Naturwissenschaften (2003) 90:141–144
DOI 10.1007/s00114-003-0404-9
SHORT COMMUNICATION
Julia Ostner · Michael Heistermann ·
Peter M. Kappeler
Intersexual dominance, masculinized genitals
and prenatal steroids:
comparative data from lemurid primates
Received: 30 July 2002 / Accepted: 19 January 2003 / Published online: 8 February 2003
Springer-Verlag 2003
Abstract Masculinization of female genitalia and female
intersexual dominance distinguish spotted hyenas (Crocuta crocuta) and Malagasy primates (Lemuriformes)
from most other mammals. An unusual prenatal endocrine
environment has been proposed to proximately underlie
the development of these traits in hyenas. To examine
whether female dominance and genital masculinization
are similarly enhanced by the prenatal environment in
lemurid primates, we measured androgen and estrogen
excretion in pregnant wild redfronted lemurs (Eulemur
fulvus rufus). Our results showed that estrogen levels
during the second phase of gestation were much higher in
females carrying a male fetus than in female-carrying
mothers. This may indicate the onset of testicular activity
in male fetuses, because androgens of fetal origin are
aromatized to maternal estrogens. Levels of androgen
excretion were similar in all mothers regardless of the
fetus’ sex, which may suggest that androgen-independent
mechanisms also contribute to female masculinization.
The much higher androgen/estrogen ratio in femalecarrying mothers indicates that relative, rather than
absolute, prenatal steroid concentrations may play a role
in female masculinization.
J. Ostner ()) · P. M. Kappeler
Abteilung Verhaltensforschung and kologie,
Deutsches Primatenzentrum, Kellnerweg 4, 37077 Gttingen,
Germany
e-mail: [email protected]
Tel.: +49-551-3851282
Fax: +49-551-3851228
J. Ostner
Lehrstuhl fr Tierkologie and Tropenbiologie,
Universitt Wrzburg, Germany
M. Heistermann
Abteilung Reproduktionsbiologie, Deutsches Primatenzentrum,
Gttingen, Germany
Introduction
In most mammals, adult males dominate females because
of their superior size, weapons and androgen-mediated
aggressiveness, all of which are by-products of intrasexual selection (Lande 1980; Moore 1990). In spotted
hyenas (Crocuta crocuta) and most primates of Madagascar, however, females clearly dominate males in
dyadic agonistic interactions and bear masculinized
genitalia (Petter-Rousseaux 1962; Frank 1986, 1997;
Kappeler 1993; East and Hofer 2001). Because adult
female spotted hyenas and lemurs do not exhibit higher
levels of androgens than males (von Engelhardt et al.
2000; Goymann et al. 2001), investigations of the
proximate basis underlying this unusual trait have shifted
towards endocrine mechanisms of prenatal masculinization. Spotted hyena fetuses do indeed experience high
levels of maternal androgens, particularly testosterone
(Yalcinkaya et al. 1993), from the first third of gestation
onwards (Frank et al. 1991; Glickman et al. 1992; Licht et
al. 1992) and the virilization of female genitalia and
female aggressiveness in this species have been attributed
to these high levels of prenatal androgens (Yalcinkaya et
al. 1993; Licht et al. 1998).
This mechanism has been questioned, however, by
pointing out that this unusual prenatal environment does
not have the same effects on males (see Goymann et al.
2001, p. 90), and experiments using prenatal application
of anti-androgens did not prevent the development of an
enlarged clitoris, suggesting that androgen-independent
mechanisms also contribute to the development of
masculinized female traits (Drea et al. 1998). High levels
of prenatal androgens in spotted hyenas may alternatively
have been selected to produce young primed for intense
sibling rivalry (East and Hofer 2002). Here we present the
first comparative information on prenatal endocrine
environment and genital masculinization from a preliminary study of prenatal steroids in wild redfronted lemurs
(Eulemur fulvus rufus).
Redfronted lemurs are sexually monomorphic, but
sexually dichromatic, primates from Madagascar that live
142
Fig. 1 Prenatal endocrine environments of male (M) and female (F) fetal Eulemur fulvus
rufus during early (E) and late
(L) gestation. Mean values
(+SD, n=6 samples per female
and gestation phase) of fecal
estrogen (black) and testosterone (white) excretion of three
male-carrying and two femalecarrying mothers are depicted
in small multi-male, multi-female groups. As in other
lemurs, females have an enlarged clitoris and the ability
to dominate males, but inter-sexual relations vary across
populations. Females of one wild population were able to
dominate some but not all males (Ostner and Kappeler
1999), while studies in captivity and on another wild
population revealed no evidence for dominance relations
among the sexes (Pereira et al. 1990; Pereira and
Kappeler 1997). In addition, female infants are strikingly
masculinized in that they initially bear the pelage pattern
of adult males (yellow-brown with red forehead), which
changes to the specific female pelage (reddish-brown with
white forehead) not before 2–3 months of life (personal
observation). We studied the potential prenatal hormonal
correlates underlying these sex differences by noninvasively assessing estrogen and androgen concentrations in pregnant females, using fecal hormone analysis,
and correlating these hormone levels with infant sex.
Materials and methods
We collected fecal samples from five adult females from Kirindy
Forest, western Madagascar, every fifth day during the early phase
(105–80 days prior to parturition) and the late phase (30–1 days
prior to parturition) of gestation, yielding six samples per female
and gestation phase. Mean gestation length in redfronted lemurs is
121.5 days (Izard et al. 1993). The females gave birth to three male
and two female offspring. Fecal samples were preserved in ethanol
and, following homogenization and extraction (Ziegler et al. 2000),
were measured for immunoreactive total estrogen and testosterone
concentrations, using antibodies raised against estradiol-17hemisuccinate-BSA and testosterone-3-(carboxymethyl)oximeBSA, respectively. While the estrogen antibody was non-specific
and provided a combined measure of estrone and estradiol-17b
(confirmed by HPLC analysis), according to the manufacturer’s
information, the testosterone antibody was more specific, showing
relatively low cross-reactivities with 5a-dihydrotestosterone
(16.0%) and androstenedione (2.1%). Details of the methods used
have been described elsewhere (Heistermann et al. 1993; Kraus et
al. 1999). Applications of the two assays have been reliably used to
provide information on fecal estrogen and androgen excretion in
redfronted lemurs (Ostner et al. 2002; J. Ostner and M. Heistermann, unpublished results). Descriptive statistics are reported as
means and standard deviations.
Results
We found that estrogen concentrations were low in all
five females during the early phase of gestation (62€25 ng/
g dry weight). During the late phase, however, the pattern
of estrogen excretion was strikingly different among
females, with male-carrying mothers showing a 30–60fold increase (3,087€714 ng/g dry weight, n=3) in
estrogen levels until birth (after which levels returned to
baseline values), whereas estrogen values in femalecarrying mothers remained near baseline values
(128€32 ng/g dry weight, n=2; Fig. 1). In contrast to
estrogen values, levels of excreted androgens were similar
in all females, irrespective of fetal sex, with low
concentrations
characterizing
early
pregnancy
(168€56 ng/g dry weight, n=5) and 4–8-fold elevated
levels during late gestation (900€202 ng/g dry weight,
n=5; Fig. 1).
Discussion
The lack of an estrogen increase during the early stages of
pregnancy has been associated with the absence of
estrogen-stimulating chorionic gonadotropin (Shideler
1983), apparently a unique characteristic of strepsirrhine
primates (Maston and Ruvolo 2002). However, as our
data show, during later stages of gestation, maternal
estrogen levels are clearly influenced by fetal sex (see
Shideler 1983). Given that the production (and excretion)
of maternal estrogen during pregnancy in primates and
143
most other mammals is dependent on aromatization of
androgen precursors of fetal origin (Albrecht and Pepe
1998), the increased levels of estrogens in male-, but not
female-carrying mothers during the second half of
gestation probably reflects the onset of fetal testicular
activity and androgen production. This notion is consistent with morphological findings in closely related ruffed
lemurs (Varecia variegata), where testicular hyperplasia
and a high density of androgen-producing Leydig cells
have been found in late-gestation male fetuses (Shideler
1983). The production of fetal testicular androgens is
essential for male sexual differentiation in mammals.
Estrogen production in redfronted lemurs thus appears
to deviate from anthropoid primates, in which the fetal
adrenal (and not the fetal testis) is the major source of
androgen precursors for the production of maternallyexcreted estrogens. The fact that female-carrying mothers
in redfronted lemurs did not exhibit elevated levels of
estrogens suggests that the fetal adrenal in this (and
possibly other) lemur species is not a major source of
maternal estrogen precursors. Instead, we suggest that the
fetal adrenal may be the source of the maternally-excreted
androgens, because elevated levels of fecal androgens
during advanced fetal development were found in all
pregnant females, regardless of the sex of their fetuses.
However, the possibility that the excreted androgens also
stem from other sources, such as the maternal adrenal,
cannot be excluded and it still has to be shown that the
fecal androgen measure specifically reflects metabolites
of authentic androgens.
Although the sources of origin of the androgens
excreted by the pregnant females therefore remain to be
established, our results indicate that the prenatal hormonal
environment is different for male and female redfronted
lemur fetuses. Firstly, female fetuses may experience
androgen levels similar to those of male fetuses, a finding
which is in contrast to other mammals, such as humans
(Meulenberg and Hofman 1991) and elephants (Duer et
al. 2002), in which circulating androgens are elevated in
mothers carrying a son. Secondly, female fetuses are
exposed to much lower levels of estrogens than male
fetuses, a phenomenon which has not been reported for
any other mammal except ruffed lemurs (Shideler et al.
1983), which also exhibit female dominance.
Given the developmental and organizing effects of
hormones, particularly androgens, during early development in mammals, it seems reasonable to assume that
relatively high levels of androgens to which female
redfronted lemur fetuses may be exposed are responsible
for the masculinization of female infants. This situation
converges strikingly with the prenatal endocrine environment of female spotted hyenas (Yalcinkaya et al. 1993).
Because the androgen/estrogen ratio was much higher in
mothers carrying a daughter, relative, rather than absolute, prenatal steroid concentrations may be of importance
in female masculinization. This idea is further supported
by the observation that androgen levels were not higher in
female-carrying mothers. Thus, as in the case of the
masculinized genitalia in female hyenas (Drea et al.
1998), androgen-independent mechanisms may contribute
to the development of enhanced aggressiveness and
female dominance in lemurs. Female dominance in
spotted hyenas may have evolved because females have
control over copulation, thus favoring selection for male
submission (East and Hofer 2002). Corroboration of our
preliminary results, using a larger sample size from
several lemur species and applying more direct methods
for endocrine assessment, is required to evaluate the
generality of this explanation, however.
Acknowledgements We thank M. Razafindrasamba and N.
Rabarjiaona for their help with fecal sample collection and A.
Heistermann for help in the laboratory. The manuscript was
substantially improved with the help of comments made by Oliver
Schlke and three anonymous referees. Financial support was
provided by the DFG (Ka 1082/4-1, 4-2). This study complies with
the current laws of the countries in which it was conducted.
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