth, R. A., Mendonca, M. T., and Hill, G. E., 2001. A condition dependent link
between testosterone and disease resistance in the house finch. Proc R Soc Lond
B. 268, 2467-2472.
Dunbar, I. F., 1977. Olfactory preferences in dogs: the response of male and female
beagles to conspecific odors. Behav Biol. 20, 471-481.
Fairbanks, W. S., 1993. Birthdate, birthweight, and survival in pronghorn fawns. J
Mammal. 74, 129-135.
FASS, 2010. Guide for the care and use of agricultural animals in research and
teaching, 3rd ed. Fed. Anim. Sci. Soc., Champagne, IL.
Ferkin, M. H.,Sorokin, E. S.,Renfroe, M. W., andJohnston, R. E., 1994. Attractiveness of
male odors to females varies directly with plasma testosterone concentration in
meadow voles. Physiol Behav. 55, 347-353.
Folstad, I., and Karter, A. J., 1992. Parasites, bright males, and the immunocompetence
handicap. Am Nat. 139, 603-622.
Foote, R. H., Draddy, P. J., Breite, M., and Oltenacu, E. A., 1977. Action of androgen
and estrone implants on sexual behavior and reproductive organs of castrated
male rabbits. Horm Behav. 9, 57-68.
Gaunt, A. S.,Bucher, T. L., Gaunt, S. L. L., and Baptista, L. F., 1996. Is singing costly?
Auk. 113, 718-721.
Gelez, H., and Fabre-Nys, C., 2004. The "male effect" in sheep and goats: A review of
the respective roles of the two olfactory systems. Horm Behav. 46, 257-271.
Gelez, H., and Fabre-Nys, C., 2006. Role of the olfactory systems and importance of
learning in the ewes' response to rams or their odors. Reprod Nutr Dev. 46, 401415.
Gentner, T. Q., and Hulse, S. H., 2000. Female European starling preference and choice
for variation in conspecific male song. Anim Behav. 59, 443-458.
Goritz, F., Neubauer, K., Naidenko, S. V., Fickel, J., and Jewgenow, K., 2006.
Investigations on reproductive physiology in the male Eurasian lynx (Lynx lynx).
Theriogenology. 66, 1751-1754.
Gosling, L. M., and Roberts, S. C., 2001. Scent-marking by male mammals: cheat-proof
signals to competitors and mates. Adv Stud Behav. 30, 169-218.
Green, W. C. H., and Rothstein, A., 2009. Persistent influences of birth date on
dominance, growth and reproductive success in bison. J Zool. 230, 177-186.
Grossman, C. J., 1984. Regulation of the immune system by sex steroids. Endocr Rev. 5,
435-455.
57
Haley, M. P., Deutsch, C. J., and Le Boeuf, B. J., 1994. Size, dominance and copulatory
success in male northern elephant seals, Mirounga angustirostris. Ani Behav. 48,
1249-1260.
Hart, B. L., and Jones, T., 1975. Effects of castration on sexual behavior of tropical male
goats. Horm Behav. 6, 247-258.
Hau, M., 2007. Regulation of male traits by testosterone: implications for the evolution of
vertebrate life histories. Bioessays. 29, 133-144.
Iwata, E., Wakabayashi, Y., Kakuma, Y., Kikusui, T., Takeuchi, Y., and Mori, Y., 2000.
Testosterone-dependent primer pheromone production in the sebaceous gland of
male goat. Biol Reprod. 62, 806-810.
Jainudeen, M. R., Katonogole, C. B., and Short, R. V., 1972. Plasma testosterone levels
in relation to musth and sexual activity in the male asiatic elephant, Elephas
maximus. J Reprod Fertil. 29, 99-103.
Jiguet, F., and Bretagnolle, V., 2001. Courtship behaviour in a lekking species: individual
variations and settlement tactics in male little bustard. Behav Proc. 55, 107-118.
Johnston, R. E., 1979. Olfactory preferences, scent marking, and "proceptivity" in female
hamsters. Horm Behav. 13, 21-39.
Johnston, R. E., 1981. Testosterone dependence of scent marking by male hamsters
(Mesocricetus auratus). Behav Neur Biol. 31, 96-99.
Karino, K., 1995. Male-male competition and female mate choice through courtship
display in the territorial damselfish Stegastes nigricans. Ethology. 100, 126-138.
Katz, L. S., 2007. Sexual behavior of domesticated ruminants. Horm Behav. 52, 56-63.
Ketterson, E. D., Nolan, V., Jr., Wolf, L., Ziegenfus, C., Dufty, A. M., Jr., Ball, G. F., and
Johnsen, T. S., 1991. Testosterone and avian life histories: the effect of
experimentally elevated testosterone on corticosterone and body mass in darkeyed juncos. Horm Behav. 25, 489-503.
Knapp, R. A., and Kovach, J. T., 1991. Courtship as an honest indicator of male parental
quality in the bicolor damselfish, Stegastes partitus. Behav Ecol. 2, 295.
Komers, P. E., and Dhindsa, M. S., 1989. Influence of dominance and age on mate choice
in black-billed magpies: an experimental study. Anim Behav. 37, 645-655.
Krebs, J. R., and Davies, N. B., 1978. Behavioural Ecology: An Evolutionary Approach.
Blackwell Scientific, Oxford, England.
Li, C., Jiang, Z., Jiang, G., and Fang, J., 2001. Seasonal changes of reproductive behavior
and fecal steroid concentrations in Père David's deer. Horm Behav. 40, 518-525.
Lincoln, G. A., Guinness, F., and Short, R. V., 1972. The way in which testosterone
controls the social and sexual behavior of the red deer stag (Cervus elaphus).
Horm Behav. 3, 375-396.
Manning, J. T., 1989. Age-advertisement and the evolution of the peacock's train. J
Evolution Biol. 2, 379-384.
Marit, G. B., Scheffrahn, N. S., Troxel, T. R., and Kesler, D. J., 1979. Sex behavior and
hormone responses in ewes administered testosterone propionate.
Theriogenology. 12, 375-381.
Marler, C. A., and Moore, M. C., 1989. Time and energy costs of aggression in
testosterone-implanted free-living male mountain spiny lizards (Sceloporus
jarrovi). Physiol Zool. 62, 1334-1350.
58
Marsh, J. A., and Scanes, C. G., 1994. Neuroendocrine-immune interactions. Poultry Sci.
73, 1049-1061.
McGinnis, M. Y., Christina Mirth, M., Zebrowski, A. F., and Dreifuss, R. M., 1989.
Critical exposure time for androgen activation of male sexual behavior in rats.
Physiol Behav. 46, 159-165.
Meyer, H. H. D., Sauerwein, H., and O'Callaghan, D., 1988. Possible regulation of
muscle growth via estrogen and androgen receptors. Eur J Endocrinol. 117, S189S190.
Minter, L. J., and DeLiberto, T. J., 2008. Seasonal variation in serum testosterone,
testicular volume, and semen characteristics in the coyote (Canis latrans).
Theriogenology. 69, 946-952.
Mougeot, F., Irvine, J. R., Seivwright, L., Redpath, S. M., and Piertney, S., 2004.
Testosterone, immunocompetence, and honest sexual signaling in male red
grouse. Behav Ecol. 15, 930-937.
Muduuli, D. S., Sanford, L. M., Palmer, W. M., and Howland, B. E., 1979. Secretory
patterns and circadian and seasonal changes in lutenizing hormone, follicle
stimulating hormone, prolactin and testosterone in the male pygmy goat. J Anim
Sci. 49, 543-553.
Ott, R. S.,Nelson, D. R., andHixon, J. E., 1980. Fertility of goats following
synchronization of estrus with prostagland in F2[alpha]. Theriogenology. 13, 341345.
Patricelli, G. L.,Uy, J. A. C.,Walsh, G., andBorgia, G., 2002. Sexual selection: male
displays adjusted to female's response. Nature. 415, 279-280.
Parrott, R. F., 1978. Courtship and copulation in prepubertally castrated male sheep
(wethers) treated with 17 [beta]-estradiol, aromatizable androgens, or
dihydrotestosterone. Horm Behav. 11, 20-27.
Perkins, A., and Roselli, C. E., 2007. The ram as a model for behavioral
neuroendocrinology. Horm Behav. 52, 70-77.
Peters, A., 2000. Testosterone treatment is immunosuppressive in superb fairy-wrens, yet
free-living males with high testosterone are more immunocompetent. Proc R Soc
Lond B. 267, 883-889.
Poole, J. H., 1989. Mate guarding, reproductive success and female choice in African
elephants. Anim Behav. 37, 842-849.
Poole, J. H., Kasman, L. H., Ramsay, E. C., and Lasley, B. L., 1984. Musth and urinary
testosterone concentrations in the African elephant (Loxodonta africana). J
Reprod Fertil. 70, 255-260.
Rasmussen, L. E., Riddle, H. S., and Krishnamurthy, V., 2002. Mellifluous matures to
malodorous in musth. Nature. 415, 975-976.
Rhen, T., and Crews, D., 2002. Variation in reproductive behaviour within a sex: neural
systems and endocrine activation. J Neuroendocrinol. 14, 517-531.
Riters, L. V., Eens, M., Pinxten, R., Duffy, D. L., Balthazart, J., and Ball, G. F., 2000.
Seasonal changes in courtship song and the medial preoptic area in male
European starlings (Sturnus vulgaris). Horm Behav. 38, 250-261.
Rivas-Munoz, R., Fitz-Rodriguez, G., Poindron, P., Malpaux, B., and Delgadillo, J. A.,
2007. Stimulation of estrous behavior in grazing female goats by continuous or
discontinuous exposure to males. J Anim Sci. 85, 1257-1263.
59
Sanford, L. M., Palmer, W. M., and Howland, B. E., 1977. Changes in the profiles of
serum LH, FSH and testosterone, and in mating performance and ejaculate
volume in the ram during the ovine breeding season. J Anim Sci. 45, 1382-1391.
Schulte, B. A., and Rasmussen, L. E. L. (1999). Musth, sexual selection, testosterone, and
metabolites. In R. E. Johnston, D. Muller-Schwarze, and P. W. Sorensen (Eds.),
Advances in Chemical Signals in Vetebrates, pp. 383-397. Kluwer
Academic/Plenum Publishers, New York.
Seymour, R. M., and Sozou, P. D., 2009. Duration of courtship effort as a costly signal. J
Theoret Bioly. 256, 1-13.
Signoret, J. P., 1970. Reproductive behaviour of pigs. J Reprod Fertility. Supplement. 11.
Taylor, G. T.,Haller, J., andRegan, D., 1982. Female rats prefer an area vacated by a high
testosterone male. Physiol Behav. 28, 953-958.
Thompson, C. W., Hillgarth, N., Leu, M., and McClure, H. E., 1997. High parasite load
in house finches (Carpodacus mexicanus) is correlated with reduced expression of
a sexually selected trait. American Naturalist. 149, 270-294.
Trivers, R. L. (1972). Parental investment and sexual selection. In: B. Campbell (Ed.),
Sexual Selection and the Descent of Man 1871-1971, pp. 136-179. Aldine Press,
Chicago.
Vinnedge, B., and Verrell, P., 1998. Variance in male mating success and female choice
for persuasive courtship displays. Anim Behav. 56, 443-448.
Waitt, C., Little, A. C., Wolfensohn, S., Honess, P., Brown, A. P., Buchanan-Smith, H.
M., andPerrett, D. I., 2003. Evidence from rhesus macaques suggests that male
coloration plays a role in female primate mate choice. Proc R Soc Lond B. 270,
S144-S146.
Walkden-Brown, S. W.,Restall, B. J., andHenniawati, 1993. The male effect in the
Australian cashmere goat. Role of olfactory cues from the male. Anim Reprod
Sci. 32, 55-67.
West, P. M., and Packer, C., 2002. Sexual selection, temperature, and the lion's mane.
Science. 297, 1339-1343.
Wingfield, J. C., 1984. Androgens and mating systems: testosterone-induced polygyny in
normally monogamous birds. Auk. 101, 665-671.
Winkler, L. A., 1989. Morphology and relationships of the orangutan fatty cheek pads.
American J Primat. 17, 305-319.
Wolff, J. O., 2004. Scent marking by voles in response to predation risk: a fieldlaboratory validation. Behav Ecol 15, 286-289.
Yahr, P., Newman, A., and Stephen, D. R., 1979. Sexual behavior and scent marking in
male gerbils: Comparison of changes after castration and testosterone
replacement. Horm Behav. 13, 175-184.
Zahavi, A., 1975. Mate selection-a selection for a handicap. J Theor Biol. 53, 205-214.
Zuk, M., 1988. Parasite load, body size, and age of wild-caught male field crickets
(Orthoptera: Gryllidae): effects on sexual selection. Evolution. 42, 969-976.
60
CHAPTER III
FEMALE GOATS USE COURTSHIP DISPLAY AS AN HONEST
INDICATOR OF A MALE’S FITNESS
61
ABSTRACT
Due to the differential cost of reproduction in promiscuous species, like the
domesticated goat (Capra hircus), it is expected that females should mate with higher
quality males, while males should mate with a greater number of females. Females may
use extravagant secondary sexual characteristics of males such as courtship display to
distinguish among high and low quality males. Since testosterone (T) controls a large
suite of secondary sexual characteristics, variation in T concentrations may account of
differences in courtship rates. Two studies were conducted to examine the relationship
between T concentrations and courtship rate and its role in mammalian female mate
choice. Experiment 1 bucks (intact males) were studies and in Experiment 2 T-replaced
wethers (castrated pre-pubertally) were used that received oil vehicle control (CON), or
25 mg, or 100 mg testosterone propionate (TP) injections. For both studies, mean
courtship rates and circulating T concentrations were determined. T concentrations and
courtship rate were positively correlated for bucks. Males receiving 25 mg and 100 mg
TP courted females at a similar rate, but both were significantly higher than courtship
rates of the CON wethers (P<.01). When females were given a choice between the high
and low courting bucks, females preferred the high courting buck (P<.001). Females did
not show a preference for either the 100 mg or 25 mg TP-treated wethers, however both
were preferred in comparison to the CON wethers (P<.001). Taken together, these studies
suggest that courtship rate is T-dependent in goats. Further, females can use courtship
rate to distinguish among high and low quality males.
Key Words: Courtship, Female Choice, Evolution
62
INTRODUCTION
Extravagant secondary sexual characteristics such as bright coloration, scent
marking, and courtship cues have all received considerable attention in the study of
sexual selection. Trivers (1972) proposed that in species in which there is greater
maternal investment compared to paternal investment, females should breed with higher
quality males while males should breed with a greater quantity of females. In this
context, extravagant secondary sexual characteristics may not be arbitrary, but rather
serve as an indicator of a males’ reproductive fitness. According to Zahavi’s handicap
principle, the cost of the characteristic should be directly related to the reliability of the
indicator or cue (Zahavi, 1975; 1977). Consequently, secondary sexual characteristics
serve as an honest indicator of the male’s fitness with high quality males displaying more
extravagant secondary sexual characteristics than those who are lower quality (reviewed
in (Andersson, 1994). Females who mate with highly fit individuals benefit directly by
increasing their reproductive fitness. Thus, secondary sexual characteristics may play an
important role in a female’s mate preference
Male courtship is often accompanied by visual ornamentation such as that seen in
feathers of a peacock (Petrie et al., 1991) or swallow (Møller, 1988), or intense coloration
such as that displayed by stickleback fish (Bakker, 1993). Courtship may also be
accompanied by vocalizations such as roars of red deer (Charlton et al., 2007; McComb,
1991), and courtship vocalizations by the satin bowerbird (Loffredo and Borgia, 1986)
and marginated tortoises (Sacchi et al., 2003). Both visual and auditory cues may aid in
female mate choice by further exaggerating courtship cues displayed by the male
(McLintock and Uetz, 1996). However, for this paper, we will focus on courtship display
63
only and in this context we define courtship as male stereotypical, repetitious behaviors
which occur toward the female prior to mating.
If females use courtship cues to distinguish among high and low quality males,
then sexual selection pressures should give rise to variation among males’ courtship
displays. Male courtship rate and frequency of courtship display are sexually selected
characteristics that have been well studied in birds (Jiguet and Bretagnolle, 2001;
Patricelli et al., 2002), fish (Knapp and Kovach, 1991; Vinnedge and Verrell, 1998), and
amphibians (Karino, 1995), with higher performing males being preferred by females.
One explanation for this preference for higher performing males is that such displays may
provide information to the female about the male’s quality, and thus, her potential fitness
gains. Studies using several avian species suggest that male courtship display may be an
honest indicator of a male’s age (Loffredo and Borgia, 1986), experience (Yasukawa,
1981), and/or body condition (Genevois and Bretagnolle, 1994; Simmons, 1988). Male
courtship may provide evidence of a male’s genetic quality as demonstrated by studies on
reptiles (Galeotti et al., 2005) and birds (Hamilton and Zuk, 1982; Hardouin et al., 2009;
Jiguet and Bretagnolle, 2001; Martín-Vivaldi et al., 1999). Further, courtship may
provide information about a male’s parental ability as displayed by birds (Buchanan and
Catchpole, 2000) and fish (Knapp and Kovach, 1991; Takahashi and Kohda, 2004).
Testosterone (T) often plays a key role in regulating male-typical reproductive
behaviors including courtship behavior (reviewed in: Hau, 2007; Rhen and Crews, 2002).
High T concentrations impose energetic costs (Buchanan et al., 2001; Wingfield et al.,
2001) and immune suppression (Marsh, 1992; Marsh and Scanes, 1994) to male birds;
preventing a male from falsely advertising his fitness status. Testosterone concentrations
64
may be an honest indicator of a male’s fitness and resulting T-dependent behaviors such
as courtship may be used as a cue to assess fitness. Consequently, a relationship between
male quality and T concentrations exists as high quality males invest in courtship display
to gain access to mates while low quality males invest in survival (Duckworth et al.,
2001; Folstad and Karter, 1992). Testosterone replacement studies using birds (Mougeot
et al., 2004; Takahashi and Kohda, 2004) have provided unique opportunities to
investigate the relationship between testosterone concentrations, courtship,
immonosuppression, and body condition, providing inference and comparisons to wild
populations.
Little is known about courtship and its role in mammalian female mate choice;
however we do know that courtship displays are common in the majority of ungulate
species (reviewed in: Walther, 1984) and are often displayed exclusively during the
breeding season. The domesticated male goat also displays courtship behaviors during the
breeding season including a foreleg kick, head-twist and nudge, and tongue flick. Upon
encountering a female, a male will generally first display a foreleg kick whereby the male
locks his front legs and strikes the female with his hoofs or foreleg. If the female does not
run away, the male may follow the foreleg kick with a head-twist and nudge, and tongue
flick, which are done simultaneously. Display of the tongue flick results in a gobble
sound. The male will repeat these behaviors until he mounts the female. The display of
courtship behavior by the domesticated goat suggests that the goat will serve as an
excellent model for the study of courtship behavior, honesty and female mate choice. To
examine courtship and female mate choice, two experiments were designed with
Experiment 1 using gonadally-intact males (bucks; Experiment 1) and Experiment 2
65
using pre-pubertally castrated males (wethers) supplemented with testosterone. The
objectives of both experiments were twofold. The first objective was to examine the
correlation between courtship rate and T concentrations. The second objective was to test
if females are able to use courtship cues to distinguish among males that court females at
different rates. It is predicted that male courtship behavior is T-dependent and females
will prefer high courting males.
66
MATERIALS AND METHODS
Animals
All animals were Alpine goats between the ages of 1.5-9 years which received a
diet consisting of grass hay and grain, and had ad libitum access to water and mineral salt
blocks. Diet and husbandry was in compliance with the Consortium Guide for the Care
and Use of Agricultural Animals in Agricultural Research and Education (FASS, 2010).
Research was conducted as approved by the Rutgers University Animal Care and
Facilities Committee. Male and female goats were housed on the NJ Agricultural
Experiment Station Research Farm in New Brunswick, NJ (40° 29' 10" N / 74° 27' 8" W)
in barns with free access to outdoor exercise areas. The breeding season for the Alpine
goat begins in mid-August and terminates near the end of January in the northern
hemisphere. Focal goats were estrous-synchronized females. Males used for courtship
rate test and as goal males for the preference tests were in various reproductive states.
Estrous Synchronization and Detection
Focal goats were estrous-synchronized females drawn from a herd of 24. The herd
was divided into two groups which were estrus-synchronized on alternating weeks.
Estrous synchronization was accomplished using a sequential treatment of prostaglandin
(PGF 2α ). During the breeding season, each female received two injections of 10 mg
PGF 2α (dinoprost tromethamine, i.m.) at 11 or 14 days prior and 51 hours prior to the
behavior test as modified from Ott et al. (1980). For experiments conducted using
ovariectomized (OVX) females, estrus was induced by providing exogenous progestins
and estradiol (Billings and Katz 1997; 1999).
67
Standing estrus was detected prior to each preference test. A non-experimental buck was
brought into the females’ home pen and allowed to mount females but not allowed to
intromit. If the female stood to be mounted, she was considered to be in estrus. If the
female rejected the male, she was considered non-estrous. All females, regardless of
estrous state, were tested in the behavior experiment; however, only data from estrous
females are reported.
Blood Sampling and Radioimmunoassay (RIA)
Blood samples were collected for both Experiments 1 and 2 via jugular
venipuncture. For Experiment 1, blood samples were collected from bucks on a weekly
basis (September through December) at 0800. For Experiment 2, blood samples were
collected once from the TP-treated males over a 48-hr time period at the following time
points relative to the injection of TP: 0, 0.25, 0.5, 1, 2, 6, 12, 24, and 48 h. Serum was
stored at -20 °C until assayed.
Serum testosterone concentrations were determined by commercial RIA kit
validated in our laboratory for goat serum (bucks: Beckman Coulter DSL-4000, Webster,
TX; TP-treated wethers: Siemens Healthcare Diagnostics, Inc., Coat-A-Count Total
Testosterone, Los Angeles, CA). The minimum detection limit of the DSL-4000 assay
was 0.02 ng/ml and the inter-assay coefficient of variation was 12%. The minimum
detection limit of the Coat-A-Count Total Testosterone assay was 0.002 ng/ml and the
inter-assay coefficient of variation was 9%.
Male Courtship Rate Test
The order in which the males were tested was randomly assigned. All testing
began at 0800. Prior to the start of the male courtship rate test, two estrous OVX females
68
were placed within the holding pen in the test apparatus (Fig. 1) and remained there for
the duration of the testing period. Males were tested individually. Each trial was 10 min
in duration, during which total number of courts (head-twist and nudge, and tongue flick)
and foreleg kicks were measured.
Partner Preference Testing
Females were acclimated to the test apparatus (Fig. 2) for two weeks prior to the
behavior test. Trials commenced once all females showed no signs of stress (e.g.,
vocalizing, jumping) while in the test apparatus.
Prior to the start of each behavior test, a male was placed within each holding pen
at both ends of the test apparatus and remained there for the duration of the trial. To
account for any side biases in Experiment 1, a switchback design was used. Accordingly,
females were placed in the test apparatus for two trials. During each trial, one estrous
female was led to the center of the neutral zone and released. She was allowed to travel
the test apparatus for 5 min. Use of a 5-min trial period was determined after observation
of estrous females within the test apparatus. Preference trials lasting longer than 5 min,
resulted in females becoming agitated. Total time spent in the incentive zone near each
male was recorded for each trial. For the switch back, males were removed from the
holding pen on one end of the test apparatus and placed in the holding pen on the
opposite end of the test apparatus. Females were then re-tested the same day using the
above protocol.
Prior to Experiment 2, it was determined that a switchback design was
unnecessary as females did not display a side bias in the test apparatus. Accordingly, each
female was tested only once in Exp 2.
69
Statistical Analysis
Serum T concentrations: For bucks, mean serum T concentrations were
determined from samples taken September through December. For TP-treated wethers, T
concentrations are represented as area under the curve (AUC) for the 48-hr collection.
Differences among T concentrations in TP-treated wethers were compared with a oneway ANOVA, and results were deemed significant at P<0.05 (SAS Version 9.2, Cary,
NC).
Courtship rate: Courtship rate was determined by summing total number of
foreleg kicks and courts during each courtship rate test. Mean courtship rate for each
individual was determined using data from all courtship rate tests. A linear regression
analysis of courtship rate versus T concentration was completed and results were deemed
significant at P<0.05 (Sigma Plot 10, San Jose, CA). For the TP-treated wethers, a oneway ANOVA was completed for the effects of T dose on courtship rate, and results were
deemed significant at P<0.05 (SAS Version 9.2, Cary, NC).
Preference Tests: A female’s preference for a particular male (e.g. high-courting
buck versus low-courting buck) was computed by calculating a preference score as
follows:
In Experiment 1, for each female the preference scores for a particular male from the two
trials were averaged. In Experiment 2, there was only one trial. Preference scores were
determined to be different from chance (50%) using a binomial test. Variation in
70
preference scores is reported as standard error of the proportion (± SEP). Results were
deemed significant at P<0.05 (NCSS Statistical Software, 2001, Kaysville, UT).
Experiment 1:
To examine if courtship rate is a T dependent behavior, courtship rate and blood
samples were collected from six bucks in 2008 and seven bucks in 2009 for a total of 13
different males. Courtship rate was measured on four dates in 2008 and five dates in
2009. Preference tests were conducted in 2008 to determine if females can use courtship
rates to distinguish among males. A total of 21estrous females were tested between two
dates. The buck with the highest rate of courting (mean of 157 courts/10 min) and the
buck with the lowest rate of courting (mean of 42 courts/10 min) were used for all
preference tests.
Experiment 2:
Courtship rate was also examined in wethers receiving testosterone replacement.
Wethers were randomly assigned to one of three testosterone propionate (TP; A7000-000
Steroids, Inc. Newport, RI) treatment groups: oil vehicle control (CON; n=3), 25 mg TP
(n=5), or 100 mg TP (n=5). TP-treated males received TP (s.c.) 3x/week beginning
August 3. Research from previous studies by our laboratory have shown that 25 mg TP is
sufficient to activate male reproductive behaviors in castrated male goats (Longpre and
Katz, In Press). Injections continued for a total of 24 wk. Courtship rate was measured
for all wethers on five dates.
Preference tests were conducted to determine if females can use courtship rate to
distinguish among the three treatment groups. The following preference tests were
compared and number of estrous females used is indicated: CON vs 25 mg TP-treated
71
wether (n=10); 25 mg vs 100 mg TP-treated wether (n=9); CON vs 100 mg TP-treated
wether (n=5). One male from each of the treatment groups (CON, 25 mg, and 100 mg)
was chosen at random and used for each of the female partner preference tests.
72
RESULTS
Experiment 1
To test if serum T concentrations and courtship rate are related in bucks, serum T
concentrations and courtship rate for a total of 13 bucks was measured and is depicted in
Figure 3. Mean serum T concentrations and mean courtship rate were positively
correlated (r2= 0.67, P<0.05).
Estrous females were given a choice between a high and low courting buck. Mean
preference scores for high versus low courting rate buck are presented in Figure 4.
Estrous females demonstrated a significant preference for the high courting rate male
(P<0.001).
Experiment 2
To further examine the relationship between circulating T concentrations and
courtship rate, courtship rate was measured for three groups of wethers treated with
different TP doses and is presented in Figure 5. Serum T concentrations, represented as
area under the curve (AUC), were significantly different for all three treatment groups
with the 100 mg TP-treated wethers having the highest T concentrations followed by the
25 mg TP-treated wethers (P<.0001; Fig 5). The CON wethers showed no courtship
behaviors and courtship rate was significantly different from the 25 mg and 100 mg TPtreated wethers (P<.01; Fig 5). Courtship rate among males receiving the same dose of
TP showed little variance.
Mean preference scores from choice tests performed with TP-treated wethers are
presented in Figure 6. Estrous female subjects demonstrated a significant preference for
25 mg and 100 mg TP-treated wethers compared to the CON wether (P<.001; Fig. 6).
73
Estrous female subjects demonstrated no preference between the wethers treated with 25
mg and 100 mg TP (Fig. 6).
74
DISCUSSION
These studies demonstrated that T concentrations and courtship rate are correlated
in male goats. Further, estrous females prefer males that court females at a higher rate
than those that court females at a lower rate. These data agree with findings in several
bird species (reviewed in: Ball and Balthazart, 2004), however this study is the first to
find a positive correlation between courtship display and androgens in male ruminants
(reviewed in: Katz, 2007; Perkins and Roselli, 2007). Bucks with higher T concentrations
courted females at a higher rate than those with lower T concentrations. The divergence
in courtship rate between the high and low courting bucks was consistent during every
male courtship rate test. Specifically, the highest courting buck courted at a higher
courtship rate while the lowest courting buck always courted at the lowest rate for all
courtship rate tests. Serum T concentrations were also consistently higher for the high
courting buck and lower for the low courting buck for every sample taken during the
breeding season, further supporting the strength of the correlation between courtship rate
and T concentrations.
Experiment 2 further confirmed that courtship rate is T-dependent. The CON
wethers displayed no courtship behavior while the 25 mg and 100 mg TP-treated wethers
displayed significantly higher courtship rates. Courtship rates among males receiving the
same dose of TP were highly consistent. Lack of change in courtship display between the
25mg and 100mg TP-treated wethers may also be due to both groups exceeding a
threshold concentration of T required to display high courtship rates. After threshold T
concentrations are achieved, increases in T concentrations will have nominal effects on
courtship rate. To examine the expression courtship behavior and androgen
75
concentrations, Fusani and Hutchison (2003) implanted male ring doves with either
single or double T implants and measured T and dihydrotestosterone (DHT)
concentrations, as well as measuring courtship behavior. Males with two implants had
significantly higher T and DHT concentrations compared to males with a single implant,
however there was no difference in courtship behavior displayed by the two groups of
males. Similar threshold responses to sexual behavior have also been found in rats and
sheep suggesting that this phenomenon may be present in multiple species. Damassa et
al. (1977) measured sexual behavior of castrated male rats provided T implants. Males
receiving T implants producing at least 25% of the normal T concentrations of an intact
male or greater showed no significant differences in reproductive behaviors displayed.
However, it was observed that intromission frequencies were decreased and there were
longer initiation latencies. D'Occhio and Brooks (1982) reported that castrated sheep
dosed with 1-2mg TP/day displayed mounting behavior. Dosing with 4mg TP/day was
required for a complete mating response. Taken together, these studies suggest that T
concentrations above threshold may be required for successful copulations, but not for
courtship display. If there is a T response threshold in goats, the results from the study
reported here suggest it is at or below T concentrations that were achieved with the 25mg
TP dose. However to confirm a threshold effect, a more rigorous testing using lower
doses of T will be required.
Due to the costs of maintaining high T concentrations, it is unlikely that selection
pressures would drive preference for males with high T concentrations unless there is
some advantage (Fisher and Bennett, 1999). During the male courtship rate test it was
observed that low courting males would court females intensely for the first few minutes
76
of the test and then stop while the high courting males courted intensely for the entire
duration of the behavior test. As previously suggested from findings by D'Occhio and
Brooks (1982) and Damassa et al. (1977), it is likely that high testosterone males would
be able to court females for a longer duration of time or display a larger repertoire of
behaviors, keeping females in close vicinity and obtaining multiple copulations. In
obtaining multiple copulations, a male increases his likelihood of siring a greater number
of offspring. Feder et al. (1977) proposed that high T concentrations may serve to initiate
additional, more costly courtship behaviors to be displayed by the male which accelerate
ovulation by the female. Perkins and Fitzgerald (1994) exposed anestrous ewes to rams
exhibiting either high (HP) or low (LP) levels of sexual performance. HP males courted
more ewes on the first day and spent more time with ewes over the 28 d experiment.
Ewes exposed to HP males tended to ovulate earlier and greater percentage of ewes
ovulated after exposure to the HP males in comparison to ewes exposed to the LP males.
It is not clear whether females are able to delay estrus until a male with high T
concentrations (high quality) is present, increasing her reproductive fitness; or if high
quality males are able to induce ovulation as a means of mating with a greater quantity of
females improving reproductive fitness. In either case, high T males benefit by obtaining
more copulations, and likely producing more offspring.
Sexual selection appears to be potentially important in explaining the variation in
courtship rates among males. Courtship display may serve as an honest indicator of a
male’s fitness, thus high courting males should be preferred over lower courting males.
When estrous females were given a choice between the high and low courting males in
both Experiments 1 and 2, females were able to distinguish between and show preference
77
for the high courting male. Preference for courting males has been found in several nonmammalian species, for example: lizards (Kelso and Martins, 2008), wolf spiders
(Kotiaho et al., 1996), fiddler crabs (Murai and Backwell, 2006; Oliveira and Custodio,
1998), and salamanders (Vinnedge and Verrell, 1998). Females showed no preference
between the 25 mg and 100 mg TP-treated wethers and this may be due to courtship rates
between these males being similar. An alternative explanation for this lack of preference
is that both males meet the criteria of a high quality male, thus preference for one male
over another is unnecessary. This alternative explanation supports the previously
mentioned T concentration threshold response. Males that meet or exceed threshold T
concentrations and display courtship behaviors accordingly, are considered to be high
quality compared to those that do not meet threshold T concentrations.
Results from this study indicate that females use courtship rate to distinguish
among males. However, it is possible that females may be using multiple T-dependent
cues, in addition to courtship when assessing males. Use of multiple cues would, likely,
decrease the possibility of females making mate choice errors. During partner preference
testing females were presented with males that courted at different rates. Males may have
also been providing females with additional T-dependent cues including morphological
or chemical cues. Studies from our lab indicate that male morphology is not used by
females for mate choice (Longpre and Katz, In Press). Gosling and Roberts (2001) argue
that chemical cues provided by males may be an honest indicator of fitness. In support of
this argument, in several rodent species, females are able to distinguish between and
show preference for particular males using chemical cues alone (Drickamer, 1989;
Hoffmeyer, 1982; Penn and Potts, 1998; Penn, 2002; Rich and Hurst, 1998; 1999). Iwata
78
et al. (2000; 2001) found that male goat sebaceous gland size and pheromone activity are
T-dependent. Thus, females may use chemical cues provided by male goats in
conjunction with courtship cues, to distinguish among high and low quality males.
In summary, males with higher T concentrations court females at a higher rate
than those with lower T concentrations and female prefer high courting males. Serum T
concentrations may be an honest indicator of fitness, thus females can distinguish
between high and low quality males via courtship cues provided by the male. This being
the case, females that distinguish among and show preference for high courting males
should obtain fitness benefits. It is unknown if there is a threshold effect, a more rigorous
testing using lower doses of T will be required and warrants further investigation.
ACKNOWLEDGEMENTS
We would like to acknowledge Susan E. Becker for her excellent technical
assistance. We would also like to thank our Animal Science undergraduate students who
helped conduct this research. This work was supported by NJ Agricultural Experiment
Station, project 06144.
79
Figure 1
Figure 1. Male courtship rate test apparatus: Apparatus contained a holding pen.
80
Figure 2
Figure 2. Test apparatus for female preference test paradigm: The apparatus was
divided in the middle by a 11.6 m neutral zone. The neutral zone was defined by chalk
lines on the floor that ran up the wall on each side of the test apparatus. Each incentive
zone contained a holding pen.
81
Figure 3
Mean Court Rate (Courts/10min)
350
300
250
200
150
100
50
0
7
8
9
10
11
12
13
Mean T Concentrations (ng/ml)
Figure 3. Male courtship rate and T concentrations are correlated: Mean serum
testosterone (T) concentrations versus mean courtship rate for 13 bucks (r2= 0.67,
P<0.05).
82
Figure 4
100
Preference Score (%)
80
*
60
40
20
0
High Courting Buck Low Courting Buck
Figure 4. Estrous females prefer high courting bucks: Mean (± SEP) preference score
of 21 estrous females during 5-min partner preference test for a high-courting buck vs a
low-courting buck during the breeding season. * Significant difference (P<0.001).
83
Figure 5
250
50
γ
T Concentrations
Courtship Rate
b
200
40
b
150
30
100
20
β
50
10
α, a
0
Mean Courtship Rate (Courts/10 min)
Mean Serum T Concentrations
Area Under Curve (ug min ml-1)
60
0
CON
25 mg
100 mg
n=3
n=5
n=5
TP-Treated Wethers
Figure 5. Courtship rate and T concentrations for TP-treated Wethers: Mean (±
SEM) serum T concentrations and mean (± SEM) courtship rate for TP-treated wethers.
Testosterone (T) concentrations are represented as area under the curve for 48-hr
collection. a, b Mean courtship rates with different subscripts differ (P< 0.01). α, β, γ Mean
T concentrations with different subscripts differ P< 0.0001).
84
Figure 6
Preference Score (%)
*
*
100
80
60
40
20
(n= 10)
(n = 5)
25
m
10 g
0
m
g
C
O
10 N
0
m
g
g
m
25
C
O
N
0
(n= 9)
TP-treated Wether Choices
Figure 6. Estrous females prefer TP-treated wethers that court at higher rates:
Mean (± SEP) preference score during 5-min partner preference tests during the breeding
season. Number of estrous females varied for each preference test and is indicated. *
Significant difference (P<0.001).
85
REFERENCES
Andersson, M., 1994. Sexual Selection. Princeton University Press, Princeton.
Bakker, T. C. M., 1993. Positive genetic correlation between female preference and
preferred male ornament in sticklebacks. Nature. 363, 255-257.
Ball, G. F., and Balthazart, J., 2004. Hormonal regulation of brain circuits mediating
male sexual behavior in birds. Physiol Behav. 83, 329-346.
Billings, H. J., and Katz, L. S., 1997. Progesterone Facilitation and Inhibition of
Estradiol-Induced Sexual Behavior in the Female Goat. Horm Behav. 31, 47-53.
Billings, H. J., and Katz, L. S., 1999. Facilitation of sexual behavior in French-Alpine
goats treated with intravaginal progesterone-releasing devices and estradiol during
the breeding and nonbreeding seasons. J Anim Sci. 77, 2073-2078.
Buchanan, K. L., and Catchpole, C. K., 2000. Song as an indicator of male parental effort
in the sedge warbler. Proc R Soc B. 267, 321-326.
Charlton, B. D., Reby, D., and McComb, K., 2007. Female red deer prefer the roars of
larger males. Bio Lett-UK. 3, 382-385.
D'Occhio, M. J., and Brooks, D. E., 1982. Threshold of plasma testosterone required for
normal mating activity in male sheep. Horm Behav. 16, 383-394.
Damassa, D. A., Smith, E. R., Tennent, B., and Davidson, J. M., 1977. The relationship
between circulating testosterone levels and male sexual behavior in rats. Horm
Behav. 8, 275-86.
Drickamer, L. C., 1989. Odor preferences of wild stock female house mice (Mus
domesticus) tested at three ages using urine and other cues from conspecific males
and females. J Chem Ecol. 15, 1971-1987.
Duckworth, R. A., Mendonca, M. T., and Hill, G. E., 2001. A condition dependent link
between testosterone and disease resistance in the house finch. Proc Biol Sci. 268,
2467-72.
FASS, 2010. Guide for the care and use of agricultural animals in research and
teaching, 3rd ed. Fed. Anim Sci Soc., Champagne, IL.
Feder, H. H., Storey, A., Goodwin, D., Reboulleau, C., and Silver, R., 1977. Testosterone
and" 5 -Dihydrotestosterone" Levels in Peripheral Plasma of Male and Female
Ring Doves (Streptopelia risoria) During the Reproductive Cycle. Biol Reprod.
16, 666-677.
Fisher, S. R. A., and Bennett, J. H., 1999. The genetical theory of natural selection: a
complete variorum edition. Oxford University Press, USA.
Folstad, I., and Karter, A. J., 1992. Parasites, bright males, and the immunocompetence
handicap. Am Nat. 139, 603-622.
Fusani, L., and Hutchison, J. B., 2003. Lack of changes in the courtship behaviour of
male ring doves after testosterone treatment. Ethol Ecol Evol. 15, 143-157.
Galeotti, P., Sacchi, R., Fasola, M., Rosa, D. P., Marchesi, M., and Ballasina, D., 2005.
Courtship displays and mounting calls are honest, condition-dependent signals
that influence mounting success in Hermann's tortoises. Can J Zoolog. 83, 13061313.
Genevois, F., and Bretagnolle, V., 1994. Male blue petrels reveal their body mass when
calling. Ethol Ecol Evol. 6, 377-383.
86
Gosling, L. M., and Roberts, S. C., 2001. Scent-marking by male mammals: cheat-proof
signals to competitors and mates. Adv Stud Behav. 30, 169-218.
Hamilton, W. D., and Zuk, M., 1982. Heritable true fitness and bright birds: a role for
parasites? Science. 218, 384-387.
Hardouin, L. A., Bretagnolle, V., Tabel, P., Bavoux, C., Burneleau, G., and Reby, D.,
2009. Acoustic cues to reproductive success in male owl hoots. Anim Behav. 78,
907-913.
Hau, M., 2007. Regulation of male traits by testosterone: implications for the evolution of
vertebrate life histories. BioEssays. 29, 133-144.
Hoffmeyer, I., 1982. Responses of female bank voles (Clethrionomys glareolus) to
dominant vs subordinate conspecific males and to urine odors from dominant vs
subordinate males. Behav Neural Biol. 36, 178-188.
Iwata, E., Wakabayashi, Y., Kakuma, Y., Kikusui, T., Takeuchi, Y., and Mori, Y., 2000.
Testosterone-dependent primer pheromone production in the sebaceous gland of
male goat. Biol Reprod. 62, 806-810.
Iwata, E., Wakabayashi, Y., Matsuse, S., Kikusui, T., Takeuchi, Y., and Mori, Y., 2001.
Induction of primer pheromone production by dihydrogentestosterone in the male
goat. J Vet Med Sci. 63, 347-348.
Jiguet, F., and Bretagnolle, V., 2001. Courtship behaviour in a lekking species: individual
variations and settlement tactics in male little bustard. Behav Process. 55, 107118.
Karino, K., 1995. Male-male competition and female mate choice through courtship
display in the territorial damselfish Stegastes nigricans. Ethology. 100, 126-138.
Katz, L. S., 2007. Sexual behavior of domesticated ruminants. Horm Behav. 52, 56-63.
Kelso, E. C., and Martins, E. P., 2008. Effects of two courtship display components on
female reproductive behaviour and physiology in the sagebrush lizard. Anim
Behav. 75, 639-646.
Knapp, R. A., and Kovach, J. T., 1991. Courtship as an honest indicator of male parental
quality in the bicolor damselfish, Stegastes partitus. Behav Ecol. 2, 295-300.
Kotiaho, J., Alatalo, R. V., Mappes, J., and Parri, S., 1996. Sexual selection in a wolf
spider: male drumming activity, body size, and viability. Evolution. 50, 19771981.
Loffredo, C. A., and Borgia, G., 1986. Male courtship vocalizations as cues for mate
choice in the satin bowerbird (Ptilonorhynchus violaceus). Auk. 103, 189-195.
Longpre, K. M., and Katz, L. S., In Press. Esrous female goats use testosteronedependent cues to assess mates. Horm Behav. doi:10.1016/j.yhbeh.2010.10.014
Marsh, J. A., 1992. Neuroendocrine- immune interactions in the avian species: a review.
Poultry Sci. 4, 129-167.
Marsh, J. A., and Scanes, C. G., 1994. Neuroendocrine-immune interactions. Poultry Sci.
73, 1049.
Martín-Vivaldi, M., Palomino, J. J., Soler, M., and Martínez, J. G., 1999. Song strophelength and reproductive success in a non-passerine bird, the Hoopoe Upupa
epops. Ibis. 141, 670-679.
McComb, K. E., 1991. Female choice for high roaring rates in red deer, Cervus elaphus.
Anim Behav. 41, 79-88.
87
McLintock, W. J., and Uetz, G. W., 1996. Female choice and pre-existing bias: visual
cues during courtship in twoSchizocosawolf spiders (Araneae: Lycosidae). Anim
Behav. 52, 167-181.
Møller, A. P., 1988. Female choice selects for male sexual tail ornaments in the
monogamous swallow. Nature. 332, 640-642.
Mougeot, F., Irvine, J. R., Seivwright, L., Redpath, S. M., and Piertney, S., 2004.
Testosterone, immunocompetence, and honest sexual signaling in male red
grouse. Behav Ecol. 15, 930-937.
Murai, M., and Backwell, P. R. Y., 2006. A conspicuous courtship signal in the fiddler
crab Uca perplexa: female choice based on display structure. Behav Ecol
Sociobiol. 60, 736-741.
Oliveira, R. F., and Custodio, M. R., 1998. Claw size, waving display and female choice
in the European fiddler crab, Uca tangeri. Ethol Ecol Evol. 10, 241-251.
Ott, R. S., Nelson, D. R., and Hixon, J. E., 1980. Fertility of goats following
synchronization of estrus with prostagland in F2[alpha]. Theriogenology. 13, 341345.
Patricelli, G. L., Uy, J. A. C., Walsh, G., and Borgia, G., 2002. Sexual selection: male
displays adjusted to female's response. Nature. 415, 279-280.
Penn, D., and Potts, W. K., 1998. Chemical singnals and parasite-mediated sexual
selection. Trends Ecol Evol. 13, 931-396.
Penn, D. J., 2002. The scent of genetic compatiblility: Sexual selection and the major
histocompatility complex. Ethology. 108, 1-21.
Perkins, A., and Fitzgerald, J. A., 1994. The behavioral component of the ram effect: the
influence of ram sexual behavior on the induction of estrus in anovulatory ewes. J
Anim Sci. 72, 51-55.
Perkins, A., and Roselli, C. E., 2007. The ram as a model for behavioral
neuroendocrinology. Horm Behav. 52, 70-77.
Petrie, M., Tim, H., and Carolyn, S., 1991. Peahens prefer peacocks with elaborate trains.
Animl Behav. 41, 323-331.
Rhen, T., and Crews, D., 2002. Variation in reproductive behaviour within a sex: neural
systems and endocrine activation. J Neuroendocrinol. 14, 517-531.
Rich, T. J., and Hurst, J. L., 1998. Scent marks as reliable signals of the competitive
ability of mates. Anim Behav. 56, 727-735.
Rich, T. J., and Hurst, J. L., 1999. The competing countermarks hypothesis: reliable
assessment of competitive ability by potential mates. Anim Behav. 58, 10271037.
Sacchi, R., Galeotti, P., Fasola, M., and Ballasina, D., 2003. Vocalizations and courtship
intensity correlate with mounting success in marginated tortoises Testudo
marginata. Behav Ecol Sociobiol. 55, 95-102.
Seymour, R. M., and Sozou, P. D., 2009. Duration of courtship effort as a costly signal. J
Theor Biol. 256, 1-13.
Simmons, R., 1988. Honest advertising, sexual selection, courtship displays, and body
condition of polygynous male harriers. Auk. 105, 303-307.
Takahashi, D., and Kohda, M., 2004. Courtship in fast water currents by a male stream
goby (Rhinogobius brunneus) communicates the parental quality honestly. Behav
Ecol Sociobiol. 55, 431-438.
88
Trivers, R. L. (1972). Parental investment and sexual selection. In B. Campbell (Ed.),
Sexual Selection and the descent of man 1871-1971 pp. 136-179. Aldine Press,
Chicago.
Vinnedge, B., and Verrell, P., 1998. Variance in male mating success and female choice
for persuasive courtship displays. Anim Behav. 56, 443-448.
Walther, F. R., 1984. Communication and expression in hoofed mammals. Indiana Univ
Pr.
Yasukawa, K., 1981. Male quality and female choice of mate in the red-winged blackbird
(Agelaius phoeniceus). Ecology. 922-929.
Zahavi, A., 1975. Mate selection-a selection for a handicap. J Theor Biol. 53, 205-14.
Zahavi, A., 1977. The cost of honesty (further remarks on the handicap principle). J
Theor Biol. 67, 603-5.
89
CHAPTER IV
SCENT OF A BUCK: DO MALES
ADVERTISE FITNESS VIA OLFACTORY CUES?
90
ABSTRACT
In promiscuous species such as the domesticated goat (Capra hircus), it is
expected that females should mate with higher quality males due to the differential cost
of reproduction. Females may utilize extravagant secondary sexual characteristics such as
chemical cues to distinguish among and mate exclusively with high quality mates.
Chemical cues found in urine or secreted from sebaceous glands are distributed into the
environment and have been directly associated with a male’s reproductive state,
specifically testosterone (T) concentrations. Variation in serum T concentrations among
males may account of differences in chemical cues provided. Two studies were
conducted to test whether a female’s preference for male chemical cues is correlated with
male T concentrations. For both experiments blood samples were taken from all of the
males. Rags were rubbed on males in different reproductive states: Bucks (intact male,
buck-scented rags), wether (castrated male, wether-scented rags). Control rags contained
no goat odors. For Experiment 1, females were given a choice between buck-scented
versus wether-scented rags and buck-scented versus control rags. Bucks had higher T
concentrations than wethers (P<.001) and females display a significant preference for the
buck scented rags (P<.001). For Experiment 2, females were given a choice between rags
rubbed on male’s house near females (Near buck-scented rags) or housed away from
females (Far buck-scented rags). The Near bucks had significantly higher T
concentrations then the Far bucks (P<.05). Females significantly preferred the Near buckscented rags (P<.001). Taken together, these studies suggest that chemical cues provided
by urine and sebaceous glands of male goats may be T-dependent. Females can use
91
chemical cues to distinguish among males with higher T concentrations, and are
potentially higher quality.
92
INTRODUCTION
Chemical cues may play an important role in female mate choice in mammals.
Functioning similarly to the conspicuous colors and ornamentation displayed by male
birds and fish (Ardia et al., 2010; Baldwin and Johnsen, 2009; Knapp and Kovach, 1991),
chemical cues can provide information about a male’s quality (Penn and Potts, 1998). For
several rodent species, chemical cues have been directly associated with a male’s
reproductive state (Carr et al., 1965), status (Gosling, 1990; Gosling and McKay, 1990;
Gosling et al., 2000), health (Kavaliers and Colwell, 1993), and genes (Eggert et al.,
1996; Ilmonen et al., 2009). Thus, chemical cues are likely difficult for a male to fake,
and may serve as an honest indicator that a female may use to assess a male.
Testosterone (T) often plays a key role in regulating male-typical reproductive
behaviors including scent marking and chemical constituents within (Bronson and
Whitten, 1968; Ferkin and Johnston, 1993; Ferkin et al., 1994; Hau, 2007; Johnston,
1981; Yahr et al., 1979). High T concentrations impose energetic costs (Buchanan et al.,
2001; Wingfield et al., 2001) and immune suppression (Marsh, 1992; Marsh and Scanes,
1994) to male birds; preventing a male from falsely advertising his fitness status. Folstad
and Karter (1992) proposed that a negative feedback loop exists between expression of Tdependent secondary sexual characteristics and parasite load. Accordingly, T-dependent
secondary sexual characteristics are reliable indicators of heritable parasite resistance;
preventing a male from falsely advertising his quality. Testosterone concentration may be
an honest indicator of a male’s quality and resulting T-dependent behaviors such as scent
marking and associated chemical cues may be used as a cue to assess male quality.
93
Using chemical cues alone, females are able to distinguish between and show
preference for particular males. Female rodents prefer odors from dominant males
(Drickamer, 1992; Mossman and Drickamer, 1996), less parasitized males (Penn and
Potts, 1998), and non-related males (Brennan, 2004; Brown et al., 1987; Roberts, 2009;
Schwensow et al., 2008; Singh et al., 1987; Spehr et al., 2006). Studies have also shown
that chemical cues provided by the male may stimulate physiological changes in females.
Chemical cues may act as primer pheromones, accelerating puberty in rodents (Colby and
Vandenberg, 1974; Kaneko et al., 1980; MacIntosh Schellinck et al., 1993) or increasing
ovulation frequencies in ungulates (Bowyer et al., 1994; Coblentz, 1976; Gelez et al.,
2004a; Gelez and Fabre-Nys, 2006; Miquelle, 1991; Preti et al., 2003; Walkden-Brown et
al., 1993). A female’s physiological response to chemical cues provided by a male is
stereotypical as suggested by studies on the “male effect.” The “male effect” is a well
described phenomenon whereby presentation of ram or buck odor to anestrous females
prior to the onset of the breeding season causes an immediate increase in luteinizing
hormone, and eventual ovulation (Chemineau, 1983; Martin et al., 1980; Oldham et al.,
1979; Signoret, 1991; Walkden-Brown et al., 1993). This unique phenomenon suggests
that male chemical cues may be critically important to reproduction for females.
Much of current understanding of the role scent marking and chemical cues in
mammalian mate choice has come from studies using laboratory rodents. However, scent
marking has been well described in male ungulates. Male ungulates scent mark the
ground, surrounding areas or themselves with glandular secretions and urine, distributing
chemical cues (Walther, 1984). Ungulates have multiple active scent glands on different
parts of the body (Gosling, 1985; Jenkinson et al., 1967). In addition to or enhancing
94
chemical cues provided by scent glands, males often scent mark themselves. This scent
marking behavior is referred to as scent-urination (Coblentz, 1976) or self-enurination
(Price et al., 1986). Males impregnate their hair with urine either by urinating directly
onto themselves or by wallowing in urine pits (reviewed in: Coblentz, 1976; Walther,
1984). It was initially believed that scent marking was used predominantly for territorial
demarcation (Owen-Smith, 1977) as many ungulates often scent mark along territory
boarders (reviewed in: Walther, 1984). However, scent marking was also observed in
several non-territorial species suggesting that chemical cues provided by males may serve
additional purposes (Johnson, 1973; Ralls, 1971); possibly for mate choice.
Previous studies from our laboratory indicate that estrous does prefer intact males
compared to females (Margiasso et al., 2010) and prefer males with higher T
concentrations (Longpre and Katz, In Press), however it is not clear how females made
these distinctions. It is possible that the same chemical cues provided by the male to
induce the “male effect” may also be used by the female for mate choice. In this study, it
is predicted that female’s will show preference for male chemical cues from males with
higher T concentrations.
95
MATERIALS AND METHODS
Animals
All animals were Alpine goats between the ages of 2-10 years which received a
diet consisting of grass hay and grain, and had ad libitum access to water and mineral salt
blocks. Diet and husbandry was in compliance with the Consortium Guide for the Care
and Use of Agricultural Animals in Agricultural Research and Education (FASS, 2010).
Research was conducted as approved by the Rutgers University Animal Care and
Facilities Committee. Male and female goats were housed on the NJ Agricultural
Experiment Station Research Farm in New Brunswick, NJ (40° 29' 10" N / 74° 27' 8" W)
in barns with free access to outdoor exercise areas. The breeding season for the Alpine
goat begins in mid-August and terminates near the end of January in the northern
hemisphere. Focal goats were estrous-synchronized females. Scent impregnated cloth
rags used in the preference tests were rubbed on males in various reproductive states.
Bucks (n=10) are gonadally intact males and wethers (n=13) are males castrated prepubertally.
Estrus Synchronization and Detection
Focal goats were estrous-synchronized females drawn from a herd of 24. The herd
was divided into two groups which were estrous-synchronized on alternating weeks.
Estrous synchronization was accomplished using a sequential treatment with
prostaglandin (PGF 2α ). During the breeding season, mid-August through January, each
female received two injections of 10 mg PGF 2α (i.m.) at 13 days prior and 51 hours prior
to the behavior test (Ott et al., 1980). For experiments conducted as females entered the
96
non-breeding season, estrus was either synchronized using the protocol above or induced
by providing supplementary progestins and estradiol (Billings and Katz, 1997; 1999).
Standing estrus was detected prior to each behavior test. A non-experimental
buck was brought into the females’ home pen and allowed to mount females but not
allowed to intromit. If the female stood to be mounted, she was considered to be in estrus.
If the female rejected the male, she was considered non-estrous. All females, regardless
of estrous state, were tested in the behavior experiment; however, only data from estrous
females are reported.
Scented Rags
Rags used for preference tests were 100% cotton and rubbed on each of the
respective males every day beginning 2 weeks prior to the behavior test by research
students wearing VWR® Microgryp® Purple Nitrile® gloves. For each experiment, rags
were rubbed on males housed in a large group; Experiment 1: bucks, wethers and
Experiment 2: Near bucks, Far bucks. See Partner preference testing: Experiment 2
section below for definitions of Near and Far bucks. Each rag rubbing session was
approximately 15 m in duration. Rags were rubbed vigorously by pressing the cloth on
the males face, beard, and neck regions. Between each rag rubbing session, rags were
stored individually in large gallon size Ziploc® bags. Each bag was then placed
individually inside a plastic Sterilite® container within each barn. Control rags were
stored in a large Ziploc® bag and placed in a container within the laboratory.
Blood Sampling and Radioimmunoassay (RIA)
97
Blood samples were collected from bucks during both studies on a weekly basis
and from wethers on a monthly basis at 0800hrs via jugular venipuncture during the
breeding season. Serum was stored at -20 °C until assayed.
Serum testosterone concentrations were determined by commercial RIA kit
(Beckman Coulter DSL-4000, Webster, Tx), and validated in our lab for goat serum. For
experiment 1, the minimum detection limit of the DSL-4000 assay was 0.01 ng/ml and
the inter-assay coefficient of variation was 11%. For experiment 2, the minimum
detection limit of the DSL-4000 assay was 0.02 ng/ml and the inter-assay coefficient of
variation was 12%.
Statistical Analysis
Preference Tests: For each of the two trials the female’s preference for a particular male
(e.g. buck-scented rag versus control rag) was computed by calculating a preference score
as follows:
In Experiment 1, for each female the two preference scores for a particular male were
averaged. In Experiment 2, there was only one trial. A female’s preference for a
particular male was calculated using the same formula as above. Preference scores were
determined to be different from chance (50%) using a binomial test. Variation in
preference scores is reported as standard error of the proportion (± SEP). Results were
deemed significant at P<0.05 (NCSS Statistical Software, 2001, Kaysville, UT).
Blood Samples:
98
Differences in serum T concentrations between bucks and wethers, and Near and
Far bucks were compared using a t test for independent samples. Results were deemed
significant at P<0.05 (NCSS Statistical Software, 2001, Kaysville, UT).
Experiment 1
To determine if females use olfactory cues to distinguish among males in different
reproductive states, specifically with different T concentrations, females were given a
choice between buck scented and control rags and buck-scented and wether-scented rags.
Partner Preference Testing
Females were acclimated to the test apparatus (Fig. 1) for two weeks prior to the
behavior test. Trials commenced once all females showed no signs of stress (e.g.,
vocalizing, jumping) while in the test apparatus.
Minutes prior to the start of each behavior test, scented rags were cut into 1 inch
strips and affixed to the front panel of the pen facing the incentive zone. Goats are very
social animals and often become stressed when alone in the test apparatus. Wethers
(castrated pre-pubertally) were placed within the holding pens at both ends of the test
apparatus and remained there for the duration of the trial to reduce the stress of the
female goats when in the test apparatus. The following choices were tested: Buck-scented
vs. control-scented rags scented rags and Buck-scented vs. wether-scented rags. For each
preference test 20 estrous females were tested.
To account for any side biases, a switchback design was used. Accordingly,
female subjects were placed in the test apparatus for two trials. During each trial, the
female was led to the center of the neutral zone and released. She was allowed to travel
the test apparatus for 5 min. Use of a 5-min trial period was determined after observation
99
of estrous females within the test apparatus. Preference trials lasting longer than 5 min
resulted in females becoming agitated. Further, for all experiments conducted, females
visited both sides of the apparatus within the allotted time. Total time spent in the
incentive zone near each male was recorded for each trial. For the switch back, males
were removed from the holding pen on one end of the test apparatus and placed in the
holding pen on the opposite end of the test apparatus. Females were then re-tested using
the same protocol as above.
Experiment 2:
To determine if T concentrations could be altered in a herd of bucks by housing
them with visual contact to females or with no visual contact and, in turn, if females
could distinguish between and show preference for odor cues from bucks housed under
these two different conditions.
Housing
Beginning on August 4, prior to the onset of the breeding season, bucks were
randomly assigned to live in one of two housing conditions. One group of bucks were
housed with fence-line contact and visual with females (Near bucks, n=5). Females
housed next to males were estrus synchronized throughout the study. The other herd of
bucks were housed with no visual and no fence-line contact to females (Far bucks, n=5).
After 10 wks, the Far bucks were moved to live with the Near bucks so all bucks had
fence-line contact with females. All males remained living together, with fence-line
contact to females for the remainder of the breeding season.
Partner Preference Testing
100
Prior to the start of Experiment 2, a new test apparatus and preference test
protocol was developed. All focal females were acclimated to the test apparatus for two
weeks (Fig. 2) prior to the behavior test. Trials commenced once all subject females
showed no signs of stress (vocalizing, jumping, etc.) while in the test apparatus.
Similar to experiment 1, scented rags that were rubbed on the Near and Far bucks
during the first 10 wks of the study while they were housed separately, were cut into 1
inch strips and affixed to the front panel of the pen facing the incentive zone prior to the
start of the behavior test. Two ovariectomized (OVX) females, similar morphology to
wethers, were placed within each of the holding pens at both ends of the test apparatus
and remained there for the duration of the trial. Placement of OVX females inside the
goal pen was to reduce the stress of the female goats when in the test apparatus.
Placement of each panel on either side of the apparatus varied for each focal female goat
and was randomized. When panels were moved from one side of the apparatus to the
opposite side of the apparatus, OVX females remained within the holding pens that they
were originally placed in. The front panel containing the scented rags was removed from
the holding pen on one end of the test apparatus and attached to the holding pen on the
opposite end of the test apparatus.
A total of 11 estrous females were placed within the test apparatus for one trial.
During each trial, one estrous female subject was led to the center of the neutral zone and
released. She was allowed to travel the test apparatus for 5 min. Use of a 5-min trial
period was determined after observation of estrous females within the test apparatus.
Preference trials lasting longer than 5 min resulted in females becoming agitated. Total
time spent in the incentive zone near each male was recorded for each trial.
101
RESULTS
Experiment 1
When estrous females were given a choice between plain rags and buck-scented
rags, females spent a greater amount of time in the buck-scented rag incentive zone (IZ)
compared to the plain rag IZ (P<0.001; Figure 3). Further, estrous females were given a
choice between buck-scented and wether-scented rags, estrous females spent a greater
amount of time in the buck-scented rag IZ compared to the plain rag IZ (P<0.001; Figure
3). Bucks have higher T concentrations then wethers (P<0.001; Figure 4).
Experiment 2
When females were given a choice between two intact males, estrous females
spent a greater amount of time in the Near buck-scented rags IZ compared to the Far
buck-scented rags IZ (P<0.001; Figure 5). The Near bucks had higher T concentrations at
the time during which rags were rubbed on them (P<.05; Figure 6).
102
DISCUSSION
Estrous female goats displayed a clear preference for olfactory cues from bucks,
specifically bucks with higher serum T concentrations. This is the first study to
demonstrate the estrous female goats are attracted to and prefer chemical cues from intact
males. Females preferred chemical cues on the buck-scented rags over the control rag.
This result is consistent with observations in other species. Female pigs spent more time
in close proximity to intact versus castrated males regardless if they were active or
anesthetized (Signoret, 1976), suggesting that chemical cues from intact males may
attract females. Female ewes have been described as seeking out rams when in estrous,
perhaps using chemical cues to locate them (Banks, 1964; Lindsay, 1966). Anosmia
results in a decreased ovulatory response displayed by female ewes and a decreased
detection of or attraction to ram chemical cues (Gelez et al., 2004b; Gelez and Fabre-Nys,
2004), further suggesting that male chemical cues, rather than the presence of the males,
are important to females.
Estrous females demonstrated a clear preference for chemical cues from males
with higher T concentrations. Differences in T concentrations between the bucks and
wethers (Experiment 1), and Near and Far bucks (Experiment 2) likely resulted in
differences in chemical cues provided on the scented rags. Scented rags contained both
urinary and sebaceous gland chemical cues. Iwata et al. (2000) and Iwata et al. (2001)
found that male goat sebaceous gland size and pheromone activity are T-dependent. The
domesticated goat has undergone strong artificial selection pressures, however such
domestication pressures have not overcome the strength of sexual selection as sexually
selected characteristics including chemical cues are robust. Chemical characteristics of
103
male urine were also found to vary depending on T concentrations for moose (Achiraman
and Archunan, 2005; Whittle et al., 2000b), elephants (Poole et al., 1984; Rasmussen and
Schulte, 1998; Schulte et al., 2007), zebra (Chaudhuri and Ginsberg, 1990), a variety of
deer (Miller et al., 1998; Monfort et al., 1995) and llamas (Paul Murphy et al., 1991).
Chemical cues within buck urine may also vary with T concentrations. Similarly to
chemical cues of non-domesticated ungulates, bucks with higher T concentrations may
have urine with different chemical characteristics then males with lower T
concentrations. Females could use differences detected in urine to distinguish among
males with high T and low T concentrations.
In the wild, estrous female elephants (Rasmussen and Schulte, 1998), moose
(Bowyer et al., 1994; Bowyer et al., 1998; Whittle et al., 2000a) and bison (Bowyer et al.,
1998) are also attracted to chemical cues distributed by males. Attraction to male
chemical cues may be energetically advantageous to females. Females often live in
unisex groups, only interacting with males during the breeding season (Alexander et al.,
1980; Walkden-Brown et al., 1999). Females attraction to and ability to locate males
using olfactory cues alone likely decreases energetic costs (Marler and Moore, 1989;
Rose, 1981) and predation risks (Lister and Aguayo, 1992; Yoder et al., 2004) that may
be associated with searching for males. Further, males with higher T concentrations are
higher quality as they are usually more dominant and aggressive (Albert et al., 1990;
Cavigelli and Pereira, 2000; Marler and Moore, 1988; Marler and Moore, 1989;
McGlothlin et al., 2008; Wingfield et al., 1987) and are in better health (Folstad and
Karter, 1992; Penn and Potts, 1998). Females may gain indirect benefits by mating with
high quality males as their offspring will benefit from their sire’s good genes.
104
In summary, female goats prefer chemical cues from males with higher T
concentrations over those with lower T concentrations. Males with high T concentrations
are likely higher quality; hence, chemical cues from high quality males may be more
attractive and are preferred by females. Chemical cues from high quality males may
stimulate female reproductive physiology and behavior including ovulation, seeking
behavior, and preference, increasing the likelihood that females will mate exclusively
with high quality mates.
105
Figure 1
Figure 1. Test apparatus for buck vs wether-scented and control rag female
preference test paradigm: The apparatus was divided in the middle by a 2.4 m neutral
zone. The neutral zone was defined by two 2.4 m wide pieces of shade cloth that reached
floor to ceiling and were against opposite walls such that the openings to the incentive
zones were staggered. Each incentive zone contained a 1.5 m x 3 m holding pen. Malescented rags were tied to the front panel of each pen facing the incentive zone.
106
Figure 2
Figure 2. Test apparatus for “Near” and “Far” buck-scented rag female preference
test paradigm: The apparatus was divided in the middle by a 11.6m neutral zone. The
neutral zone was defined by chalk lines on the floor that ran up the wall on each side of
the test apparatus. Each incentive zone contained a 1.5m x 3m holding pen.
107
Figure 3
Figure 3. Estrous females prefer buck-scented rags: Mean (±SEP) preference scores
for buck-scented and control rags. Number of estrus females used for each preference test
was 20. * Denotes significant difference (P<0.001).
108
Figure 4
Mean Serum T Concentrations (ng/ml)
16
14
*
12
10
8
6
4
2
0
Bucks
Wethers
Figure 4. Serum T concentrations for bucks and wethers: Mean (± SEM) serum T
concentrations for bucks (n=6) and wethers (n=10) during October and November of the
breeding season when rags were rubbed on each respective group of males. * Denotes
significant difference (P<0.001).
109
Figure 5
100
Preference Score (%)
80
*
60
40
20
0
Near Buck-scented
Far Buck-scented
Rag Type
Figure 5. Estrous females prefer Near buck-scented rags: Mean (±SEP) preference
scores for Near buck-scented and Far buck-scented rags. Number of estrus females used
was 11. * Denotes significant difference (P<0.001).
110
Figure 6
Mean Serum T Concentrations (ug wk ml-1)
1200
*
1000
800
600
400
200
0
Near Bucks
(n=5)
Far Bucks
(n=5)
Figure 6. Serum T concentrations for Near and Far bucks: Mean (± SEM) serum T
concentrations for Near bucks (n=5) and Far bucks (n=5) during the breeding season. T
concentrations are represented as area under the curve for weekly collections (August 3
to October 12). * Denotes significant difference (P<0.05).
111
REFERENCES
Achiraman, S., and Archunan, G., 2005. 3-Ethyl-2, 7-dimethyl octane, a testosterone
dependent unique urinary sex pheromone in male mouse (Mus musculus). An
Reprod Sci. 87, 151-161.
Albert, D. J., Jonik, R. H., Watson, N. V., Gorzalka, B. B., and Walsh, M. L., 1990.
Hormone-dependent aggression in male rats is proportional to serum testosterone
concentration but sexual behavior is not. Physiol Behav. 48, 409-16.
Alexander, G., Signoret, J. P., and Hafez, E. S. E., 1980. Sexual, maternal and neonatal
behavior. In: Hafez, E.S.E. (ed). Reproduction Farm Anim. pp 304-334. Lea &
Febiger, Philadelphia, PA.
Ardia, D. R., Broughton, D. R., and Gleicher, M. J., 2010. Short-term exposure to
testosterone propionate leads to rapid bill color and dominance changes in zebra
finches. Horm Behav. 58, 526-532.
Baldwin, J., and Johnsen, S., 2009. The importance of color in mate choice of the blue
crab Callinectes sapidus. J Exp Biol. 212, 3762.
Banks, E. M., 1964. Some aspects of sexual behavior in domestic sheep, Ovis aries.
Behaviour. 249-279.
Billings, H. J., and Katz, L. S., 1997. Progesterone Facilitation and Inhibition of
Estradiol-Induced Sexual Behavior in the Female Goat. Horm Behav. 31, 47-53.
Billings, H. J., and Katz, L. S., 1999. Facilitation of sexual behavior in French-Alpine
goats treated with intravaginal progesterone-releasing devices and estradiol during
the breeding and nonbreeding seasons. J Anim Sci. 77, 2073-8.
Bowyer, R. T., Manteca, X., and Hoymork, A. 1998. Scent marking in American bison:
morphological and spatial characteristics of wallows and rubbed trees, pp. 81-91.
In L. R. Irby and J.E. Knight (eds.). International Symposium on Bison Ecology in
North America. Bozeman, Montana.
Brennan, P. A., 2004. The nose knows who's who: chemosensory individuality and mate
recognition in mice. Horm Behav. 46, 231-40.
Bronson, F. H., and Whitten, W. K., 1968. Oestrus-accelerating pheromone of mice:
assay, androgen-dependency and presence in bladder urine. Reproduction. 15,
131.
Brown, R. E., Singh, P. B., and Roser, B., 1987. The major histocompatibility complex
and the chemosensory recognition of individuality in rats. Physiol Behav. 40, 6573.
Buchanan, K. L., Evans, M. R., Goldsmith, A. R., Byrant, D. M., and Rowe, L. V., 2001.
Testosterone influences basal metabolic rate in male house sparrows: a new cost
of dominance signaling? Proc Roy Soc B. 268, 1337-1344.
Carr, W. J., Loeb, L. S., and Dissinger, M. L., 1965. Responses of Rats to Sex Odors. J
Comp Physiol Psychol. 59, 370-7.
Cavigelli, S. A., and Pereira, M. E., 2000. Mating season aggression and fecal
testosterone levels in male ring-tailed lemurs (Lemur catta). Horm Behav. 37,
246-55.
Chaudhuri, M., and Ginsberg, J. R., 1990. Urinary androgen concentrations and social
status in two species of free ranging zebra (Equus burchelli and E. grevyi).
Reproduction. 88, 127.
112
Chemineau, P., 1983. Effect on oestrus and ovulation of exposing creole goats to the
male at three times of the year. J Reprod Fertil. 67, 65-72.
Coblentz, B. E., 1976. Functions of scent-urination in ungulates with special reference to
feral goats (Capra hircus L.). Am Nat. 110, 549-557.
Colby, D. R., and Vandenberg, J. G., 1974. Regulatory effects of urinary pheromones on
puberty in the mouse. Biol Reprod. 11, 268.
Drickamer, L. C., 1992. Oestrous female house mice discriminate dominant from
subordinate males and sons of dominant from sons of subordinate males by odour
cues. Anim Behav. 43, 868-870.
Eggert, F., Höller, C., Luszyk, D., Müller-Ruchholtz, W., and Ferstl, R., 1996. MHCassociated and MHC-independent urinary chemosignals in mice. Physiol Behav.
59, 57-62.
FASS, 2010. Guide for the care and use of agricultural animals in research and
teaching, 3rd ed. Fed. Anim. Sci. Soc., Champagne, IL.
Ferkin, M. H., and Johnston, R. E., 1993. Roles of gonadal hormones in control of five
sexually attractive odors of meadow voles (Microtus pennsylvanicus). Horm
Behav. 27, 523-538.
Ferkin, M. H., Sorokin, E. S., Renfroe, M. W., and Johnston, R. E., 1994. Attractiveness
of male odors to females varies directly with plasma testosterone concentration in
meadow voles. Physiol Behav. 55, 347-353.
Folstad, I., and Karter, A. J., 1992. Parasites, bright males, and the immunocompetence
handicap. Am Nat. 139, 603.
Gelez, H., Archer, E., Chesneau, D., Campan, R., and Fabre-Nys, C., 2004a. Importance
of learning in the response of ewes to male odor. Chem Senses. 29, 555-63.
Gelez, H., Archer, E., Chesneau, D., Magallon, T., and Fabre-Nys, C., 2004b.
Inactivation of the olfactory amygdala prevents the endocrine response to male
odour in anoestrus ewes. Eur J Neurosci. 19, 1581-90.
Gelez, H., and Fabre-Nys, C., 2004. The "male effect" in sheep and goats: A review of
the respective roles of the two olfactory systems. Horm Behav. 46, 257-271.
Gelez, H., and Fabre-Nys, C., 2006. Role of the olfactory systems and importance of
learning in the ewes' response to rams or their odors. Reprod Nutr Dev. 46, 40115.
Gosling, L. M., 1985. The even-toed ungulates: order Artiodactyla. In Brown, E. D. and
MacDonald, D. (ed). Social odours in mammals. pp. 550–618. Oxford: Oxford
University Press.
Gosling, L. M., 1990. Scent marking by resource holders: alternative mechanisms for
advertising the costs of competition. In MacDonald, D., Muller-Schwarze, and
Natnyczuk, S.E. (ed). Chemical Signals in Vertebrates, vol. 5. pp. 315–328.
Oxford: Oxford University Press.
Gosling, L. M., and McKay, H. V., 1990. Scent-rubbing and status signaling by male
mammals. Chem Ecol. 1, 92-95.
Gosling, L. M., Roberts, S. C., Thornton, E. A., and Andrew, M. J., 2000. Life history
costs of olfactory status signaling in mice. Behav Ecol Sociobiol. 48, 328-332.
Hau, M., 2007. Regulation of male traits by testosterone: implications for the evolution of
vertebrate life histories. BioEssays. 29, 133-144.
113
Ilmonen, P., Stundner, G., Thoss, M., and Penn, D. J., 2009. Females prefer the scent of
outbred males: good-genes-as-heterozygosity? BMC Evol Biol. 9, 104.
Iwata, E., Wakabayashi, Y., Kakuma, Y., Kikusui, T., Takeuchi, Y., and Mori, Y., 2000.
Testosterone-dependent primer pheromone production in the sebaceous gland of
male goat. Biol Reprod. 62, 806-810.
Iwata, E., Wakabayashi, Y., Matsuse, S., Kikusui, T., Takeuchi, Y., and Mori, Y., 2001.
Induction of primer pheromone production by dihydrogentestosterone in the male
goat. J Vet Med Sci. 63, 347-348.
Jenkinson, D. M., Blackburn, P. S., and Proudfoot, R., 1967. Seasonal changes in the skin
glands of the goat. Br Vet J. 123, 541-9.
Johnson, R. P., 1973. Scent marking in mammals. Anim Behav. 21, 521-535.
Johnston, R. E., 1981. Testosterone dependence of scent marking by male hamsters
(Mesocricetus auratus). Behav Neural Biol. 31, 96-99.
Kaneko, N., Debski, E. A., Wilson, M. C., and Whitten, W. K., 1980. Puberty
acceleration in mice. II. Evidence that the vomeronasal organ is a receptor for the
primer pheromone in male mouse urine. Biol Reprod. 22, 873.
Kavaliers, M., and Colwell, D. D., 1993. Aversive responses of female mice to the odors
of parasitized males: neuromodulatory mechanisms and implications for mate
choice. Ethology. 95, 202-212.
Ketterson, E. D., Nolan, V., Jr., Wolf, L., Ziegenfus, C., Dufty, A. M., Jr., Ball, G. F.,
and Johnsen, T. S., 1991. Testosterone and avian life histories: the effect of
experimentally elevated testosterone on corticosterone and body mass in darkeyed juncos. Horm Behav. 25, 489-503.
Knapp, R. A., and Kovach, J. T., 1991. Courtship as an honest indicator of male parental
quality in the bicolor damselfish, Stegastes partitus. Behav Ecol. 2, 295.
Lindsay, D. R., 1966. Mating behaviour of ewes and its effect on mating efficiency.
Anim Behav. 14, 419-424.
Lister, B. C., and Aguayo, A. G., 1992. Seasonality, predation, and the behaviour of a
tropical mainland anole. J Anim Ecol. 61, 717-733.
Longpre, K. M., and Katz, L. S., In Press. Estrous female goats use testosteronedependent cues to assess mates. Horm Behav.
MacIntosh Schellinck, H., Smyth, C., Brown, R., and Wilkinson, M., 1993. Odor-induced
sexual maturation and expression of c-fos in the olfactory system of juvenile
female mice. Dev Brain Res. 74, 138-141.
Margiasso, M. E., Longpre, K. M., and Katz, L. S., 2010. Partner preference: Assessing
the role of the female goat. Physiol Behav. 99, 587-591.
Marler, C. A., and Moore, M. C., 1988. Evolutionary costs of aggression revealed by
testosterone manipulations in free-living male lizards. Behav Ecol Sociobiol. 23,
21-26.
Marler, C. A., and Moore, M. C., 1989. Time and energy costs of aggression in
testosterone-implanted free-living male mountain spiny lizards (Sceloporus
jarrovi). Physiol Zool. 62, 1334-1350.
Martin, G. B., Oldham, C. M., and Lindsay, D. R., 1980. Increased plasma LH levels in
seasonally anovular Merino ewes following the introduction of rams. Anim
Reprod Sci. 3, 125-132.
114
McGlothlin, J. W., Jawor, J. M., Greives, T. J., Casto, J. M., Phillips, J. L., and Ketterson,
E. D., 2008. Hormones and honest signals: males with larger ornaments elevate
testosterone more when challenged. J Evol Biol. 21, 39-48.
Miller, K. V., Jemiolo, B., Gassett, J. W., Jelinek, I., Wiesler, D., and Novotny, M., 1998.
Putative chemical signals from white-tailed deer (Odocoileus virginianus): social
and seasonal effects on urinary volatile excretion in males. J Chem Ecol. 24, 673683.
Miquelle, D. G., 1991. Are moose mice? The function of scent urination in moose. Am
Nat. 138, 460-477.
Monfort, S. L., Harvey, E., Geurts, L., Padilla, L., Simmons, H. A., Williamson, L. R.,
and Wildt, D. E., 1995. Urinary 3 alpha, 17 beta-androstanediol glucuronide is a
measure of androgenic status in Eld's deer stags (Cervus eldi thamin). Biol
Reprod. 53, 700.
Mossman, C. A., and Drickamer, L. C., 1996. Odor preferences of female house mice
(Mus domesticus) in seminatural enclosures. J Comp Psychol. 110, 131-138.
Oldham, C. M., Martin, G. B., and Knight, T. W., 1979. Stimulation of seasonally
anovular Merino ewes by rams. I. Time from introduction of the rams to the
preovulatory LH surge and ovulation. Anim Reprod Sci. 1, 283-290.
Ott, R. S., Nelson, D. R., and Hixon, J. E., 1980. Fertility of goats following
synchronization of estrus with prostagland in F2[alpha]. Theriogenology. 13, 341345.
Owen-Smith, N., 1977. On territoriality in ungulates and an evolutionary model. Q Rev
Biol. 52, 1-38.
Paul Murphy, J., Tell, L. A., Bravo, W., Fowler, M. E., and Lasley, B. L., 1991. Urinary
steroid evaluations to monitor ovarian function in exotic ungulates: VIII.
Correspondence of urinary and plasma steroids in the llama (Lama glama) during
nonconceptive and conceptive cycles. Zoo Biol. 10, 225-236.
Penn, D., and Potts, W. K., 1998. Chemical signals and parasite-mediated sexual
selection. Trends Ecol Evol. 13, 391-396.
Poole, J. H., Kasman, L. H., Ramsay, E. C., and Lasley, B. L., 1984. Musth and urinary
testosterone concentrations in the African elephant (Loxodonta africana). J
Reprod Fertil. 70, 255-60.
Preti, G., Wysocki, C. J., Barnhart, K. T., Sondheimer, S. J., and Leyden, J. J., 2003.
Male axillary extracts contain pheromones that affect pulsatile secretion of
luteinizing hormone and mood in women recipients. Biol Reprod. 68, 2107.
Price, E. O., Smith, V. M., and Katz, L. S., 1986. Stimulus conditions influencing selfenurination, genital grooming and flehmen in male goats. Appl Anim Behav Sci.
16, 371-381.
Ralls, K., 1971. Mammalian scent marking. Science. 171, 443-9.
Rasmussen, L. E., and Schulte, B. A., 1998. Chemical signals in the reproduction of
Asian (Elephas maximus) and African (Loxodonta africana) elephants. Anim
Reprod Sci. 53, 19-34.
Roberts, S. C., 2009. Complexity and context of MHC-correlated mating preferences in
wild populations. Mol Ecol. 18, 3121-3.
Rose, B., 1981. Factors affecting activity in Sceloporus virgatus. Ecology. 62, 706-716.
115
Schulte, B. A., Freeman, E. W., Goodwin, T. E., Hollister-Smith, J., and Rasmussen, L.,
2007. Honest signalling through chemicals by elephants with applications for care
and conservation. Appl Anim Behav Sci. 102, 344-363.
Schwensow, N., Eberle, M., and Sommer, S., 2008. Compatibility counts: MHCassociated mate choice in a wild promiscuous primate. Proc Biol Sci. 275, 555-64.
Setchell, J. M., Charpentier, M. J. E., Abbott, K. M., Wickings, E. J., and Knapp, L. A.,
2010. Opposites attract: MHC-associated mate choice in a polygynous primate. J
Evol Biol. 23, 136-148.
Signoret, J. P., 1976. Chemical communication and reproduction in domestic mammals.
In Doty, R. L. (ed). Mammalian olfaction, reproductive processes and behavior.
pp. 243-256. Academic Press, New York, NY.
Signoret, J. P., 1991. Sexual pheromones in the domestic sheep: importance and limits in
the regulation of reproductive physiology. J Steroid Biochem Mol Biol. 39, 63945.
Singh, P. B., Brown, R. E., and Roser, B., 1987. MHC antigens in urine as olfactory
recognition cues. Nature. 327, 161-4.
Spehr, M., Kelliher, K. R., Li, X. H., Boehm, T., Leinders-Zufall, T., and Zufall, F.,
2006. Essential role of the main olfactory system in social recognition of major
histocompatibility complex peptide ligands. J Neurosci. 26, 1961-70.
Walkden-Brown, S. W., Martin, G. B., and Restall, B. J., 1999. Role of male-female
interaction in regulating reproduction in sheep and goats. J Reprod Fertil Suppl.
54, 243-57.
Walkden-Brown, S. W., Restall, B. J., and Henniawati, 1993. The male effect in the
Australian cashmere goat. 2. Role of olfactory cues from the male. Anim Reprod
Sci. 32, 55-67.
Walther, F. R., 1984. Communication and expression in hoofed mammals. Indiana Univ
Pr.
Whittle, C., Bowyer, R. T., Clausen, T. P., and Duffy, L. K., 2000a. Putative pheromones
in urine of rutting male moose (Alces alces): evolution of honest advertisement? J
Chem Ecol. 26, 2747-2762.
Whittle, C. L., Bowyer, R. T., Clausen, T. P., and Duffy, L. K., 2000b. Putative
pheromones in urine of rutting male moose (Alces alces): evolution of honest
advertisement? J Chem Ecol. 26, 2747-2762.
Wingfield, J. C., 1984. Androgens and mating systems: testosterone-induced polygyny in
normally monogamous birds. Auk. 101, 665-671.
Wingfield, J. C., Ball, G. F., Dufty Jr, A. M., Hegner, R. E., and Ramenofsky, M., 1987.
Testosterone and aggression in birds. Am Sci. 75, 602-608.
Yahr, P., Newman, A., and Stephen, D. R., 1979. Sexual behavior and scent marking in
male gerbils: Comparison of changes after castration and testosterone
replacement. Horm Behav. 13, 175-184.
Yoder, J. M., Marschall, E. A., and Swanson, D. A., 2004. The cost of dispersal:
predation as a function of movement and site familiarity in ruffed grouse. Behav
Ecol. 15, 469.
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CHAPTER V
THE COST OF MAINTAINING HIGH TESTOSTERONE
CONCENTRATIONS: IMPLICATIONS
FOR LIFE-HISTORY TRADE-OFFS
117
ABSTRACT
Sexual selection may have great influence on the life-history traits of males as
reproductive effort, including the increased expression of secondary sexual characteristics
and behaviors, improves a male’s reproductive success. Testosterone regulates the
expression of a large suite of male secondary sexual characteristics. Alteration in T
production depending on male quality and reproductive opportunities may provide males
with the ability to invest differentially in reproductive effort to minimize reproductive
costs. To test the effect of the presence of females on circulating testosterone (T)
concentrations, males were housed with both fence-line and visual contact with females
(Near bucks, n=5), or no fence-line nor visual contact with females (Far bucks, n=5),
beginning Aug 4, prior to the onset of the breeding season. After 10 wk, the Far bucks
were added to the Near so all had fence-line contact with females. Weekly blood samples
were collected for the duration of the experiment. Far bucks had significantly lower T
concentrations than Near for the first 10 wk (P<.05; 0.65 ± 0.3 vs. 1.2 ± 0.05 µg·wk/ml,
respectively). After fence-line contact with females, T concentrations for the Far bucks
increased and were similar to those of the Near bucks. Mean T concentrations for the two
blood samples prior to the move for Far and Near bucks were 8.0 ± 2.2 and 15.5 ± 0.7
ng/ml, respectively, and after the move were 12.6 ± 1.8 and 14.2 ± 0.7 ng/ml,
respectively. In addition, body weights were measure for bucks weekly and for TPtreated males every 3 months for one. For both the bucks and TP-treated males, body
mass loss was greatest when T concentrations were high. Taken together, these studies
suggest that T may serve as a physiological mechanism that mediates life-history tradeoffs for males.
118
Keywords: Testosterone, Life-history trade-offs, sexual selection
119
INTRODUCTION
Female mate choice is an evolutionary process whereby sexual selection pressures
have resulted in the display of extravagant male phenotypes that cannot be accounted for
by natural selection or male-male competition (Andersson, 1994; Darwin, 1871; Krebs
and Davies, 1978). Extravagant secondary sexual characteristics such as bright
coloration, intricate songs, ornate visual signals and chemical cues have all received
considerable attention in the study of sexual selection, as females often choose to mate
with individuals displaying such characteristics (Andersson, 1982; Gentner and Hulse,
2000; Gosling and Roberts, 2001; Waitt et al., 2003). Due to the differential cost of
reproduction in promiscuous species, it is expected that females should mate with higher
quality males, while males should mate with a greater number of females (Andersson,
1994; Clutton-Brock and Vincent, 1991; Trivers, 1972). Extravagant secondary sexual
characteristics may serve as an indicator of a male’s quality, with the cost of the
characteristic directly related to the reliability of the indicator (Zahavi, 1975; Zahavi,
1977). Thus, a male’s quality is directly related to the degree of elaboration displayed,
such that males who are higher quality display more extravagant secondary sexual
characteristics and achieve greater fitness than those who are lower quality. To ensure
exclusive mating with high quality males, females should distinguish among males using
cues that impose a high cost; too high for a low quality male to produce. Variation
between quality and expression of secondary sexual characteristics is likely to exist as
male’s make trade-offs between self-maintenance and reproduction (Bell, 1980; Stearns,
1989). As a result of the high cost of reproduction, specifically the expression of
120
extravagant secondary sexual characteristics, sexual selection may have great influence
on the life-history traits of males.
Testosterone (T)-mediated functions may serve as physiological mechanisms that
mediate life-history trade-offs for males (Hau, 2007; Ketterson et al., 1991; Wingfield et
al., 2001). Testosterone regulates the expression of a large suite of male secondary sexual
characteristics (reviewed in: Hau, 2007; Rhen and Crews, 2002) and is important for the
expression of reproductive behaviors including aggression (Albert et al., 1990; Cavigelli
and Pereira, 2000; Marler and Moore, 1988; Marler and Moore, 1989; McGlothlin et al.,
2008; Wingfield et al., 1987), courtship (Damassa et al., 1977; Fusani, 2008; Fusani et
al., 2007; Fusani and Hutchison, 2003; Wiley and Goldizen, 2003), and chemical
signaling (Arteaga et al., 2008; Jainudeen et al., 1972; Miller et al., 1987; Yahr and
Thiessen, 1972). By increasing reproductive effort via increased expression of secondary
sexual characteristics and behaviors, a male may improve his reproductive success.
Although high circulating T concentrations have been shown to increase reproductive
effort, high T concentrations have also been shown to simultaneously decrease survival in
birds (Dufty, 1989; Ketterson et al., 1996) and lizards (Marler and Moore, 1988). Studies
using birds and lizards have also shown that high T concentrations negatively affect a
male’s health by causing immune suppression (Belliure et al., 2004; Duffy et al., 2000;
Grossman, 1984; Marsh and Scanes, 1994; Mougeot et al., 2004; Peters, 2000), and
increasing energetic costs through increasing metabolic rate (Buchanan et al., 2001;
Ryser, 1989) and increasing the loss of fat reserves (Ketterson et al., 1991; Wingfield,
1984). The display of T-dependent secondary sexual characteristics and behaviors is
energetically costly and males engaging in such behaviors are unable to simultaneously
121
forage or hunt for food (Gaunt et al., 1996; Mainguy and Côté, 2008; Marler and Moore,
1989; Wolff, 1998), leading to decreased body weights. Further, males with higher T
concentrations also have increased susceptibility to predation (Redpath et al., 2006) and
parasites (Mougeot et al., 2005; Seivwright et al., 2005). The negative effects of T on
male health and even survival may serve as important regulators of life-history trade-offs.
Plasticity in T production may provide males with the ability to invest
differentially in reproductive effort to minimize costs in the absence or presence of
reproductive opportunities. Males may maintain a breeding baseline concentration of T at
which spermatogenesis and normal mating activity is supported, and in response to a
social signal such as potential mates or male-male interactions, secrete more T and elicit
an appropriate T-dependent behavioral response (modified from the “Challenge
Hypothesis;” Wingfield et al., 1990). D'Occhio and Brooks (1982) found that T-replaced
wethers (prepuberally castrated male rams) given 10 or 100 mg/day of testosterone
propionate (TP) elicited full mating behavior after 2 weeks of treatment. Wethers dosed
with 4-8 mg/day TP displayed full mating behavior after 8 weeks of treatment, which
suggests that an initial increase in T is necessary for an early, initial response but not
necessary for maintenance of a full display of mating behavior. Acute increases in T
above baseline concentrations have been measured in males briefly exposed to aggressive
males (Harding and Follett, 1979; Pinxten et al., 2003; Ramenofsky, 1984; Wingfield,
1985). It has also been established that the presence of females can causes transient
increases in T concentrations (Graham and Desjardins, 1980; Illius et al., 1976; Purvis
and Haynes, 1974; Walkden-Brown et al., 1999). These studies suggest that T production
122
or secretion is minimized when social signals are low, in turn, minimizing the Tassociated risks when it is unnecessary.
In the presence of reproductive opportunities, T concentrations can increase and
males can respond accordingly. In the continuous presence of reproductive opportunities,
males may maintain elevated T concentrations, delaying termination of reproductive
activity and effort. Moore (1983) and Runfeldt and Wingfield (1985) found that male
white-crowned and song sparrows paired with females in a state of constant sexual
receptivity via estradiol treatments, maintained high circulating T concentrations longer
than males mated with control females. Males modify reproductive effort expressed in
response to female quality. Kelso and Verrell (2002) found that male veiled chameleons
adjust their courtship display in response to the female’s responsiveness. By decreasing
their reproductive effort, and presumably lowering T concentrations, in the presence of
low quality or less receptive females, males lower reproductive costs (Patricelli et al.,
2002; Runfeldt and Wingfield, 1985). By decreasing reproductive effort via a decrease in
T concentrations, males could avoid the risks and costs incurred when T concentrations
are high.
Little is known about the correlation between T concentrations and reproductive
effort in large mammals. It has been established that for a majority of seasonally breeding
species T concentrations increase and reach maximal concentrations early in the breeding
season and decrease thereafter (Busso, et al., 2005; Delgadillo, et al., 2004). Further,
studies also suggest that reproductive efforts are high during the breeding season, with
some males losing a significant amount of their body mass (Deutsch et al., 1990;
Galimberti et al., 2007; Leader-Williams and Ricketts, 1982; McElligott et al., 2003;
123
Miquelle, 1990). Using the domesticated goat as a model, the objectives of this study
were to determine if intact males invest differentially in reproduction by increasing or
decreasing T concentrations depending on reproductive opportunities available
(Experiment 1). It is predicted that the presence of females will cause an increase T
concentrations. In Experiment 2, we examined the costs of maintaining high T
concentrations by measuring body mass loss for both intact and T replaced males during
the breeding season. It is predicted the males with higher T concentrations will have
increased weight loss compared to those with lower T concentrations.
124
MATERIALS AND METHODS
Animals
All animals were Alpine goats between the ages of 2-5 years which received a
diet consisting of grass hay and grain, and had ad libitum access to water and mineral salt
blocks. Diet and husbandry was in compliance with the Consortium Guide for the Care
and Use of Agricultural Animals in Agricultural Research and Education (FASS, 2010).
Research was conducted as approved by the Rutgers University Animal Care and
Facilities Committee. Male and female goats were housed on the NJ Agricultural
Experiment Station Research Farm in New Brunswick, NJ (40° 29' 10" N / 74° 27' 8" W)
in barns with free access to outdoor exercise areas. The breeding season for the Alpine
goat begins in mid-August and terminates near the end of January in the northern
hemisphere. Males used were in various reproductive states. Bucks are gonadally intact
males and wethers are males castrated prepubertally. All females used were estrussynchronized.
Estrus Synchronization and Detection
Females were divided into two groups which were estrus-synchronized on
alternating weeks. Estrus synchronization was accomplished using a sequential treatment
of prostaglandin (PGF 2α ). During the breeding season, each female received two
injections of 10 mg PGF 2α (dinoprost tromethamine, i.m.) every 11 or 14 days as
modified from (Ott et al., 1980).
Blood Sampling and Radioimmunoassay (RIA)
Blood samples were collected for both Experiments 1 and 2 via jugular
venipuncture. For Experiments 1 and 2, blood samples were collected from bucks on a
125
weekly basis from September through January at 0800. For Experiment 2, blood samples
were also collected from the TP-treated wethers over a 48-hr period at the following time
points relative to the injection of TP: 0, 0.25, 0.5, 1, 2, 6, 12, 24, and 48 h. Serum was
stored at -20 °C until assayed.
Serum testosterone concentrations were determined by commercial RIA kit for
bucks (Beckman Coulter DSL-4000, Webster, TX), and for TP-treated wethers (Siemens
Healthcare Diagnostics, Inc., Coat-A-Count Total Testosterone, Los Angeles, CA)
validated in our laboratory for goat serum. The minimum detection limit of the DSL-4000
assay was 0.02 ng/ml and the inter-assay coefficient of variation was 12%. The minimum
detection limit of the Coat-A-Count Total Testosterone assay was 0.002 ng/ml and the
inter-assay coefficient of variation was 9%.
Experiment 1:
To examine if males invest differentially depending upon reproductive
opportunities available, males were housed under different circumstances and blood
samples were taken as previously described.
Housing Conditions
Beginning on August 4, prior to the onset of the breeding season, bucks were
randomly assigned to live in one of two housing conditions. One group of bucks was
housed with fence-line and visual contact with females (Near bucks, n=5). Females
housed next to males were estrus synchronized throughout the study. The other group of
bucks was housed with no visual and no fence-line contact with females (Far bucks, n=5).
After 10 wk, the Far bucks were moved to live with the Near bucks so all bucks had
126
fence-line contact with females. All males remained living together, with fence-line
contact to females for the remainder of the breeding season.
Experiment 2:
To examine if maintaining high T concentrations is costly for males, body
weights were measured for both intact and T replaced males during the breeding season.
Males
Bucks (n=6) and T replaced wethers (n=13) were utilized to examine body weight
change (representing physiological costs) and correlated T concentrations.
Testosterone Propionate Treatment
Wethers were randomly assigned to one of three testosterone propionate (TP;
A7000-000 Steroids, Inc. Newport, RI) treatment groups: vehicle control (CON, n=3), 25
mg (n=5), and 100 mg (n=5). TP-treated males received TP (s.c.) 3x/week beginning
August 3. Research from previous studies by our laboratory have shown that 25 mg TP is
sufficient to activate male reproductive behaviors in castrated male goats (Longpre and
Katz, In Press). Injections continued for a total of 24 wk.
Male Diet
Bucks received 0.45 kg medicated feed (Calf Pellet with amprolium, 16% CP, 1.6
Mcal/lb NE M ; F.M. Brown's Sons, Inc, Birdsboro, PA) and ad libitum access to hay. TPtreated wethers initially received the same diet as the bucks. However, starting in
November the 100 mg and 25 mg TP-treated wethers were also supplemented with 0.23
kg non-medicated feed (Sheep and Goat Krunch, 16% CP, 1.6 Mcal/kg NE M ; F.M.
Brown's Sons, Inc, Birdsboro, PA) due to excessive weight loss. Males were not
127
individually fed. They were de-wormed every 3-4 weeks. All diets met or exceeded NRC
requirements (National Research Council, 2007).
Body Weights
Body weights were collected from bucks on a weekly basis at 0800, prior to the
grain meal, for one year using a digital scale (Mettler-Toledo Inc., Model 8520;
Columbus, OH). Body weights from the TP-treated wethers were collected from wethers
approximately every 3 months for one year using a digital scale (Mettler-Toledo Inc.,
Model 8520; Columbus, OH).
Statistics:
Serum T Concentrations: For Experiment 1, mean serum T concentrations were
determined from weekly samples collected during the breeding season. Mean T
concentration were determined for both the Near and Far bucks. Differences in mean
serum T concentrations between Near and Far bucks during the first 10 wks of the study
(Aug 4 to Oct 12) and after (Oct 12 to Jan 28) were compared using a t-test for
independent samples. Results were deemed significant at P<0.05 (NCSS Statistical
Software, 2001, Kaysville, UT).
For Experiment 2, mean T concentrations were determined for bucks during the
breeding and non-breeding season. Differences in mean serum T concentrations between
the breeding and non-breeding season were compared using a t-test for independent
samples. Results were deemed significant at P<0.05 (NCSS Statistical Software, 2001,
Kaysville, UT). For TP-treated wethers, T concentrations are represented as area under
the curve (AUC) for the 48-hr collection. A one-way ANOVA was completed and results
were deemed significant at P<0.05 (SAS Version 9.2, Cary, NC).
128
Body weights:
Weekly body weights for all six bucks were pooled by month and averaged.
Differences in body weights between the breeding and non-breeding season were
compared using a t-test for independent samples. Results were deemed significant at
P<0.05 (NCSS Statistical Software, 2001, Kaysville, UT). For the TP-treated wethers, trimonthly body weights are represented as mean values for each treatment group for the
TP-treated wethers. A one-way ANOVA was competed and results were deemed
significant at P<0.05 (SAS Version 9.2, Cary, NC).
129
RESULTS
Experiment 1
Weekly mean blood samples for the Near and Far bucks for the entire duration of
Experiment 1 are displayed in Figure 1. Near bucks had higher serum T concentrations
than the Far bucks for the first 10 wk of the experiment (P<.05; 1.2 ± 0.05 vs. 0.65 ± 0.3
µg·wk/ml, respectively) as shown in Figure 2. After fence-line contact with females, T
concentrations for the Far bucks increased and were similar to those of the Near bucks.
Mean serum T concentrations for samples collected two weeks prior and post move were
significantly different for the Far bucks, but there was no difference in T concentrations
for the Near bucks (P<.05; Fig. 3).
Experiment 2
Within our herd of bucks, when T concentrations are high, body weight is low
(Fig. 4). During the breeding season, mean body weights were 67.4 kg (SE = 0.9 kg) and
mean serum T concentrations were 9.56 ng/ml (SE = 1.29 ng/ml). During the nonbreeding season mean body weights increased by 6% and were 72.1 kg (SE = 0.7 kg) and
mean serum T concentrations were 1.75 ng/ml (SE = 0.15 ng/ml).
Wethers treated with 100 mg TP lost significant weight during the treatment
period from Jun 10 to Jan 25 (P<.05; Fig. 5). Body weights for the 100 mg TP-treated
wethers and the 25 mg TP-treated wethers were significantly different from pre-treatment
body weights on Mar 24th , 2 months after TP treatment was stopped. 100 mg TP-treated
wethers lost 17% of their original body mass and 25 mg TP-treated wethers lost 11% of
their original body weight. By Jun 17, approximately four months after TP treatment
ceased, 25 mg and 100 mg TP-treated males gained weight and had similar weights to
130
those prior to treatment. In contrast, body weights of CON wethers did not differ
throughout the study.
131
DISCUSSION
Males housed with fence-line and visual contact with females (Near
bucks) had higher T concentrations then males housed with no visual and no fence-line
contact to females (Far bucks) for the first 10 wk of the study. These data suggest that the
visual presence of females during the breeding season causes an increase and
maintenance of high circulating T concentrations. Due to the close visual proximity of
females, Near bucks likely maintained high T concentrations in the event that mating
could occur and the immediate display of a secondary sexual characteristic or behavior
response would be necessary. Similar increases above the seasonal increase in T
concentrations have also been found in cowbirds. Dufty and Wingfield (1986) found that
male cowbirds housed with females had higher T concentrations sooner and peak
concentrations were maintained for a longer duration of time than males housed
individually. Testosterone concentrations for the Far bucks increased and paralleled that
of the Near bucks after they were moved to have fence-line and visual contact with
females. The shorter photoperiod, stimulating the onset of the breeding season, may have
resulted in the initial increase in T concentrations for both of the Near and Far bucks
(Delgadillo et al., 2004; Delgadillo et al., 2006; Rivas-Munoz et al., 2007). The initial
rise in T concentrations may be necessary for initiation but not necessary for maintenance
of spermatogenesis and normal mating activity (D'Occhio and Brooks, 1982). After this
initial increase, T concentrations of the Far bucks likely fell due to lack of reproductive
opportunities. Schoech et al. (1996) found that male scrub-jays that delayed breeding,
Nonbreeders, had lower T concentrations but similar patterns of T production to males
that mated with females, Breeders. Nonbreeders that were exposed to sexually receptive
132
females showed increases in T concentrations greater than that of the Breeders,
suggesting that lack of reproductive opportunities resulted in the delay reproduction and
lower T concentrations for Nonbreeders. The increase in T concentrations, following
placement near females, represents an opportunistic reproductive response by the Far
bucks which may aid in maximizing lifetime reproductive success.
It is also possible that Near bucks maintained high T concentrations as a result of
male-male aggression. Pelletier et al. (2003) found that fecal T concentrations peaked
during pre-rut in a herd of bighorn sheep when the dominance hierarchy was being
established. Testosterone concentrations then fell from the pre-rut to the rut. Thus it
would be expected that T concentrations for both groups of bucks would show an initial
increase in followed by an immediate decrease. However this change in T concentrations
was only observed for the Far bucks while the Near bucks maintained elevated T
concentrations. Testosterone concentrations of the Near bucks may have been maximized
for the duration of the experiment due to the presence of females. Similarly, when the Far
bucks were moved to have fence line and visual contact to females, their T concentrations
likely increased to maximal concentrations for that time during the breeding season and
were similar to that of the Near bucks.
Plasticity in T production provides males with the ability to invest differentially in
reproductive effort depending on reproductive opportunities. Body mass loss for both the
bucks and TP-treated wethers was greatest when T concentrations were high. It has been
observed that male ungulates reduce fed intake during the breeding season (CluttonBrock, 1982; Coblentz, 1976; Geist, 1974; Miquelle, 1990; Newman et al., 1998).
However, CON males showed minimal changes in weight across the breeding season,
133
while the 100 mg and 25mg TP-treated males lost a significant amount of weight. This
suggests that weight loss was not due to seasonal change in photoperiod and resulting
decrease in feed intake by males as observed in other ungulates. Although not measured,
males with higher T concentrations likely were engaging in more T-dependent behaviors.
Males with higher T concentrations had increased energetic expenditure as a result of
increased T concentrations.
The dose-dependent relationship between T concentrations and body mass loss
suggests that there is a direct relationship between reproductive costs and male quality.
The 100mg TP-treated wethers lost an average of 17% initial body mass while wethers
receiving the lower 25 mg TP lost an average of 11% initial body mass. In a study
examining the effect of nutrition and the acute presence of females on T concentration in
male goats during the breeding season, Walkden-Brown et al. (1994) found that males
fed a low quality (LQ) diet had a lower T pulse frequency and intensity when a female
was presented compared to males on a high quality (HQ) diet. Further, males fed the LQ
diet had significantly lower body weights than the males fed the HQ diet. Differences in
T concentrations between males provided the HQ and LQ diets may be a result of
differences in male quality. Males provided the HQ diet could incur higher energetic
costs, associated with high T concentrations while males provided the LQ diet were
unable to afford such energetic costs. These finding suggests that maintenance of high T
concentrations is energetically costly to the male. Due to the high energetic costs, T
concentrations may serve as an honest indicator of fitness.
In summary, the cost of reproduction is important in shaping the life history traits
of males. Maintenance of high T concentrations is costly, thus T concentrations may
134
serve as an honest indicator of fitness. Variation in T concentrations provides males with
the ability to maximize reproductive success by modifying energetic costs depending on
male quality and reproductive opportunities available.
ACKNOWLEDGEMENTS
We would like to acknowledge Susan E. Becker for her excellent technical
assistance. We would also like to thank our Animal Science undergraduate students who
helped conduct this research. This work was supported by the NJ Agricultural
Experiment Station, project 06144.
135
Figure 1
Males housed near
or far from females
Mean Serum T Concentration (ng/ml)
25
All males housed
near females
Near bucks
Far bucks
20
15
10
5
0
Aug
Sep
Oct
Nov
Dec
Jan
Figure 1. Weekly serum T concentrations for Near and Far bucks during the
breeding season: Mean (±SEM) T concentrations for Near bucks (n=5) and Far bucks
(n=5) during the breeding season. Dashed lines indicate when males were moved to new
housing conditions.
136
Figure 2
1.4
*
Mean Serum T Concentrations
Area Under Curve (ug wk ml-1)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Far Bucks
Near Bucks
Figure 2. Near bucks have higher serum T concentrations then Far bucks: Mean
(±SEM) T concentrations for Near bucks (n=5) and Far bucks (n=5) during the first 10
wks of the breeding season. Testosterone concentrations are represented as area under the
curve for weekly collections. * Significant difference (P<0.05).
137
Figure 3
Mean Serum T Concentrations (ng ml-1)
18
16
prior to move
post move
*
14
12
10
8
6
4
2
0
Far Bucks
Near Bucks
Figure 3. Placement of Far bucks near females caused an increase in T
concentrations: Mean (±SEM) T concentrations for Near bucks (n=5) and Far bucks
(n=5) two weeks prior and two weeks following Far bucks move to be housed with the
Near bucks and have fence line contact and visual contact to females. * Significant
difference (P<0.05).
138
Figure 4
20
90
Serum T Concentration
Body Weight
Breeding Season
85
80
15
75
10
70
5
Pooled Mean Body Weight (kg)
Mean Serum T Concentration (ng/ml)
25
65
0
60
Oct
Dec
Feb
Apr
Jun
Aug
Figure 4. Weekly serum T concentrations and monthly body weights for six bucks:
Mean serum T concentrations and mean body weights (pooled by month) for six bucks
during the breeding and non-breeding seasons. T concentration pooled SE = 0.99 ng/ml.
Body weight pooled SE = 0.33 kg.
139
Figure 5
CON (n=3)
25 mg (n=5)
100 mg (n=5)
90
Mean Body Weight (kg)
85
a
a,b
80
a
a
a,b
a,b
75
b
a,b
70
c
c
65
60
Jun 10
Sep 23
TP treatment start
Jan 5
Mar 24
Jun 17
TP treatment end
Figure 5. Quarterly body weights of TP-treated wethers: Mean (± SEM) body
weights for TP-treated wethers. Red arrows indicate the beginning (Aug 3) and end (Jan
28) of treatment. a, b, c Bars with different superscripts differ only within treatments
(p<0.05).
140
REFERENCES
Albert, D. J., Jonik, R. H., Watson, N. V., Gorzalka, B. B., and Walsh, M. L., 1990.
Hormone-dependent aggression in male rats is proportional to serum testosterone
concentration but sexual behavior is not. Physiol Behav. 48, 409-416.
Andersson, M., 1982. Female choice selects for extreme tail length in a widowbird.
Nature. 299, 818-820.
Andersson, M., 1994. Sexual Selection. Princeton University Press, Princeton.
Arteaga, L., Bautista, A., Martinez-Gomez, M., Nicolas, L., and Hudson, R., 2008. Scent
marking, dominance and serum testosterone levels in male domestic rabbits.
Physiol Behav. 94, 510-515.
Bell, G., 1980. The costs of reproduction and their consequences. Am Nat. 116, 45.
Belliure, J., Smith, L., and Sorci, G., 2004. Effect of testosterone on T cell mediated
immunity in two species of mediterranean lacertid lizards. J Exp Zool Part A. 301,
411-418.
Buchanan, K. L., Evans, M. R., Goldsmith, A. R., Byrant, D. M., and Rowe, L. V., 2001.
Testosterone influences basal metabolic rate in male house sparrows: a new cost
of dominance signaling? Proc Roy Soc B. 268, 1337-1344.
Cavigelli, S. A., and Pereira, M. E., 2000. Mating season aggression and fecal
testosterone levels in male ring-tailed lemurs (Lemur catta). Horm Behav. 37,
246-55.
Clutton-Brock, T. H., 1982. The functions of antlers. Behaviour. 79, 108-125.
Clutton-Brock, T. H., and Vincent, A. C., 1991. Sexual selection and the potential
reproductive rates of males and females. Nature. 351, 58-60.
Coblentz, B. E., 1976. Functions of scent-urination in ungulates with special reference to
feral goats (Capra hircus L.). Am Nat. 110, 549-557.
D'Occhio, M. J., and Brooks, D. E., 1982. Threshold of plasma testosterone required for
normal mating activity in male sheep. Horm Behav. 16, 383-394.
Damassa, D. A., Smith, E. R., Tennent, B., and Davidson, J. M., 1977. The relationship
between circulating testosterone levels and male sexual behavior in rats. Horm
Behav. 8, 275-86.
Darwin, C., 1871. The descent of man, and selection in relation to sex. J. Murray,
London.
Delgadillo, J. A., Cortez, M. E., Duarte, G., Chemineau, P., and Malpaux, B., 2004.
Evidence that the photoperiod controls the annual changes in testosterone
secretion, testicular and body weight in subtropical male goats. Reprod Nutr Dev.
44, 183-193.
Delgadillo, J. A., Flores, J. A., Veliz, F. G., Duarte, G., Vielma, J., Hernandez, H., and
Fernandez, I. G., 2006. Importance of the signals provided by the buck for the
success of the male effect in goats. Reprod Nutr Dev. 46, 391-400.
Deutsch, C. J., Haley, M. P., and Le Boeuf, B. J., 1990. Reproductive effort of male
northern elephant seals: estimates from mass loss. Canadian Journal of Zoology.
68, 2580-2593.
Duffy, D. L., Bentley, G. E., Drazen, D. L., and Ball, G. F., 2000. Effects of testosterone
on cell-mediated and humoral immunity in non-breeding adult European starlings.
Behav Ecol. 11, 654.
141
Dufty, A. M., 1989. Testosterone and survival. Horm Behav. 23, 185-193.
Dufty, A. M., and Wingfield, J. C., 1986. The influence of social cues on the reproductive
endocrinology of male brown-headed cowbirds: field and laboratory studies.
Horm Behav. 20, 222-234.
FASS, 2010. Guide for the care and use of agricultural animals in research and
teaching, 3rd ed. Fed. Anim. Sci. Soc., Champagne, IL.
Fusani, L., 2008. Testosterone control of male courtship in birds. Horm Behav. 54, 227233.
Fusani, L., Day, L. B., Canoine, V., Reinemann, D., Hernandez, E., and Schlinger, B. A.,
2007. Androgen and the elaborate courtship behavior of a tropical lekking bird.
Horm Behav. 51, 62-8.
Fusani, L., and Hutchison, J. B., 2003. Lack of changes in the courtship behaviour of
male ring doves after testosterone treatment. Ethol Ecol Evol. 15, 143-157.
Galimberti, F., Sanvito, S., Braschi, C., and Boitani, L., 2007. The cost of success:
reproductive effort in male southern elephant seals (Mirounga leonina). Behav
Ecol Sociobiol. 62, 159-171.
Gaunt, A. S., Bucher, T. L., Gaunt, S. L. L., and Baptista, L. F., 1996. Is singing costly?
Auk. 113, 718-721.
Geist, V., 1974. On the relationship of social evolution and ecology in ungulates. Am
Zool. 14, 205-220.
Gentner, T. Q., and Hulse, S. H., 2000. Female European starling preference and choice
for variation in conspecific male song. Anim Behav. 59, 443-458.
Gosling, L. M., and Roberts, S. C., 2001. Scent-marking by male mammals: cheat-proof
signals to competitors and mates. Adv Stud Behav. 30, 169-218.
Graham, J. M., and Desjardins, C., 1980. Classical conditioning: induction of luteinizing
hormone and testosterone secretion in anticipation of sexual activity. Science.
210, 1039-1041.
Grossman, C. J., 1984. Regulation of the immune system by sex steroids. Endocr Rev. 5,
435.
Harding, C. F., and Follett, B. K., 1979. Hormone changes triggered by aggression in a
natural population of blackbirds. Science. 203, 918.
Hau, M., 2007. Regulation of male traits by testosterone: implications for the evolution of
vertebrate life histories. BioEssays. 29, 133-144.
Illius, A. W., Haynes, N. B., and Lamming, G. E., 1976. Effects of ewe proximity on
peripheral plasma testosterone levels and behaviour in the ram. Reproduction. 48,
25.
Jainudeen, M. R., McKay, G. M., and Eisenberg, J. F., 1972. Observations on musth in
the domesticated Asiatic elephant (Elephas maximus). Mammalia. 36, 247-261.
Kelso, E. C., and Verrell, P. A., 2002. Do male veiled chameleons, Chamaeleo
calyptratus, adjust their courtship displays in response to female reproductive
status? Ethology. 108, 495-512.
Ketterson, E. D., Nolan Jr, V., Cawthorn, M. J., Parker, P. G., and Ziegenfus, C., 1996.
Phenotypic engineering: using hormones to explore the mechanistic and
functional bases of phenotypic variation in nature. Ibis. 138, 70-86.
Ketterson, E. D., Nolan, V., Jr., Wolf, L., Ziegenfus, C., Dufty, A. M., Jr., Ball, G. F., and
Johnsen, T. S., 1991. Testosterone and avian life histories: the effect of
142
experimentally elevated testosterone on corticosterone and body mass in darkeyed juncos. Horm Behav. 25, 489-503.
Krebs, J. R., and Davies, N. B., 1978. Behavioural ecology: an evolutionary approach.
Sinauer Associates Inc., Massachusetts.
Leader-Williams, N., and Ricketts, C., 1982. Seasonal and sexual patterns of growth and
condition of reindeer introduced into South Georgia. Oikos. 38, 27-39.
Longpre, K. M., and Katz, L. S., In Press. Estrous female goats use testosteronedependent cues to assess mates. Horm Behav. doi:10.1016/j.yhbeh.2010.10.014
Mainguy, J., and Côté, S. D., 2008. Age-and state-dependent reproductive effort in male
mountain goats, Oreamnos americanus. Behav Ecol Sociobiol. 62, 935-943.
Marler, C. A., and Moore, M. C., 1988. Evolutionary costs of aggression revealed by
testosterone manipulations in free-living male lizards. Behav Ecol Sociobiol. 23,
21-26.
Marler, C. A., and Moore, M. C., 1989. Time and energy costs of aggression in
testosterone-implanted free-living male mountain spiny lizards (Sceloporus
jarrovi). Physiol Zool. 62, 1334-1350.
Marsh, J. A., and Scanes, C. G., 1994. Neuroendocrine-immune interactions. Poultry Sci.
73, 1049-1061.
McElligott, A. G.,Naulty, F.,Clarke, W. V., andHayden, T. J., 2003. The somatic cost of
reproduction: what determines reproductive effort in prime-aged fallow bucks?
Evol Ecol Res. 5, 1239-1250.
McGlothlin, J. W., Jawor, J. M., Greives, T. J., Casto, J. M., Phillips, J. L., and Ketterson,
E. D., 2008. Hormones and honest signals: males with larger ornaments elevate
testosterone more when challenged. J Evol Biol. 21, 39-48.
Miller, K. V., Marchinton, R. L., Forand, K. J., and Johansen, K. L., 1987. Dominance,
testosterone levels, and scraping activity in a captive herd of white-tailed deer. J
Mammal. 68, 812-817.
Miquelle, D. G., 1990. Why don't bull moose eat during the rut? Behav Ecol Sociobiol.
27, 145-151.
Moore, M. C., 1983. Effect of female sexual displays on the endocrine physiology and
behaviour of male white crowned sparrows, Zonotrichia leucophrys. J Zool. 199,
137-148.
Mougeot, F., Irvine, J. R., Seivwright, L., Redpath, S. M., and Piertney, S., 2004.
Testosterone, immunocompetence, and honest sexual signaling in male red
grouse. Behav Ecol. 15, 930-937.
Mougeot, F., Redpath, S. M., Piertney, S. B., and Hudson, P. J., 2005. Separating
behavioral and physiological mechanisms in testosterone-mediated trade-offs. Am
Nat. 166, 158-168.
National Research Council, 2007. Nutrient Requirements of Small Ruminants: Sheep,
Goats, Cervids, and New World Camelids. National Academy Press, Washington,
DC.
Newman, R. E., McConnell, S. J., Weston, R. H., Reeves, M., Bernasconi, C., Baker, P.
J., andWynn, P. C., 1998. The relationship between plasma testosterone
concentrations and the seasonal variation in voluntary feed intake in fallow bucks
(Dama dama). J Agr Sci. 130, 357-366.
143
Ott, R. S., Nelson, D. R., and Hixon, J. E., 1980. Fertility of goats following
synchronization of estrus with prostaglandin F2[alpha]. Theriogenology. 13, 341345.
Patricelli, G. L., Uy, J. A. C., Walsh, G., and Borgia, G., 2002. Sexual selection: male
displays adjusted to female's response. Nature. 415, 279-280.
Pelletier, F., Bauman, J., and Festa-Bianchet, M., 2003. Fecal testosterone in bighorn
sheep (Ovis canadensis): behavioural and endocrine correlates. Can J Zool. 81,
1678-1684.
Peters, A., 2000. Testosterone treatment is immunosuppressive in superb fairy-wrens, yet
free-living males with high testosterone are more immunocompetent. Proc Roy
Society B. 267, 883.
Pinxten, R., de Ridder, E., and Eens, M., 2003. Female presence affects male behavior
and testosterone levels in the European starling (Sturnus vulgaris). Horm Behav.
44, 103-109.
Purvis, K., and Haynes, N. B., 1974. Short-term effects of copulation, human chorionic
gonadotropin injection and non-tactile association with a female on testosterone
levels in the male rat. J Endocrinol. 60, 429-439.
Ramenofsky, M., 1984. Agonistic behaviour and endogenous plasma hormones in male
Japanese quail. Anim Behav. 32, 698-708.
Redpath, S. M., Mougeot, F., Leckie, F. M., and Evans, S. A., 2006. The effects of
autumn testosterone on survival and productivity in red grouse, Lagopus lagopus
scoticus. Anim Behav . 71, 1297-1305.
Rivas-Munoz, R.,Fitz-Rodriguez, G.,Poindron, P.,Malpaux, B., andDelgadillo, J. A.,
2007. Stimulation of estrous behavior in grazing female goats by continuous or
discontinuous exposure to males. J Anim Sci. 85, 1257-63.
Runfeldt, S., and Wingfield, J. C., 1985. Experimentally prolonged sexual activity in
female sparrows delays termination of reproductive activity in their untreated
mates. Anim Behav . 33, 403-410.
Ryser, J., 1989. Weight loss, reproductive output, and the cost of reproduction in the
common frog, Rana temporaria. Oecologia. 78, 264-268.
Schoech, S. J., Mumme, R. L., and Wingfield, J. C., 1996. Delayed breeding in the
cooperatively breeding Florida scrub-jay (Aphelocoma coerulescens): inhibition
or the absence of stimulation? Behav Ecol Sociobiol. 39, 77-90.
Seivwright, L. J., Redpath, S. M., Mougeot, F., Leckie, F., and Hudson, P. J., 2005.
Interactions between intrinsic and extrinsic mechanisms in a cyclic species:
testosterone increases parasite infection in red grouse. Proc Roy Soc B. 272,
2299-22304.
Stearns, S. C., 1989. Trade-offs in life-history evolution. Funct Ecol. 3, 259-268.
Trivers, R. L. (1972). Parental investment and sexual selection. In B. Campbell (Ed.),
Sexual Selection and the descent of man 1871-1971 pp. 136-179. Aldine Press,
Chicago.
Waitt, C., Little, A. C., Wolfensohn, S., Honess, P., Brown, A. P., Buchanan-Smith, H.
M., andPerrett, D. I., 2003. Evidence from rhesus macaques suggests that male
coloration plays a role in female primate mate choice. Proc Roy Soc Lond B Bio.
270, S144-S146.
144
Walkden-Brown, S. W., Martin, G. B., and Restall, B. J., 1999. Role of male-female
interaction in regulating reproduction in sheep and goats. J Reprod Fertil Suppl.
54, 243-57.
Walkden-Brown, S. W., Restall, B. J., Norton, B. W., and Scaramuzzi, R. J., 1994. The
"female effect" in Australian cashmere goats: effect of season and quality of diet
on the LH and testosterone response of bucks to oestrous does. J Reprod Fertil.
100, 521-31.
Wiley, C. J., and Goldizen, A. W., 2003. Testosterone is correlated with courtship but not
aggression in the tropical buff-banded rail, Gallirallus philippensis. Horm Behav.
43, 554-60.
Wingfield, J. C., 1984. Androgens and mating systems: testosterone-induced polygyny in
normally monogamous birds. Auk. 101, 665-671.
Wingfield, J. C., 1985. Short-term changes in plasma levels of hormones during
establishment and defense of a breeding territory in male song sparrows,
Melospiza melodia. Horm Behav. 19, 174-187.
Wingfield, J. C., Ball, G. F., Dufty Jr, A. M., Hegner, R. E., and Ramenofsky, M., 1987.
Testosterone and aggression in birds. Am Sci. 75, 602-608.
Wingfield, J. C., Hegner, R. E., Dufty Jr, A. M., and Ball, G. F., 1990. The" challenge
hypothesis": theoretical implications for patterns of testosterone secretion, mating
systems, and breeding strategies. Am Nat. 136, 829.
Wingfield, J. C., Lynn, S., and Soma, K. K., 2001. Avoiding the 'costs' of testosterone:
ecological bases of hormone-behavior interactions. Brain Behav Evol. 57, 239-51.
Wolff, J. O., 1998. Breeding strategies, mate choice, and reproductive success in
American bison. Oikos. 83, 529-544.
Yahr, P., and Thiessen, D. D., 1972. Steroid regulation of territorial scent marking in the
Mongolian gerbil (Meriones unguiculatus). Horm Behav. 3, 359-368.
Zahavi, A., 1975. Mate selection-a selection for a handicap. J Theor Biol. 53, 205-14.
Zahavi, A., 1977. The cost of honesty (further remarks on the handicap principle). J
Theor Biol. 67, 603-5.
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CHAPTER VI
DISSERTATION CONCLUSIONS
146
DISSERTATION CONCLUSIONS
Examination of female mate choice in large mammalian species is limited.
However, evidence from others species suggests that females use a variety of attributes to
evaluate and distinguish amongst males; often preferring males with extravagant
secondary sexual characteristics (reviewed in: Andersson, 1994). The goal of this
research was to determine if the domesticated goat (Capra hircus) can be used as a model
to study female mate choice for ungulate species. We wanted to specifically examine
what characteristics or cues females are using to distinguish among males. Further, we
also wanted to examine how characteristics and cues displayed by the male are regulated.
For many species, testosterone (T) regulates the expression of a large suite of
male secondary sexual characteristics (reviewed in: Hau, 2007; Rhen et al., 1999) and
imposes high energetic (Buchanan et al., 2001; Wingfield et al., 2001), and
immunosuppressive (Folstad and Karter, 1992; Marsh, 1992; Marsh and Scanes, 1994;
Penn and Potts, 1998) costs to the male. Accordingly, high T concentrations may serve as
an honest indicator of a male’s fitness. The objectives of the studies described in Chapter
II were to examine if females use T-dependent cues to assess potential mates. The results
of the research demonstrated females use T-dependent cues to assess potential mates
rather than morphological characteristics to distinguish among males. It is possible that
morphological characteristics may be less variable than other cues and, thus, may not be
an honest indicator of fitness as supported by findings from (Ball, 1940; Meyer et al.,
1988).
Building on the results from Chapters II, the objectives of the studies described in
Chapters III and VI were to examine if females are using males courtship (Chapter III)
147
and/or chemical (Chapter IV) cues to distinguish among males, and to determine if either
of these cues are T-dependent. Studies suggest that male courtship rate (Jiguet and
Bretagnolle, 2001; Knapp and Kovach, 1991; Vinnedge and Verrell, 1998), frequency
(Karino, 1995; Vinnedge and Verrell, 1998), and duration (Seymour and Sozou, 2009) of
display are sexually selected characteristics of courtship that are preferred among
females. Thus it was expected that females would prefer males that display higher
courtship rates and that courtship rate correlated to T concentrations, thus serving as an
honest indicator of a males overall fitness. Results from these studies support our
hypothesis that male courtship is a T-dependent characteristic that females use to
distinguish among males. Females did not distinguish between 25mg and 100mg TPtreated wethers, however, the courtship rate displayed between the 25mg and 100mg TPtreated wethers was similar. Likely, both groups exceeded a threshold concentration of T
required to display high courtship rates. Differences would likely occur in duration of
courtship behavior displayed as supported by findings from D'Occhio and Brooks (1982)
and Damassa et al. (1977), with high T males having the ability to court females for a
longer duration of time or display a larger repertoire of behaviors, keeping females in
close vicinity and obtaining multiple copulations.
The hypothesis tested in Chapter IV was that chemical cues provided by urine or
glandular secretions could be used by females to distinguish among males. Studies
suggest that chemical activity from glandular secretions (Iwata et al., 2000; Iwata et al.,
2001) and urine may be T-dependent (Goodwin et al., 2006; Lombardi et al., 1976;
Mendl et al., 2002; Rasmussen and Schulte, 1998; Whittle et al., 2000), but little work
has been done to understand the role of chemical cues for mate choice in ungulates.
148
Results from this study indicate that chemical cues may be T-dependent and females can
use chemical cues to distinguish among males.
The objective of Chapter V was to determine if T concentrations, and thus Tdependent cues, are an honest indicator of a male’s fitness. If T concentrations are an
honest indicator of a male’s fitness, then maintaining high T concentrations should
impose a cost to the male which are too high for a low quality male to incur (Zahavi,
1975; Zahavi, 1977). It is also expected that when reproductive opportunities are low,
males should maintain lower T concentrations as a means of avoiding the costs associated
with high T concentrations. Results from this study indicate that maintenance of high T
concentrations is costly as body mass loss was greatest for males with high T
concentrations. Males housed with fence-line contact to females had higher T
concentrations then those housed with no visual contact to females, suggesting that
variation in T concentrations provides males with the ability to maximize reproductive
success by modifying energetic costs depending on reproductive opportunities available.
Together, these data suggest that the female goat may be used as a model for the
study of female mate choice. Implications for this research may extend to a variety of
other ungulate species that are less accessible or endangered. The goal of future studies
should be focused on examining the relationship between female and male interactions.
Specifically, examine the relationship between male T concentrations and chemical cues.
Several studies suggest that chemical cues provided by the male act as primer
pheromones. Examination of “male effect” has shown that chemical cues or the presence
of the male causes an increase in luteinizing hormone, and eventual ovulation
(Chemineau, 1983; Martin et al., 1980; Oldham et al., 1979; Signoret, 1991; Walkden-
149
Brown et al., 1993). Observation of wild species has revealed that females are attracted to
male scent marks (Bowyer et al., 2007; Bowyer et al., 1998; Rasmussen and Schulte,
1998; Whittle et al., 2000) and chemical cues in these marks may act as primer
pheromones, and be necessary for reproduction (Miquelle, 1991). However, it is not clear
if females would elicit the same LH response or be attracted to scent marks if they were
distributed by a male with lower T concentrations. Examination of the threshold dose of
T required to elicit the “male effect” is necessary. Findings could confirm that females
are using olfactory cues to distinguish among male as they are only attracted to scent
marks from high quality males.
Future studies may also further examine the relationship between male quality
and T concentrations. Walkden-Brown et al. (1994) examined the effect of nutrition and
the acute presence of females on T concentration of male goats during the breeding
season. Results indicated that males fed a low quality (LQ) diet had a lower T pulse
frequency and intensity when a female was presented compared to males on a high
quality (HQ) diet. However, only acute differences rather than long-term differences in
male T concentrations were measured. To confirm that maintenance of high T
concentrations is energetically costly to the male a long term study is needed. Variables
can include diet with males fed either a low or high quality diet; the presence of females
with males housed near females or without visual contact to females; and duration of
placement near females. Placement near females prior to the breeding season (June) or
later in the breeding season (November) may cause males to maintain higher T
concentrations for a longer duration of time then what is normally observed. Examination
150
of the costs of maintaining high T concentrations may provide additional information
about male quality.
151
References
Andersson, M., 1994. Sexual Selection. Princeton University Press, Princeton.
Ball, J., 1940. The effect of testosterone on the sex behavior of female rats. J Comp
Psychol. 29, 151-165.
Bowyer, R. T., Bleich, V. C., Manteca, X., Whiting, J. C., and Stewart, K. M., 2007.
Sociality, mate choice, and timing of mating in American bison (Bison bison):
effects of large males. Ethology. 113, 1048-1060.
Bowyer, R. T., Manteca, X., and Hoymork, A. 1998. Scent marking in American bison:
morphological and spatial characteristics of wallows and rubbed trees, pp. 81-91.
In L. R. Irby and J.E. Knight (eds.). International Symposium on Bison Ecology in
North America. Bozeman, Montana.
Buchanan, K. L., Evans, M. R., Goldsmith, A. R., Byrant, D. M., and Rowe, L. V., 2001.
Testosterone influences basal metabolic rate in male house sparrows: a new cost
of dominance signaling? Proc Roy Soc B. 268, 1337-1344.
Chemineau, P., 1983. Effect on oestrus and ovulation of exposing creole goats to the
male at three times of the year. J Reprod Fertil. 67, 65-72.
D'Occhio, M. J., and Brooks, D. E., 1982. Threshold of plasma testosterone required for
normal mating activity in male sheep. Horm Behav. 16, 383-394.
Damassa, D. A., Smith, E. R., Tennent, B., and Davidson, J. M., 1977. The relationship
between circulating testosterone levels and male sexual behavior in rats. Horm
Behav. 8, 275-86.
Folstad, I., and Karter, A. J., 1992. Parasites, bright males, and the immunocompetence
handicap. Am Nat. 139, 603.
Goodwin, T. E., Eggert, M. S., House, S. J., Weddell, M. E., Schulte, B. A.,
and Rasmussen, L. E., 2006. Insect pheromones and precursors in female African
elephant urine. J Chem Ecol. 32, 1849-53.
Hau, M., 2007. Regulation of male traits by testosterone: implications for the evolution of
vertebrate life histories. BioEssays. 29, 133-144.
Iwata, E., Wakabayashi, Y., Kakuma, Y., Kikusui, T., Takeuchi, Y., and Mori, Y., 2000.
Testosterone-dependent primer pheromone production in the sebaceous gland of
male goat. Biol Reprod. 62, 806-810.
Iwata, E., Wakabayashi, Y., Matsuse, S., Kikusui, T., Takeuchi, Y., and Mori, Y., 2001.
Induction of primer pheromone production by dihydrogentestosterone in the male
goat. J Vet Med Sci. 63, 347-348.
Jiguet, F., and Bretagnolle, V., 2001. Courtship behaviour in a lekking species: individual
variations and settlement tactics in male little bustard. Behav Process. 55, 107118.
Karino, K., 1995. Male-male competition and female mate choice through courtship
display in the territorial damselfish Stegastes nigricans. Ethology. 100, 126-138.
Knapp, R. A., and Kovach, J. T., 1991. Courtship as an honest indicator of male parental
quality in the bicolor damselfish, Stegastes partitus. Behav Ecol. 2, 295-300.
Lombardi, J. R., Vandenbergh, J. G., and Whitsett, J., 1976. Androgen control of the
sexual maturation pheromone in house mouse urine. Biol Reprod. 15, 179.
Marsh, J. A., 1992. Neuroendocrine- immune interactions in the avian species: a review.
Poultry Sci Rev. 4, 129-167.
152
Marsh, J. A., and Scanes, C. G., 1994. Neuroendocrine-immune interactions. Poultry Sci.
73, 1049.
Martin, G. B., Oldham, C. M., and Lindsay, D. R., 1980. Increased plasma LH levels in
seasonally anovular Merino ewes following the introduction of rams. Anim
Reprod Sci. 3, 125-132.
Mendl, M., Randle, K., and Pope, S., 2002. Young female pigs can discriminate
individual differences in odours from conspecific urine. Anim Behav. 64, 97-101.
Meyer, H. H. D., Sauerwein, H., and O'Callaghan, D., 1988. Possible regulation of
muscle growth via estrogen and androgen receptors. Eur J Endocrinol. 117, S189.
Miquelle, D. G., 1991. Are moose mice? The function of scent urination in moose. Am
Nat. 138, 460-477.
Oldham, C. M., Martin, G. B., and Knight, T. W., 1979. Stimulation of seasonally
anovular Merino ewes by rams. I. Time from introduction of the rams to the
preovulatory LH surge and ovulation. Anim Reprod Sci. 1, 283-290.
Penn, D., and Potts, W. K., 1998. Chemical signals and parasite-mediated sexual
selection. Trends Ecol Evol. 13, 391-396.
Rasmussen, L. E., and Schulte, B. A., 1998. Chemical signals in the reproduction of
Asian (Elephas maximus) and African (Loxodonta africana) elephants. Anim
Reprod Sci. 53, 19-34.
Rhen, T., Ross, J., and Crews, D., 1999. Effects of testosterone on sexual behavior and
morphology in adult female leopard geckos, Eublepharis macularius. Horm
Behav. 36, 119-28.
Seymour, R. M., and Sozou, P. D., 2009. Duration of courtship effort as a costly signal. J
Theor Biol. 256, 1-13.
Signoret, J. P., 1991. Sexual pheromones in the domestic sheep: importance and limits in
the regulation of reproductive physiology. J Steroid Biochem Mol Biol. 39, 63945.
Vinnedge, B., and Verrell, P., 1998. Variance in male mating success and female choice
for persuasive courtship displays. Anim Behav. 56, 443-448.
Walkden-Brown, S. W., Restall, B. J., and Henniawati, 1993. The male effect in the
Australian cashmere goat. 2. Role of olfactory cues from the male. Anim Reprod
Sci. 32, 55-67.
Walkden-Brown, S. W., Restall, B. J., Norton, B. W., and Scaramuzzi, R. J., 1994. The
"female effect" in Australian cashmere goats: effect of season and quality of diet
on the LH and testosterone response of bucks to oestrous does. J Reprod Fertil.
100, 521-31.
Whittle, C. L., Bowyer, R. T., Clausen, T. P., and Duffy, L. K., 2000. Putative
pheromones in urine of rutting male moose (Alces alces): evolution of honest
advertisement? J Chem Ecol. 26, 2747-2762.
Wingfield, J. C., Lynn, S., and Soma, K. K., 2001. Avoiding the 'costs' of testosterone:
ecological bases of hormone-behavior interactions. Brain Behav Evol. 57, 239-51.
Zahavi, A., 1975. Mate selection-a selection for a handicap. J Theor Biol. 53, 205-14.
Zahavi, A., 1977. The cost of honesty (further remarks on the handicap principle). J
Theor Biol. 67, 603-5.
153
Curriculum Vita
Kristy M. Longpre
Education
2005 –2011
Rutgers University, New Brunswick, NJ
Doctor of Philosophy
Graduate Program: Endocrinology and Animal Biosciences
2001 – 2005
Rutgers University, Newark, NJ
Bachelor of Arts in Chemistry
Research Experience
2006 – Present
Graduate Student and Research Assistant
Rutgers University- New Brunswick, NJ
Advisor: Dr. Larry Katz
Thesis: Female mate choice using a French Alpine goat model
2007 – 2009
Data Monitor
AlcheraBio LLC- Metuchen, NJ
2004 – 2005
Laboratory Assistant
Rutgers Neuroscience Research Center- Newark, NJ
Teaching Experience
2010
Instructor
Careers in Animal Science (60 students/semester)
Introduction into Scientific Research (10 students/semester)
Rutgers University- New Brunswick, NJ
2009, 2010
Guest Lecturer
Douglass Science Institute: 9th-10th grade
Rutgers University- New Brunswick, NJ
Natural Selection and Animal Behavior (4 lectures- 25 students)
2008 – 2009
Teaching Fellow
National Science Foundation K-12 Program
Rutgers Science Explorer Bus (20 students/session)
Woodrow Wilson Middle School (25 students/class)
2005 – 2008, 2010
Teaching Assistant
Rutgers University- New Brunswick, NJ
Animal Nutrition (21 students/semester)
154
Systems Physiology Laboratory (50 students/semester)
Biology 101/102 Laboratory (50 students/semester)
2006 – 2007
Tutor
Rutgers University Educational Opportunity Fund Program- New
Brunswick, NJ
Chemistry 101/102 (3 students/semester)
Refereed Publications
Margiasso, M., Longpre, K.M., and Katz, L.S. (2010). Partner Preference: Assessing the
Role of the Female Goat. Physiology and Behavior, 99: 587-591.
Ludvig, E. A., Balci, F., Longpre, K. M. (2008). Timescale dependence in a conditional
temporal discrimination procedure. Behavior Processes, 77: 357-363.
Manuscripts In Press
Longpre, K.M. and Katz, L.S. Estrous females use testosterone dependent cues to assess
potential mates. Submitted to: Hormones and Behavior