ANIMAL BEHAVIOUR, 2006, 72, 487e502
doi:10.1016/j.anbehav.2006.02.008
Suppression of escape behaviour during mating in the
cricket Acheta domesticus
K . A . KI LLIA N, L. C. S NELL, R. A MM ARELL & T. O. CRI ST
Department of Zoology, Miami University
(Received 3 June 2005; initial acceptance 17 August 2005;
final acceptance 27 February 2006; published online 7 July 2006; MS. number: A10182)
We examined behavioural switching in the cricket Acheta domesticus. Animals are constantly exposed to
sensory information that must be integrated by the nervous system and transformed into an appropriate
behavioural response. Often, the same sensory inputs can play a crucial role in different behaviours. For
example, in isolated crickets, tactile activation of specific cercal sensory receptors can trigger escape, but
these same sensory inputs are also important during mating. We mechanically stimulated crickets before,
during and after copulation and found that most touch-evoked escape responses are suppressed in copulating males. The behavioural switch from escape to mating occurs following a male’s chemosensory contact with a female and requires the continued presence of the female for its full expression. We removed
the antennae from male and female crickets to examine whether chemosensory cues detected by the antennae are necessary for this escape suppression and mating initiation. Although the antennae are the primary source of this chemosensory information, we determined that the maxillary palps are another
important source. Removal of male antennae did not significantly impact mating success. The loss of
the female antennae, however, did have a significant negative effect on both female and male receptivity
and mating behaviour.
Ó 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Animals are exposed to a constant flow of sensory
information from their internal and external environments that must be integrated by the central nervous
system and transformed into an appropriate behavioural
response. Often, sensory inputs and central neurons can
be shared components of the neural circuits responsible
for the generation of different behaviours (Morton & Chiel
1994; Kristan & Shaw 1997). Accordingly, an animal
must be able to choose, based on the circumstances in
which it finds itself, how to respond to such shared inputs. Although the neural systems involved in the production of specific behavioural responses have been
well characterized in some cases, the underlying mechanisms contributing to this decision-making process are
still not well understood.
A hierarchical scheme has been used to explain the
process of behavioural choice where higher-ranking behavioural functions have precedence over, and are able to
Correspondence and present address: K. A. Killian, Department of
Zoology, Miami University, 212 Pearson Hall, Oxford, OH 45056, U.S.A.
(email: [email protected]). L. C. Snell is now at the Biology Department, McLennan Community College, 1400 College Drive, Waco, TX
76708, U.S.A.
0003e3472/06/$30.00/0
control the production of, lower-ranking behaviours
(Tinbergen 1950, 1951; Davis 1979). Such a hierarchical
arrangement can help to explain how an animal prioritizes its behavioural responses in the face of conflicting demands. The relatively simpler nervous systems and
stereotyped behaviours of invertebrates have provided researchers with an opportunity to directly investigate the
underlying mechanisms controlling this prioritizing of behaviour. For example, in the marine molluscs Pleurobranchaea (Davis et al. 1974a) and Clione (Norekian &
Satterlie 1996), the leech Hirudo (Misell et al. 1998) and
the crayfish Procambarus (Krasne & Lee 1988), feeding behaviour is considered to rank more highly than withdrawal in each animal’s behavioural repertoire since all
of these animals show a decrease in their response to mechanical stimulation while feeding. Mutual inhibitory interactions among the neural circuits responsible for the
production of conflicting behaviours influence this behavioural choice (Kovac & Davis 1980; Huang & Satterlie
1990; Jing & Gillette 1995, 2000; Norekian & Satterlie
1996; Esch & Kristan 2002). However, the position of a particular behaviour within an animal’s hierarchy is also flexible and dependent on an animal’s motivational state. For
example, feeding behaviour no longer has priority over
withdrawal or escape in a well-fed Pleurobranchaea (Davis
487
Ó 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
488
ANIMAL BEHAVIOUR, 72, 2
et al. 1977; Gillette et al. 2000), and a hormonally induced
repression of feeding behaviour has been shown to occur
in Pleurobranchaea during egg laying (Davis et al. 1974b).
We have been using a simple insect model, the cercal
sensory system of the cricket Acheta domesticus, to investigate behavioural choice and neural decision making. The
cerci, two cone-shaped sensory appendages located on
the terminal abdominal segment of orthopteran insects,
are covered by mechanosensory receptors that can trigger
escape behaviours such as running (Gras & Horner 1992),
kicking and jumping (Huber 1965; Dumpert & Gnatzy
1977). For example, when a cricket’s cerci are contacted
by a predatory wasp, touch-sensitive campaniform sensilla
are activated (Dumpert & Gnatzy 1977), resulting in defensive kicking of the metathoracic legs (Gnatzy & Heusslein 1986; Hustert & Gnatzy 1995). However, these
same cercal campaniform sensilla also stimulate cricket
mating behaviour (Snell & Killian 2000). Our goal was to
determine the underlying mechanism that allows these
same cercal sensory inputs to influence two such widely
conflicting behaviours as mating and escape.
Cricket mating behaviour consists of an orderly
sequence of events: male stridulation and pair formation;
courtship behaviour; copulation and transfer of the
spermatophore; and male guarding behaviour (Alexander
1961; Loher & Rence 1978; Loher & Dambach 1989;
Adamo & Hoy 1994). In this study, we focused on behavioural changes occurring during courtship and copulation.
Chemosensory antennal contact between a male and female cricket is usually sufficient to elicit courtship behaviour (Rence & Loher 1977; Hardy & Shaw 1983;
Balakrishnan & Pollack 1997). During this initial stage of
mating, the male produces courtship song, flattens his
body to the ground, and rocks rhythmically from side to
side in an attempt to stimulate female mounting. During
mounting, the female comes up behind the male and contacts his cerci with her maxillary palps. Instead of eliciting
defensive kicking or jumping, however, this contact triggers a ‘backward slipping’ motor response from the male
(Sakai & Ootsubo 1988). During backward slipping, the
male holds his body lowered towards the ground and
moves backward beneath the female as she mounts onto
his back. As she mounts, the male hooks his epiphallus
onto the female’s subgenital plate to transfer the spermatophore. It takes approximately 2.5 min for spermatophore transfer to be completed and during this time the
male holds his cerci adjacent to the female’s abdomen
where they produce small, repetitive flicking movements.
Tactile activation of campaniform sensilla on the male’s
cerci during these movements provides important feedback on female body position to the male’s motor circuitry
responsible for transfer, and the removal of these sensory
inputs can significantly decrease mating success (Snell &
Killian 2000).
In this study, we investigated the role of behavioural
context in an animal’s responsiveness to touch. First, we
hypothesized that mating would rank highly in the
cricket’s behavioural repertoire such that escape responses
to tactile stimulation would be suppressed during mating.
Huber (1965) reported that male Gryllus campestris crickets
show fewer kicking responses to tactile stimulation of the
cerci when courting a female. Here, we asked whether
there is a more widespread decrease in a mating male’s
touch-evoked escape responses. For example, tactile stimulation of the wings normally triggers jumping (Hiraguchi
& Yamaguchi 2000), however, this response must be suppressed during copulation in order for the female to assume her mounted position on the back of the male. To
test this hypothesis, we mechanically stimulated male
crickets before and during copulation on five different
body locations. Second, we tested the hypothesis that
the initiation of courtship song and behaviour by a male
would signify that a behavioural switch had occurred
and would be accompanied by a suppression of the male’s
touch-evoked escape responses. We also examined the role
of the female in the initiation of this switch. Finally, we
removed the antennae from male or female crickets to
determine whether chemosensory cues detected by the
antennae are needed to trigger a cricket’s switch from
escape to mating behaviour.
METHODS
Animals
We used male and female Acheta domesticus crickets in
all experiments. Immature crickets were raised in our laboratory culture or purchased from Fluker’s Cricket Farm,
Baton Rouge, Louisiana, U.S.A. Groups of approximately
50 immature males and females were housed together in
large clear plastic containers within an incubator with
controlled temperature (29 C) and light (12:12 h light:dark cycle) exposure. Upon reaching adulthood (10th instar), males and females with all body parts intact were
placed in individual plastic deli containers (8 cm high,
11 cm wide) and 10e21 days elapsed before they took
part in a mating trial. Isolated crickets were housed in incubators with other similarly stored crickets so that visual
and auditory, but not tactile, interactions were possible.
All crickets had free access to water and dry dog chow.
Behavioural Tests
For each mating trial, we randomly chose a pair of
isolated, virgin, age- and size-matched male and female
crickets. Each cricket was only used in one trial. Males
were only used if a spermatophore was present and calling
song was produced. We carefully placed (without direct
handling) each mating pair into a clear, round Plexiglas
arena (15 cm diameter). A removable piece of opaque Plexiglas in the centre of the arena separated the male from
the female. White paper on the floor of the arena provided
traction and was replaced after each trial. All trials were
performed at room temperature (20 C) under dim lights
during the last 6 h of the light cycle (1200e1800 hours),
when A. domesticus shows maximum sexual activity (Nowosielski & Patton 1963).
We allowed each mating pair to acclimate to the arena
for 15 min before removing the divider. Each trial was
given a 15-min time limit, with removal of the divider signalling the start of the trial. All control and experimental
mating pairs made physical contact during all trials.
KILLIAN ET AL.: BEHAVIOURAL SWITCHING IN CRICKETS
Successful pairs were pairs in which a spermatophore was
completely transferred from male to female within the allotted 15 min. Mating failure could occur at any one of the
four sequential steps within a trial, which we defined according to the male’s role in the mating sequence as
follows.
(1) Failure in courtship song (CS): the male failed to
produce continuous courtship song and to show the
lowered body posture and rhythmic rocking associated
with courtship.
(2) Failure in backward slipping (BWS): the female did
not successfully mount onto the back of the male. All males
produced courtship song and rhythmic rocking. Included
in these failures were pairs in which the male failed to
successfully back under the female as she tried to mount
him, as well as pairs in which the female did not show
interest, and thus never attempted to mount the male.
(3) Failure in hooking: the male was able to successfully
backward slip under the female as she mounted, but was
unable to attach his epiphallus to the female’s subgenital
plate.
(4) Failure in transfer: the male was unable to successfully thread and transfer the spermatophore to the
mounted female following successful hooking. Such failures were confirmed when the female dismounted without an attached spermatophore.
Mechanical stimulation
We mechanically stimulated male crickets with a small
(size zero), soft bristled paintbrush on five different body
locations: the distal antenna; the dorsal femur of the
mesothoracic leg; the dorsal femur of the metathoracic
leg; the dorsal surface of the two forewings at the point of
hinge overlap; or the dorsal surface of the cercus. To
prevent response habituation, paintbrush stimuli were
applied to each cricket with an interstimulus interval of at
least 10 s and in the following sequence: cercus, wings,
metathoracic leg, antenna, mesothoracic leg. The application of stimuli alternated between the left and right side of
the body such that all appendages on one side of the body
were stimulated before those on the opposite side. This
procedure ensured that at least 100 s would elapse before
the reapplication of paintbrush stimulation to each cercus, antenna or leg, while at least 40 s elapsed between
wing stimulations. The side to which stimuli were first applied varied between animals and was selected randomly.
We visually observed and recorded the behavioural
response of each animal to each mechanical stimulus.
One of six possible reactions could occur following
a mechanical stimulus: (1) forward locomotion; (2) backward locomotion; (3) jump (full extension of both metathoracic legs); (4) withdrawal; (5) kick (partial to full
extension of one metathoracic leg); or (6) no response.
We included as withdrawal responses a lateral movement
of the body or appendage away from the stimulus source
following mesothoracic or metathoracic leg stimulation,
a lateral withdrawal of the animal’s body away from
a touched cercus, or a lateral turning movement of the
animal’s head and/or body away from a stimulated
antennae. During copulation, some animals responded
to the paintbrush with a small jerking, or shivering,
movement of the body or stimulated appendage. We
called these slight movements ‘flinches’ and included
them with withdrawal responses. Occasionally, an animal
would move forward or backward a few steps before
eliciting a kick or a jump. In those cases, we considered
the kick or jump to be the primary response and only
included that response in our tabulations. Under some
experimental situations, a male could respond with
mating movements, such as backward slipping or abdominal hooking movements, during tactile stimulation.
Control mating pairs
Male and female crickets used in control mating trials
did not receive mechanical stimulation or any other
experimental manipulation. We used these mating pairs
(N ¼ 40) to determine an overall mating success rate,
a control level of failure for each stage of the mating sequence (Fig. 1), and a control duration for each stage of
the mating sequence (Table 3). Each trial was recorded
on videotape with a Videolab Flexcam camera and a Panasonic AG-1960 videocassette recorder.
Experiment 1: suppression of male escape behaviours
We hypothesized that all male touch-evoked escape
behaviours such as jumping, running and kicking would
be suppressed during copulation. To test this hypothesis,
we applied mechanical stimuli to male crickets at three
different time periods: before, during and immediately
after copulation. We used ‘premating’ stimuli to characterize and quantify the range of behavioural responses
shown by males before they came into contact with
a female and commenced mating behaviour, and to
determine the primary response evoked during mechanical stimulation of each of the five body regions. We used
‘during-mating’ stimuli to determine whether the occurrence of each of these characteristic responses was altered
during copulation. During-mating stimuli were applied to
each male during the period of spermatophore transfer
(i.e. female mounted on top of the male and male
epiphallus attached to the female). ‘Postmating’ stimuli,
stimuli applied to each male within 2e10 min of successful spermatophore transfer and female dismount, were
used to determine whether there was a return of each behavioural response to its premating level following a successful copulation.
Two groups of males were tested that differed in the
time the males received premating stimulation. In one
group (N ¼ 42), premating stimuli were applied 15e60 min
before initiation of a mating trial. Individual males were
placed into an arena and allowed to acclimate for
15 min before the onset of premating stimulation. Each
of the five selected body regions was stimulated five times
for a total of 25 premating stimuli delivered to each male.
Immediately following male stimulation, we placed the
opaque barrier in the centre of the arena and added a female cricket to the side opposite the male. Following
a 15e60-min period of acclimation, this barrier was removed. In the second group (N ¼ 40), we returned each
male to its container after it received premating stimulation and waited 24e48 h before allowing the male to
take part in a mating trial.
489
ANIMAL BEHAVIOUR, 72, 2
(a)
1
0.8
0.6
0.4
Proportion of pairs that successfully reached each mating stage
490
0.2
Control (40)
15–60 min (42)
24–48 h (40)
0
(b)
1
0.9
0.8
0.7
Control (36)
CS + Fem (54)
CS – Fem (42)
0.6
(c)
1
0.8
0.6
0.4
0.2
0
Contact
Control (40)
MAA (49)
FAA (53)
CS
BWS
Hooking
Transfer
Mating stage
Figure 1. Effect of (a) the time at which males received premating
tactile stimulation, (b) tactile stimulation of the male in the presence
(CS þ Fem) or absence (CS Fem) of the female and (c) male
(MAA) or female (FAA) antennae ablation on the proportion of mating pairs that successfully reached and completed each stage in the
mating sequence. Mating stages are shown in order of occurrence
and include: physical (i.e. chemosensory) contact; courtship song
(CS) with lowered posture and rhythmic rocking of the body; backward slipping (BWS) with female mounting; hooking of the male
epiphallus onto the female subgenital plate; transfer of the spermatophore. All control and experimental mating pairs made physical
contact during all trials. Numbers in parentheses indicate number of
individual mating trials within each group. The same group of control mating pairs was used in each comparison. Note that there are
fewer control pairs in (b) because only males that initiated courtship
behaviour (CS) were used in this comparison. Also note the different
scale in (b). Means 1 binomial SE are shown.
Experiment 2: activation of the behavioural
switch from escape to mating
Chemosensory contact between male and female
crickets elicits male courtship song and courtship behaviour (Rence & Loher 1977; Hardy & Shaw 1983;
Balakrishnan & Pollack 1997). We hypothesized that this
contact is necessary and sufficient to trigger the behavioural switch from escape to mating, and that the initiation of
courtship song and rhythmic rocking by a male would signify that a switch had occurred in that animal. To investigate the time to suppression of male escape behaviour and
the role of the female in this suppression, we recorded the
behavioural responses of three groups of male crickets to
mechanical stimulation.
(1) Courtship song with female present (CS þ Fem). We
used 54 mating pairs. The male of each pair was mechanically stimulated with a paintbrush immediately after
courtship song was elicited by male and female chemosensory contact. The female was allowed to stay in close proximity and have additional contact with the male
throughout stimulus application. Because our tactile stimulation of the male did not inhibit male or female mating
behaviour, a variable number of stimuli were delivered
(range 2e25) before the onset of male backward slipping
and female mounting, at which point we ended our stimulation of the male.
(2) Courtship song without female present (CS Fem).
We used 42 pairs of crickets. Immediately after male courtship song was elicited by chemosensory contact with the
female, we prevented further contact between each pair
by separating the male and female with the opaque divider. We then stimulated each male with a paintbrush
until a total of 25 stimuli were applied (five stimuli to
each of five body regions). Immediately upon completion
of stimulation, we lifted the divider and allowed the trial
to resume.
(3) No courtship song with female present (No CS þ
Fem). The males in these 10 mating pairs made chemosensory contact with a female, but failed to begin courtship
song and rhythmic rocking within the 15-min time limit
allotted for each trial. We began tactile stimulation of
each male at the end of the 15-min trial, and this stimulation was done in the presence of the female. We delivered
five stimuli to each of the five body regions for a total of
25 stimuli delivered to each male.
For the males of all three groups, each behavioural
response to a stimulus was placed into one of three
categories: escape response (forward locomotion, backward
locomotion, jumping, kicking, or withdrawal); mating
response (backward slipping or abdominal hooking movements); or no response. For male mating responses, hooking
consisted of upward thrusting movements of the abdomen,
and backward slipping was a backward movement that
occurred in conjunction with a lowered body posture.
Experiment 3: role of the antennae
Male and female antennal contact triggers courtship
song and intense posture in male crickets. To determine
whether chemosensory cues detected by the antennae are
necessary for successful mating, we removed the antennae
from male and female crickets 1e2 days after the adult
moult. Each animal was anaesthetized on ice for
10e15 min and microdissecting scissors used to sever
each antenna at its base. Each animal was then returned
to its container for an additional 9e20 days before taking
part in a mating trial.
KILLIAN ET AL.: BEHAVIOURAL SWITCHING IN CRICKETS
For these mating trials, we either paired antennalablated males (MAA) with control females (N ¼ 49), or
paired antennal-ablated females (FAA) with control males
(N ¼ 53). We did not apply paintbrush stimuli. We recorded each trial on videotape and measured the duration
of each mating stage and the number of physical contacts,
and the sites of those contacts, for each pair by analysing
slow motion frame-by-frame playback of each trial.
Data Analyses
Probability of success or failure across
the mating sequence
The probability that cricket pairs successfully completed
each step of the mating sequence was analysed as
a correlated binomial response variable. Each pair was
considered a subject, and the probability of successful
completion of each mating step (1 ¼ success, 0 ¼ failure)
within subjects was analysed as a repeated measures response. The response profiles of subjects were compared
among treatments and controls in three separate analyses:
(1) control and premating stimulus treatments (15e60 min
and 24e48 h); (2) control and the presence or absence of
the female on the responses of males that had initiated
courtship song (CS Fem and CS þ Fem); and (3) control
and antennal-ablation treatments (FAA and MAA).
Correlated binomial responses were analysed using
generalized estimating equations (Myers et al. 2002). Maximum likelihood estimation was first used to provide initial parameter estimates for the effects of treatment,
which assumes homogeneous variances. A revised empirical estimate of the standard errors was conducted using
a correlation matrix of the repeated observations. This approach, called quasilikelihood estimation because it involves an iterative procedure, results in larger estimates
of standard errors especially if repeated observations are
correlated (Myers et al. 2002). We used this approach to
analyse the three experiments using Proc GENMOD in
SAS 9.1 software (SAS Institute 2002, Cary, North Carolina, U.S.A.). The binomial variable of success or failure
at each mating step was modelled using the logit link
function. The control was set as the reference group for
parameter estimation. We used an autoregressive correlation matrix in SAS to account for the conditional dependence in the probability of success between adjacent
mating steps. To test for treatment differences in the probability of success, we performed pairwise contrasts
between treatments and the control using Wald’s chisquare test.
Comparison of behavioural responses before,
during and after mating
To determine whether the touch-evoked behavioural
responses produced by tactile stimulation of each of five
body regions were altered during and after mating, we
used one-way repeated measures analyses of variance
(ANOVA) with BonferronieDunn post hoc tests to compare the premating behavioural responses of male crickets
to their responses during and after mating (experiment 1).
Since we predicted that escape responses would decrease
and ‘no responses’ would increase during mating, we
tested the hypothesis that the occurrence of the six
possible behavioural responses would differ between the
two treatments (i.e. premating versus during-mating
stimulation or premating versus postmating stimulation).
In experiment 2, each behavioural response to a tactile
stimulus was placed into one of three categories: escape
response (forward locomotion, backward locomotion,
jumping, kicking, or withdrawal); mating response (backward slipping or hooking); or no response. A one-way
ANOVA with individual animals as subjects was performed
to determine whether the presence of courtship song was
necessary for the male’s switch from escape to mating
responses (comparison of CS þ Fem pairs to No CS þ Fem
pairs) and to determine whether the continued presence
of the female during a mating trial was necessary for
male escape suppression (comparison of CS þ Fem pairs
to CS Fem pairs). Data were subjected to arcsine
square-root transformation prior to analysis to stabilize
the variation in proportional responses across the entire
response range of each experiment (Neter et al. 1996).
ANOVA was performed using PROC GLM in SAS 9.1
(SAS Institute). We used ANOVAs so that we could test
the hypotheses of mating or treatment (courtship song
or female presence) effects as the mean proportional
response using individual animals as replicates. All values
are reported as means 1 SE unless otherwise indicated.
RESULTS
Experiment 1: Suppression of Male Escape
Behaviours During Mating
Males receiving tactile stimulation 24e48 h premating
The mating behaviour of male crickets that received
tactile stimulation 24e48 h before a mating trial was unaffected by this prior stimulation (Fig. 1a), with the proportion of mating pairs successfully reaching each stage of the
mating sequence and the overall mating success similar to
those of control pairs (Wald’s chi-square: c21 ¼ 0:23,
P ¼ 0.63). Of the 40 males that were stimulated 24e48 h
before their mating trials, 29 (73%) were able to successfully complete all stages of mating, whereas 31 of 40 control males (78%) mated successfully. In addition, the
proportion of experimental males that made the transition from hooking to successful completion of transfer
was not different from the unstimulated control males, indicating that paintbrush stimulation of the experimental
males during this stage had no effect on their ability to
transfer the spermatophore.
Behavioural responses elicited by tactile stimulation of
the antennae, mesothoracic legs, metathoracic legs, wings
and cerci before, during and after copulation for 28 of
these successful male crickets are shown in Fig. 2. Premating stimulation consisted of four to five stimuli delivered
to each of five body locations for a total of 694 stimuli delivered to these 28 males. Premating stimulation of each
body part produced a primary, or dominant, behavioural
response (Fig. 2). Most premating stimuli applied to the
antennae produced either no discernible evasive response
491
ANIMAL BEHAVIOUR, 72, 2
1
Antennae
0.75
***
Pre
During
Post
**
0.5
**
0.25
**
0
1
0.75
Meso
Legs
*
***
0.5
***
0.25
Proportion of behavioural occurrences
492
0
*
**
***
1
0.75
***
Meta
Legs
*
0.5
0.25
0
*
***
*
***
**
**
1
Wings
0.75
**
0.5
0.25
0
1
ND
ND
ND
ND
ND
Cerci
ND
***
0.75
0.5
0.25
0
***
Fwd Loc
Bwd Loc
** **
Jump
Withdraw
***
Kick
No Resp
Figure 2. Comparison of the touch-evoked behavioural responses of successfully mated males (N ¼ 28) that had received premating stimulation 24e48 h before their mating trials (Pre) to their responses during spermatophore transfer (During) and within 10 min after female dismount with a spermatophore (Post). The proportion (mean 1 SE) of touches resulting in forward locomotion (Fwd Loc), backward
locomotion (Bwd Loc), jumping, withdrawal, kicking, or no response (No Resp) is shown for each of five different body locations. Mating responses, such as backward slipping or abdominal hooking movements, were never observed in these males. ND ¼ not determined: wings
could not be touched because of the mounted position of the female. *P < 0.05; **P < 0.01; ***P < 0.001.
from the animal, or a withdrawal of the animal’s head or
body away from the stimulus source. Withdrawal of the
leg or body occurred most often during premating stimulation of the mesothoracic legs, whereas the primary responses to metathoracic leg stimulation were forward
locomotion and jumping. Tactile stimulation of the wings
primarily evoked jumping responses whereas a tactile
stimulus applied to a cercus usually resulted in the male
moving forward away from the stimulus or kicking the
paintbrush with the ipsilateral metathoracic leg (Fig. 2).
KILLIAN ET AL.: BEHAVIOURAL SWITCHING IN CRICKETS
Mating responses, such as backward slipping or abdominal hooking movements, were never observed during premating stimulation.
During copulation, there was a significant decrease in
most touch-evoked escape responses, with the majority of
paintbrush stimuli producing no visible response from
these animals (Fig. 2, see Table 1 for test statistics). Since
spermatophore threading and transfer is completed by
the male in approximately 2.5 min (Snell & Killian
2000), we were only able to successfully deliver
12.5 0.5 stimuli (range 8e17 stimuli) to each animal
during this stage of mating, for a total of 352 stimuli delivered to these 28 males. The wings could not be stimulated
because of their position beneath the mounted female.
During copulation, 26 of the 154 stimuli (16.9%) applied
to the mesothoracic and metathoracic legs of these
males resulted in small flinching movements, which we
Table 1. Analysis of the proportion of total touch-evoked responses
of 28 successful male crickets stimulated 24e28 h prior to a mating
trial to their responses during and after copulation (ANOVA)
During mating
F
df
Antennae
Fwd Loc
Bwd Loc
Jump
Withdraw
Kick
No Resp
1.00
2.17
d
14.55
d
22.28
1,13
1,13
1,13
1,13
1,13
1,13
Meso Legs
Fwd Loc
Bwd Loc
Jump
Withdraw
Kick
No Resp
10.20
5.95
33.71
15.86
d
77.89
P
Postmating
F
df
P
0.34
0.16
d
0.002
d
0.0004
3.24
0.38
0.00
7.89
d
7.96
1,27
1,27
1,27
1,27
1,27
1,27
0.08
0.54
1.00
0.009
d
0.009
1,25
0.004
1,25
0.02
1,25 <0.0001
1,25
0.0005
1,25
d
1,25 <0.0001
1.33
0.11
1.12
6.78
d
1.00
1,27
1,27
1,27
1,27
1,27
1,27
0.26
0.75
0.30
0.01
d
0.33
Meta Legs
Fwd Loc 158.68 1,27 <0.0001 6.84 1,27 0.01
Bwd Loc
7.36 1,27
0.01
7.16 1,27 0.01
Jump
28.81 1,27 <0.0001 12.24 1,27 0.002
Withdraw
0.25 1,27
0.62
0.40 1,27 0.53
Kick
12.31 1,27
0.002
1.51 1,27 0.23
No Resp 239.82 1,27 <0.0001 0.00 1,27 0.98
Wings
Fwd Loc
Bwd Loc
Jump
Withdraw
Kick
No Resp
ND
ND
ND
ND
ND
ND
Cerci
Fwd Loc
67.34
Bwd Loc
1.00
Jump
11.78
Withdraw
0.19
Kick
70.71
No Resp 322.76
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
1,27 <0.0001
1,27
0.33
1,27
0.002
1,27
0.66
1,27 <0.0001
1,27 <0.0001
0.99
2.25
9.70
3.37
1.00
0.33
1,27
1,27
1,27
1,27
1,27
1,27
0.33
0.15
0.004
0.08
0.33
0.57
1.61
0.00
8.42
0.04
0.05
0.01
1,27
1,27
1,27
1,27
1,27
1,27
0.22
1.00
0.007
0.84
0.82
0.90
Fwd Loc: forward locomotion; Bwd Loc: backward locomotion; No
Resp: no response. See text for definition of responses; Dash: did
not occur; ND: not determined. Not all males received the full complement of touches during copulation.
tabulated as withdrawal responses. These flinches, which
accounted for 100% of withdrawal responses observed in
response to leg stimulation during spermatophore transfer, were not observed during premating or postmating
stimulation of the male. Postmating stimulation of these
28 males (N ¼ 698 total stimuli) revealed that the proportional occurrence of most responses returned to premating
levels following female dismount (Fig. 2, Table 1). However, a decrease in touch-evoked jumping responses relative to premating levels was observed for all five body
locations, with this decrease significant for metathoracic
leg, wing and cercal stimulation (Fig. 2, Table 1). As during
premating stimulation, all stimuli applied during and after
copulation failed to evoke mating responses in these
males.
Males receiving paintbrush stimulation
15e60 min premating
Significantly fewer males that received paintbrush stimulation 15e60 min before a mating trial were able to complete all stages of mating and successfully transfer
a spermatophore to a female (Fig. 1a) when compared to
both unstimulated control males (Wald’s chi-square:
c21 ¼ 5:67, P ¼ 0.02) and to males stimulated 24e48 h before their mating trials (Wald’s chi-square: c21 ¼ 3:94,
P ¼ 0.047). Most failures occurred at the first two stages
of mating (Fig. 1a), with nine of the 42 males failing to initiate courtship behaviour even after multiple contacts
with a female, and an additional nine pairs failing during
backward slipping and female mounting.
We used paintbrush stimuli to determine whether the
successful 15e60-min prestimulated males would show
escape suppression during copulation. We delivered a total
of 550 premating stimuli (25 stimuli per animal) to the 22
successful males in this group. Premating stimuli applied
to each body region evoked one or two primary responses
and the proportional occurrence of each response was
similar to that observed for males receiving 24e48 h of
premating stimulation (data not shown). We delivered
281 stimuli (12.8 0.9, range 4e20 stimuli) to these 22
males during copulation and found a significant decrease
in all of the primary touch-evoked escape responses (data
not shown). Instead, most stimuli evoked no discernible
response (X SE proportion of no responses: antennae,
1.0 0.0; mesothoracic legs, 0.85 0.07; metathoracic
legs, 0.92 0.03; wings, not determined; cerci, 0.99 0.06). Flinches were the only response we observed
when these males were stimulated during copulation. As
with 24e48-h prestimulated males, paintbrush stimulation had no effect on the ability of the 15e60-min males
to successfully complete transfer (Fig. 1a). We also stimulated these males after female dismount (25 per animal
for a total of 550 stimuli). Again, as with males stimulated
24e48 h before mating, the proportional occurrence of
most responses returned to premating levels once transfer
was complete (data not shown). However, these males also
showed a decrease, relative to premating levels, in the proportion of jumping responses evoked by stimulation of all
five body regions, with this decrease significant for mesothoracic leg (ANOVA: F1,21 ¼ 5.17, P ¼ 0.03) and wing
(ANOVA: F1,21 ¼ 6.30, P ¼ 0.02) stimulation, and not
493
494
ANIMAL BEHAVIOUR, 72, 2
quite significant for cercal stimulation (ANOVA:
F1,21 ¼ 3.08, P ¼ 0.09). All stimuli delivered either before,
during, or after copulation also failed to evoke mating
movements in these males.
Experiment 2: Activation of the Behavioural
Switch from Escape to Mating
Since we found that most touch-evoked responses were
inhibited in copulating males, we asked whether courting
males would also show this suppression. We hypothesized
that male escape suppression would occur in conjunction
with the initiation of male courtship song and behaviour.
We used three groups of mating pairs to test this idea. In
the CS þ Fem group, male crickets were tactilely stimulated immediately after the initiation of courtship song
and in the presence of a female. All stimuli were applied
to these males prior to mounting of the female. In the
CS Fem group, the male was separated from the female
by an opaque barrier immediately after courtship song initiation and then stimulated. In the No CS þ Fem group,
we recorded the touch-evoked behavioural responses of
males that failed to produce courtship song even after
multiple contacts with the female and so never progressed
into the mating sequence. These males were stimulated in
the presence of the female.
Application of paintbrush stimuli to courting males did
not affect the subsequent ability of these males to
copulate. The proportion of CS þ Fem pairs and control
pairs that successfully transferred a spermatophore
(Fig. 1b) was not significantly different (Wald’s chi-square:
c21 ¼ 1:07, P ¼ 0.30). Similarly, the mating success of pairs
in which males were stimulated in the absence of the female but immediately after the initiation of courtship
(CS Fem; Fig. 1b) was not significantly different from
that of control pairs (Wald’s chi-square: c21 ¼ 0:87,
P ¼ 0.35) or CS þ Fem pairs (Wald’s chi-square: c21 ¼ 0:00,
P ¼ 0.97).
We compared the proportion of escape responses,
mating responses, or no responses elicited by tactile
stimulation of the males for the successful CS þ Fem, successful CS Fem, and the No CS þ Fem mating pairs
(Fig. 3, Table 2). Since we did not act to prevent male backward slipping and female mounting during our application of paintbrush stimuli to the CS þ Fem males,
a variable number of stimuli were applied to each male
(8.71 0.93 stimuli/animal, range 2e25 stimuli) and
some males did not receive tactile stimulation to all five
body locations. In contrast, because the males of the
CS Fem pairs were separated from the females during
tactile stimulation, we were able to apply 25 stimuli, five
to each of the five body parts, to each male before we removed the barrier and allowed each pair to continue mating. The males that failed to initiate courtship song were
stimulated in the presence of the female (No CS þ Fem),
however, because these pairs never initiated mating behaviour, we were also able to apply 25 stimuli to each of
these 10 males.
Courting males stimulated in the presence of the female
showed significantly fewer escape responses than courting
males that were separated from the female when
stimulated or than males that failed to initiate courtship
(Fig. 3, Table 2). Mating responses were only observed in
CS þ Fem males and primarily occurred in response to tactile stimulation of the wings or cerci (Fig. 3). Of the 109
total stimuli applied to the cerci of CS þ Fem males, 41
(38%) resulted in backward slipping while only one stimulus produced hooking. In contrast, the only mating response shown by these males to wing stimulation was
hooking, with 57 (60%) of the 95 total stimuli applied
to the wings producing this response.
We also compared the specific escape responses evoked
by tactile stimulation of the wings and cerci. Tactile
stimulation of the cerci of CS Fem and No CS þ Fem
males produced significantly more forward locomotion
(ANOVA: F2,94 ¼ 11.32, P < 0.0001) and kicking (ANOVA:
F2,94 ¼ 10.59, P < 0.0001) responses than stimuli applied
to the cerci of CS þ Fem males (data not shown). During
wing stimulation, the only escape response shown by
CS þ Fem males was forward locomotion. In contrast,
both CS Fem males and No CS þ Fem males had a
tendency to respond with more forward locomotion
(ANOVA: F2,93 ¼ 2.68, P ¼ 0.07) and significantly more
backward locomotion (ANOVA: F2,93 ¼ 15.73, P < 0.0001)
and jumping (ANOVA: F2,93 ¼ 15.22, P < 0.0001) responses
to wing stimulation than did CS þ Fem males (data not
shown).
Experiment 3: Role of the Antennae
To determine whether chemical cues detected by the
antennae are required to trigger the successful transition
from escape to mating behaviour, we removed both
antennae from male or female crickets and determined
the effect that this antennal ablation had on subsequent
mating success (Fig. 1c). For all control and experimental
mating pairs that we tested, physical (i.e. chemosensory)
contact between the male and female was required for
courtship behaviour to be initiated, and we used the first
expression of courtship song in conjunction with lowered
body posture by the male of each mating pair as our criterion for mating initiation. Visual cues alone were never
sufficient to initiate courtship behaviour.
Significantly fewer pairs in which the females lacked
antennae (FAA) were able to successfully complete all
stages of mating when compared to both control pairs
(Wald’s chi-square: c21 ¼ 22:39, P < 0.0001) and male
antennal-ablated (MAA) pairs (Wald’s chi-square: c21 ¼
12:01, P ¼ 0.0005). The majority of the 39 FAA pairs that
failed to mate did so at the first two stages of mating,
with 22 males failing to initiate courtship and 15 pairs failing at backward slipping and mounting (Fig. 1c). The 22
failures at courtship were not due to a lack of contact since
the number of contacts made by these unsuccessful pairs
(8.7 1.04, range 3e19) was similar to the number
made by the 14 successful FAA pairs characterized in Table
3 (10.9 1.6, range 3e25). Instead, eight of the 22 pairs
that failed at courtship did so because neither the male
nor the female was receptive, eight failed because the female was receptive and approached the male but the
male acted aggressively by jerking, chirping aggressively,
kicking or running forward in response to each contact
KILLIAN ET AL.: BEHAVIOURAL SWITCHING IN CRICKETS
1
Antennae
**
CS + Fem
0.75
No CS + Fem
CS – Fem
0.5
**
0.25
0
1
0.75
Meso
Legs
**
***
0.5
Proportion of behavioural occurrences
0.25
*
0
1
0.75
Meta
Legs
**
**
***
***
0.5
0.25
**
***
0
1
Wings
***
***
0.75
0.5
0.25
***
0
1
Cerci
0.75
***
***
***
0.5
0.25
0
Escape response
**
***
Mating response
No response
Figure 3. Courtship song (CS) and the presence of the female (Fem) are both required for the suppression of escape and activation of mating
behavioural responses to tactile stimulation. The touch-evoked responses of male crickets stimulated after the initiation of courtship song and in
the presence of the female (CS þ Fem, N ¼ 49) were compared to males that failed to initiate courtship in the presence of the female (No
CS þ Fem, N ¼ 10) and to males in which we removed the female immediately following the initiation of male courtship song (CS Fem,
N ¼ 40). The proportion (mean 1 SE) of touches resulting in escape behaviours (forward locomotion, backward locomotion, jumping, withdrawal, kicking), mating behaviours (backward slipping, hooking), or in no response is shown for each of five different body locations.
*P < 0.05; **P < 0.01; ***P < 0.001.
by the female. The remaining six pairs failed because the
male initially appeared receptive, following and repeatedly contacting the female with his antennae, but the female was not receptive and ignored the male. As a result,
the male never advanced into courtship song and courtship behaviour.
An additional 15 of the female antennal-ablated pairs
failed at the backward slipping/mounting stage of mating
(Fig. 1c). Even though all males reaching this stage performed courtship song, lowered body posture and rhythmic rocking, seven of the 15 pairs that failed did so
because the male would kick back or move forward away
495
496
ANIMAL BEHAVIOUR, 72, 2
Table 2. Analysis of effect of a lack of courtship song (CS) or absence
of the female (Fem) on the proportion of total male cricket touchevoked responses (ANOVA)
No CS þ Fem
F
Antennae
Escape
Mating
No Resp
df
2.17 1,44
d
1,44
2.17 1,44
P
CS Fem
F
df
P
0.15
d
0.15
10.69 1,74
0.90 1,74
12.26 1,74
Meso Legs
Escape
10.77 1,36
Mating
1.51 1,36
No Resp 9.62 1,36
0.002
0.23
0.004
36.29 1,66 <0.0001
6.17 1,66
0.02
31.86 1,66 <0.0001
Meta Legs
Escape
Mating
No Resp
0.007
d
0.007
16.57 1,75
d
1,75
16.57 1,75
8.05 1,45
d
1,45
8.05 1,45
0.002
0.35
0.001
0.0001
d
0.0001
Wings
Escape
53.01 1,54 <0.0001 114.63 1,84 <0.0001
Mating 20.51 1,54 <0.0001 83.11 1,84 <0.0001
No Resp 0.51 1,54
0.48
0.37 1,84
0.55
Cerci
Escape
41.63 1,55 <0.0001
Mating
9.18 1,55
0.004
No Resp 2.51 1,55
0.12
46.20 1,85 <0.0001
37.20 1,85 <0.0001
0.01 1,85
0.92
No Resp: no response; Dash: did not occur. Not all CS þ Fem males
received the full complement of touches for this comparison.
from the female when she approached the male from behind and contacted his cerci or abdomen with her palps.
The remaining eight pairs failed because the female did
not attempt to mount. Instead, antennal-ablated females
often appeared agitated, spending the majority of the trial
walking around the perimeter of the arena and attempting
to climb up the arena wall.
In contrast, mating pairs in which the male was
antennal ablated tended to be less successful at mating
than control pairs, with 13 of the 49 antennal-ablated
males failing to initiate courtship compared to four of 40
Table 3. Effect of male (MAA) or female (FAA) antennal ablation on
cricket mating behaviour
Control
(N¼30)
MAA
(N¼28)
Mating stage duration (s):
ContacteCS
79.112.3a 78.918.3a
CSeBWS
30.98.5
58.316.4
10.70.8b
BWSeHk
9.00.9a
HkeTransfer
194.714.6 185.114.2
Total
313.720.4a 332.927.1a
Contacts needed
2.30.3a
3.40.5a
to evoke CS
FAA
(N¼14)
243.644.1b
117.055.7
11.40.8b
194.514.2
566.570.0b
10.91.6b
All values are means SE. Different superscript letters indicate significant differences between values within a row. CS: courtship song;
BWS: backward slipping; Hk: hooking; Total: total time from initial
contact to completion of transfer. See text for a complete description
of each mating stage.
control males (Fig. 1c); however, this difference was not
significant (Wald’s chi-square: c21 ¼ 3:53, P ¼ 0.06). Again,
these failures were not due to a lack of chemosensory contact, with these 13 pairs making 13.6 1.59 contacts
(range 4e23) during the 15-min trial. Of the 13 pairs
that failed at courtship, five failed because neither the
male nor the female was receptive, whereas the remaining
eight failed because the male would kick, run and aggressively chirp and jerk his body when contacted by the
female.
To examine more closely the influence of antennal
sensory inputs in mating success, we compared the
duration of each stage of mating for successful control
pairs and male antennal-ablated and female antennalablated pairs (Table 3). Female, but not male, antennal ablation significantly increased the amount of time that
elapsed between the first physical contact between a mating pair and the initiation of courtship song and courtship
behaviour by the male (ANOVA: F2,69 ¼ 7.30, P ¼ 0.001;
Table 3), as well as the number of actual physical contacts
required to evoke male courtship song (ANOVA:
F2,69 ¼ 25.44, P < 0.0001; Table 3). Four primary types of
physical contacts would usually occur between the male
and female of a mating pair: antennaleantennal (controls
only); antennalebody; palpsepalps; palpsebody. The part
of the body contacted was usually the wings. Palpebody
contact could be initiated by either the male or the female
of a mating pair. Control mating pairs primarily relied on
the antennae for sex recognition, with 85% of all contacts
made involving the antennae and only 15% the palps
(N ¼ 67 total contacts for 30 pairs). Male antennal-ablated
pairs relied more heavily on chemosensory information
from the palps, with 45% of all contacts (N ¼ 93 total contacts for 28 pairs) involving those appendages. In contrast,
72% of all contacts for mating pairs in which the female
was antennal ablated (N ¼ 153 contacts for 14 pairs) involved male antennal contact with the female wings,
head or legs while only 28% involved the palps, and
with the majority of palpal contacts initiated by the female. The majority of contacts were initiated by the intact
males of these pairs because the initial response of an antennal-ablated female was to ignore the male while he followed and antennated her as she moved about the arena.
Interestingly, the males of pairs in which either the male
or the female was antennal ablated tended to show more
aggressive responses than did control males, often chirping aggressively, jerking their bodies and kicking when
contacted by the female. These displays of aggression,
which did not occur as frequently during the mating trials
of control pairs, usually ended once courtship behaviour
was initiated by the males of the experimental pairs.
The mean time that elapsed from the first expression of
courtship song/lowered posture by the male to the
initiation of male backward slipping and female mounting
(CSeBWS, Table 3) was slightly longer and more variable
for experimental pairs, but did not differ significantly between the three groups (ANOVA: F2,69 ¼ 2.23, P ¼ 0.12).
This variability could be attributed to the failure by several
pairs at their first attempt at backward slipping either because the female overran the male during mounting, or
because she was improperly positioned at the start of
KILLIAN ET AL.: BEHAVIOURAL SWITCHING IN CRICKETS
mounting, causing the male to move forward as the female contacted his cerci, abdomen or leg with her palps.
Both antennal-ablated males and males attempting to
mate with an antennal-ablated female took significantly
longer to successfully attach, or hook, their epiphallus to
the female subgenital plate than did control males
(BWSeHooking; ANOVA: F2,69 ¼ 7.03, P ¼ 0.002; Table
3). At the start of backward slipping, intact males held
both antennae directed posteriorly towards the female.
As the female mounted and walked forward over the
male, the male would move his antennae forward until
the female’s head was positioned almost directly above
his head. Many antennal-ablated males, however, had difficulty in hooking because females would advance too far
forward. For female antennal-ablated pairs, more male
hooking attempts were also necessary because these females tended to be misaligned and misplaced laterally on
the back of the male during mounting. However, once
the male’s epiphallus was successfully hooked, the time it
took for transfer of the spermatophore (HookingeTransfer;
Table 3) did not differ significantly between the three
groups (ANOVA: F2,69 ¼ 0.37, P ¼ 0.69) even though
many of these experimental pairs remained misaligned. Finally, when total duration of trials was compared, only
pairs in which the female was antennal ablated took significantly longer to successfully mate (ANOVA: F2,69 ¼
9.78, P ¼ 0.0002; Table 3).
DISCUSSION
Touch-evoked Escape Behaviours
Tactile stimulation of the antennae, legs, wings and
cerci of nonmating male A. domesticus crickets evoked
a primary behavioural response when each body part
was touched. Responses could include simple avoidance
reflexes such as withdrawal of an appendage away from
the stimulus source, or more complex evasive responses
such as running, jumping or kicking. For example, isolated male crickets primarily responded to mesothoracic
leg stimulation with withdrawal of the leg or body and
to metathoracic leg stimulation with forward locomotion
or jumping. Insect legs are covered with touch-sensitive
hairs (Hustert 1985; Newland 1991), and activation of
such hairs probably triggered these reactions. Most stimuli
applied to the wings elicited jumping, as previously reported for the cricket Gryllus bimaculatus (Hiraguchi & Yamaguchi 2000). Small mechanosensory hairs on the
hindwings triggers this jumping (Hiraguchi et al. 2003)
and similar hairs are located on the basal region of the
cricket forewings (Fudalewicz-Niemczyk & Rosciszewska
1972), the point at which we stimulated the wings in
our experiments.
We found that most paintbrush stimuli applied to the
cricket antenna evoked no discernible escape response.
Tactile stimulation of the antennal flagellum of the cricket
often produces a lateral movement of the flagellum away
from the stimulus (Balakrishnan & Pollack 1997), however, we did not include such movements in our counts
of evasive withdrawal responses. The cockroach Periplaneta americana, in contrast, produces a fairly robust evasive
response when the antennae are touched (Comer et al.
1994). However, initiation of these responses may require
the activation of mechanoreceptors located in the basal
segments of the cockroach antennae rather than on the flagellum (Comer et al. 2003). Similar receptors have been
identified in the cricket (Kammerer & Honegger 1988;
Gebhardt & Honegger 2001), however, the low frequency
of evasive responses observed in our animals suggests
that tactile stimulation of the midregion of the antennae
usually does not activate these basal receptors. However,
it is also possible that our animals responded with an unusually low number of evasive responses to antennal stimulation because they were taken from populations that had
been cultured at high densities over several generations.
When we mechanically stimulated the cerci of male
crickets, the primary responses observed were kicking or
forward locomotion. Campaniform sensilla activated during tactile stimulation of the cerci are scattered over the
surface of each cercus (Killian et al. 1993) and can trigger
kicking of the cricket’s metathoracic legs (Dumpert &
Gnatzy 1977). Cercal campaniform sensilla are also important during mating because they trigger male backward
slipping (Sakai & Ootsubo 1988) and provide sensory feedback to the male on female body position during both
hooking and spermatophore transfer (Sakai & Ootsubo
1988; Snell & Killian 2000).
Suppression of Escape Behaviours
During Mating
Following mounting of the female and hooking of the
genitalia, both the male and female become relatively
rigid and immobile. All body movements cease except for
slight movements of the male abdomen, genitalia and
cerci associated with spermatophore transfer. We found
that male crickets showed a lack of responsiveness to
touch when stimulated during this stage of mating. In
addition, many males showed a significant decrease in
jumping responses to touch when stimulated immediately
following copulation. We do not think that habituation
from repetitive tactile stimulation is responsible for these
observed changes since these same males showed robust
evasive responses when repetitively stimulated in isolation, before their mating trials.
What produces the immobility and almost complete
suppression of touch-evoked responses during copulation? One possibility is that sensory feedback arising
from the position of the animals’ limbs or from the
male-to-female contact occurring during copulation plays
a role. For example, by allowing the antennae of the
cockroach P. americana to contact a mechanical barrier, an
immobile or ‘quiescent’ state can be induced in the animal
during which escape running responses normally triggered by touch or wind are suppressed (Watson & Ritzmann 1994). Interestingly, Watson & Ritzmann (1994)
found that quiescent roaches initiate antennal waving immediately prior to leaving this immobile state and regaining their responsiveness to stimulation. Similarly,
copulating A. domesticus crickets remain quiescent until
spermatophore transfer is complete and begin antennal
waving just prior to unhooking of the genitalia and female
497
498
ANIMAL BEHAVIOUR, 72, 2
dismount (personal observation). A similar immobile,
unresponsive state can be induced in the cricket G. bimaculatus. This immobile state, or thanatosis, usually lasts
2e4 min and is initiated by mechanical restraint of the
limbs (Nishino & Sakai 1996; Nishino 2004). Interestingly,
the duration of this mechanically induced thanatosis is
similar to the duration of spermatophore transfer reported
for A. domesticus mating pairs (Snell & Killian 2000).
A second possibility is that the release of neurohormones or neuromodulators within the central nervous
system following male and female antennal contact is
responsible for this widespread change in the efficacy of
escape responses. For example, in the cricket G. bimaculatus, haemolymph levels of the biogenic amine octopamine increase during courtship, and antennal contact
with a conspecific is necessary to trigger this increase
(Adamo et al. 1995). Biogenic amines may also regulate
male copulatory behaviour during mating (Matsumoto &
Sakai 2001), as well as the duration of male guarding behaviour following mating (Ureshi et al. 2002). In addition,
the escape behaviours of both crickets (Stevenson et al.
2000) and cockroachs (Goldstein & Camhi 1991; Casagrand & Ritzmann 1992; Hill & Blagburn 2001) can be
modulated by these amines.
We also found that tactile stimulation of males
15e60 min before the initiation of a mating trial negatively impacted mating success. Failures were either due
to a failure of the male to initiate courtship or because
the male showed escape responses when contacted by
the female. We suggest that repetitive tactile stimulation
of these males just before their mating trials induced the
release of neuromodulators that may have acted to inhibit
the switch from escape to mating behaviour. Mechanical
handling stress can increase haemolymph octopamine
levels in crickets (Woodring et al. 1988), locusts and cockroaches (Davenport & Evans 1984), and octopamine is
called the ‘fight or flight’ hormone of insects (reviewed
in Roeder 1999). Interestingly, when males were stimulated approximately 15 min before mating, but immediately after female contact and the initiation of courtship
(experiment 2, CS Fem pairs), this decrease in mating
success was not observed. This suggests that prior chemosensory contact with a female could act to prevent any
stress-induced enhancement of escape behaviour elicited
by repetitive tactile stimulation.
We also observed a decrease in the jumping responses of
males immediately following copulation and during the
onset of male guarding behaviour. During guarding, the
male attempts to remain in close contact with the female,
will often rest his antennae across the female’s body, and
will jerk his body and chirp aggressively in response to
any movements made by the female (reviewed in Zuk &
Simmons 1997). A decrease in male jumping responses
to touch during guarding may facilitate these interactions.
Activation of the Switch from Escape
to Mating Behaviour
We asked whether touch-evoked escape responses were
inhibited during the period between courtship initiation
and copulation. Contact of the female mouthparts, or
palps, with the male’s cerci or abdomen is needed to
initiate male backward slipping, and the female must also
mount onto the male’s back and wings. Jumping and
kicking responses to wing or cercal stimulation would thus
need to be suppressed before these events could take
place. In addition, Huber (1965) reported that isolated G.
campestris males primarily kick during tactile stimulation
of the cerci, but that both courting and guarding males respond to cercal stimulation with copulatory movements.
Accordingly, we asked whether the switch from escape
to mating behaviour is triggered during the initial period
of sex recognition, when the male and female first make
chemosensory contact.
First, our results confirmed the importance of male
courtship behaviour since all males that failed to initiate
courtship song even after 15 min of interaction with a female (No CS þ Fem pairs) failed to copulate. Male courtship song is a prerequisite for the initiation of female
receptivity and mounting behaviour in A. domesticus
(Crankshaw 1979; Nelson & Nolen 1997) as well as other
cricket species (Loher & Rence 1978; Adamo & Hoy 1994;
Balakrishnan & Pollack 1996). In addition, we found that
the touch-evoked escape responses of nonsinging males
stimulated in the presence of the female were not suppressed, indicating that these males had failed to successfully make the transition from escape to mating
behaviour.
We also found that only courting males in constant
contact with a female (CS þ Fem) would produce copulatory responses to tactile stimulation of the wings and
cerci. They also produced significantly fewer kicking and
jumping responses than did courting males stimulated
in the absence of the female (CS Fem). These results suggest that not only is male and female contact required to
initiate courtship, but that continued contact between
the male and female is necessary for mating to progress
from courtship to copulation. Our results conflict with
those of Sakai & Ootsubo (1988), who reported that courting G. bimaculatus males isolated from females would produce backward slipping and hooking movements when
mechanically stimulated. However, these researchers did
not indicate how long their mating pairs interacted before
separation and stimulation of the male. In our study, each
CS Fem male was separated from the female by an opaque divider immediately after the initiation of courtship
song by the male, whereas CS þ Fem males were in constant contact with the female during the entire stimulation period. This continuous female contact may have
provided the reinforcing stimulus needed to allow those
males to progress into copulatory behaviour. In support
of this, Matsumoto & Sakai (2000) reported that the number of courting males that responded with copulatory
movements to tactile stimulation of the cerci increased
over time from 0% (when males were stimulated immediately at the onset of courtship and following separation
from the female) to 30% (when males were stimulated after 15 min of interaction with a female).
The reinforcing stimuli experienced by the CS þ Fem
males may have been visual, chemical or tactile cues provided by the females. Hardy & Shaw (1983) found that
KILLIAN ET AL.: BEHAVIOURAL SWITCHING IN CRICKETS
upon initial antennal contact, an A. domesticus male will
respond aggressively towards a female and that continued
contact is required for sex discrimination. These authors
suggested that males require additional information other
than contact chemoreception, perhaps visual cues supplied by the sexually receptive female’s body position or
movements, to initiate courtship (Hardy & Shaw 1983).
These cues may be derived from the female antennae since
we found that female antennal ablation can negatively affect male receptivity. Similarly, sexually receptive G. bimaculatus males given the opportunity to contact and court
anaesthetized females will usually ignore them (Adamo
& Hoy 1994). However, blinded and deafened Teleogryllus
commodus males had no difficulty in courting and copulating with females (Loher & Rence 1978) and Teleogryllus
oceanicus males readily initiated courtship when allowed
to contact anaesthetized females with their antennae
(Balakrishnan & Pollack 1997).
Role of the Antennae
We found that removal of the female antennae significantly decreased mating success, whereas male antennal
ablation had little effect. For all mating trials, antennal
contact was required for sex recognition and the initiation
of courtship song and courtship behaviour by the male.
Visual cues alone were not sufficient and we found no
evidence during our experiments that males or females
responded to airborne pheromones. Similarly, male and
female antennal contact is the primary means of sex
recognition for T. commodus (Loher & Rence 1978),
G. bimaculatus (Adamo & Hoy 1994) and T. oceanicus (Balakrishnan & Pollack 1997) crickets. This contact activates
chemoreceptors on the antennae, allowing the male to
confirm the presence of a female and providing the signal
that initiates courtship behaviour (Rence & Loher 1977;
Hardy & Shaw 1983; Balakrishnan & Pollack 1997;
Tregenza & Wedell 1997).
Adamo & Hoy (1994) also reported that removal of
a male’s antennae 3 days before pairing with intact females had no effect on the mating success of G. bimaculatus crickets. In contrast, Murakami & Itoh (2003) recently
reported a significant decrease in the number of G. bimaculatus males that would court intact females 7 days after
male antennal removal, and they suggested that the longer elapsed time between antennal ablation and their behavioural tests may explain these differing results. Loher
& Rence (1978) also found that T. commodus males paired
with intact females 10 days after surgical removal of their
antennae failed to initiate courtship song and instead either ignored or acted aggressively towards females. Even
though our A. domesticus males had their antennae removed 9e20 days before behavioural trials, their courtship behaviour was not as severely affected, suggesting
that antennal inputs may be of primary importance for
sex recognition and courtship initiation for the males of
some, but not all, species of crickets.
Chemosensory contact is crucial for the initiation of
male courtship behaviour. Nevertheless, the overall success rate of mating pairs in which the males had their
antennae removed was not significantly different from
that of control pairs. Pairs that did fail to mate did so
because the antennal-ablated male failed at courtship
behaviour. Instead, many of these males chirped aggressively, jerked their bodies, kicked or ran when contacted
by a female. These behaviours were less prevalent in
control males and most, if not all, aggressive responses
ended once courtship behaviour was initiated. Similarly,
deantennated G. bimaculatus males show increased levels
of aggression towards females (Adamo & Hoy 1994).
The fact that we saw no significant effect of male
antennal ablation on mating success, or on the time or
number of contacts required to initiate courtship for
successful pairs suggests that chemosensory cues derived
from the maxillary palps could be sufficient to initiate
courtship behaviour from antennaeless males. Adamo &
Hoy (1994) reported that G. bimaculatus males and females also increase the number of contacts they make
with their palps following removal of the antennae. Klein
(1981), who described the various sensilla covering the
tips of the maxillary palps of the cricket, concluded that
most palpal sensilla function as contact chemoreceptors.
In the cricket brain, both maxillary palp afferents (Ignell
et al. 2000) and antennal afferents (Staudacher & Schildberger 1999) terminate within the deutocerebrum. This
anatomical arrangement, together with our observation
that maxillary palp information can initiate courtship behaviour in the absence of antennal inputs, suggests that
afferents from both pairs of appendages may be involved
in the activation of common neural circuits within the
brain, possibly at the level of higher integrative centres
such as the mushroom bodies (Frambach & Schurmann
2004).
Removal of the female antennae negatively affected the
ability of pairs to copulate successfully. Interestingly, more
males failed to initiate courtship behaviour when the
female lacked antennae and the male was intact than
when the male was antennal ablated and the female was
intact. In addition, for the 14 female antennal-ablated
pairs that were successful, it took more than five times as
many contacts between the male and female to initiate
male courtship, resulting in a significant increase in the
time that elapsed between the first maleefemale contact
and the initiation of courtship. In contrast, the number of
contacts and time required to initiate the courtship
behaviour of antennal-ablated males were similar to those
of intact males. These findings again suggest that visual
and/or tactile cues provided by the female antennae are
important in the expression of male courtship behaviour.
Female antennal ablation also significantly decreased
the number of pairs successfully completing male backward slipping and female mounting. About half of these
failures were because the female never became sexually
receptive and instead ignored the courting male throughout the 15-min trial. Antennal ablation also significantly
decreases the mounting responses of T. commodus (Loher
& Rence 1978) and T. oceanicus (Balakrishnan & Pollack
1997) females, however, these failures were apparently
not due to a lack of interest by the female.
The remainder of the female antennal-ablated pairs that
failed at backward slipping did so because the male would
kick, or run forward, when the female contacted his cerci
499
500
ANIMAL BEHAVIOUR, 72, 2
or abdomen. Females normally use their palps to contact
the male’s cerci and use their antennae to contact the
male’s wings and abdomen, and this contact elicits male
backward slipping and female mounting behaviour (Loher
& Rence 1978; Sakai & Ootsubo 1988). As the female
mounts, the male swings his antennae back and forth in
front and behind him, contacting the female’s head and
antennae while she holds her antennae out in front of
her (Alexander 1961; Loher & Rence 1978; Adamo &
Hoy 1994). We have also observed that when a female
cricket approaches a male from behind and contacts his
cerci with her palps, he will sometimes move forward
a few steps and then immediately resume courtship, perhaps indicating that the female was not in a proper position for mounting. Males showed an increase in such
responses when paired with a deantennated female and,
when successful mounting did occur for such pairs, the females were often misaligned. The importance of antennal
sensory feedback during mounting is also indicated by the
significantly longer time required for hooking of the genitalia by both the male and the female antennal-ablated
pairs.
In summary, we have demonstrated that male touchevoked escape behaviours are suppressed during mating.
Mating and escape are incompatible behaviours and understanding the factors controlling their production can
provide insight into the process of this behavioural
switching. The switch from escape to mating occurs
following antennal contact with a female and requires
the continued presence of the female for its full expression. The chemosensory information responsible for
triggering this switch in the male is primarily supplied
by the antennae, although information derived from
maxillary palp chemoreceptors may also be important.
However, loss of the female antennae had a significant
negative effect on both female and male receptivity and
mounting behaviour. Future work needs to focus on the
underlying neural mechanisms mediating these behavioural changes.
Acknowledgments
We thank Michael Hughes, Manager, Miami University
Statistical Consulting Center for his expert advice and
statistical assistance. We thank Rachel Orr, Christa Nagel,
Jace Perkerson and Erin Wernke for their technical
assistance in the laboratory and Kelly Pogorzelski and
Michael Sunderman for maintaining our cricket colony.
Financial support was provided by a grant from the
National Institute of Mental Health (R15 MH6060701A1) and a Miami University Committee for Faculty
Research grant.
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