Research Article

Journal of Orthoptera Research 2017, 26(2): 205-210

Listening fo male song induces female field crickets to differentially allocate

reproductive resources

JANICE J. TING!2, Kevin A, JUuDGE!3, DARRYL T. GWYNNE!

1 Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, Ontario, Canada, L5L 1C6.
2 Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks St., Toronto, ON, Canada, M5S 3B2.
3 Department of Biological Sciences, MacEwan University, 10700 104 Ave. NW, Edmonton, Alberta, Canada, T5J 482.

Corresponding author: Kevin A. Judge (judgek3 @macewan.ca)

Academic editor: Juliana Chamorro-Rengifo | Received 28 July 2017 | Accepted 17 November 2017 | Published 11 December 2017

http://zoobank.org/DDOBFA5B-1D2B-4223-AE73-74B906FCE15B

Citation: Ting JJ, Judge KA, Gwynne DT (2017) Listening to male song induces female field crickets to differentially allocate reproductive resources.
Journal of Orthoptera Research 26(2): 205-210. https://doi.org/10.3897/jor.26.19891

Abstract

Differential investment in offspring by mothers is predicted when
there is substantial variation in sire quality. Whether females invest more
resources in the offspring of high-quality mates (differential allocation,
DA) or in the offspring of low-quality mates (reproductive compensation,
RC) is not consistent in the literature and both effects can be predicted by
theoretical models. In the field cricket, Gryllus pennsylvanicus Burmeister,
1838 (Orthoptera: Gryllidae: Gryllinae), females are attracted more to call-
ing songs of high-quality males than to those of low-quality males. We
tested whether females invest reproductive resources differentially based on
perceived mate quality. We manipulated female perception of male quality
by allowing virgin females to approach a speaker broadcasting either high-
or low-quality calling song (high or low calling effort respectively), and
then mated them with a randomly chosen male that had been rendered in-
capable of calling. In the week following mating, females exposed to high-
quality calling song gained less weight, laid more embryos, and laid larger
embryos than females exposed to low-quality calling song, although only
the first of these effects was statistically significant. These results support
the DA hypothesis and suggest that females invest their reproductive output
based on a trait (calling effort) that is an honest indicator of male quality.

Key words

differential allocation, Gryllus pennsylvanicus, mate choice, maternal effects,
reproductive compensation, sexual selection

Introduction

Mate choice can occur at various stages of mating (Andersson
1994) from discrimination among pre-mating displays (e.g. Gray
1999) to post-copulation favoring of certain ejaculates (e.g. Cunning-
ham and Russell 2000). One form of post-copulatory choice is differ-
ential investment, whereby females strategically allocate reproductive
resources, such as altering the number or size of embryos, depending
on both the attractiveness of their current mate and the likelihood
of encountering another, perhaps higher quality, mate (Harris and
Uller 2009). Two alternative investment strategies have been identi-
fied where females invest more resources in the offspring of either: a)

high-quality mates — termed differential allocation (DA) (Williams
1966, Burley 1986, Sheldon 2000) or b) low-quality mates - termed
reproductive compensation (RC) (Gowaty et al. 2003, Gowaty 2008).
Modelling of differential investment by females indicates that DA
occurs under a wider range of conditions, suggesting that it should
be more common than RC in nature (Harris and Uller 2009). To
date, the empirical literature is inconclusive as to which strategy is
more prevalent (reviewed in Harris and Uller 2009). This inconsist-
ency can perhaps be explained by the fact that the extent and type of
differential investment is also dependent on the state of the female
(i.e. energetic resources, age) and timing during the breeding season
(Harris and Uller 2009), as well as what metric is used to measure
differential investment (i.e. clutch or offspring size, Kindsvater and
Alonzo 2014).

Successful demonstration of differential investment requires
careful manipulative experiments (Sheldon 2000) where the male
trait that is subject to female mating preference is experimentally
manipulated and the reproductive output of females mated to ma-
nipulated males is measured. This kind of manipulative experi-
ment has the advantage of controlling for confounding male traits
that may directly cause changes to females’ reproductive output
(e.g. material benefits). For example, male attractiveness in zebra
finches (Taeniopygia guttata [Vieillot, 1817]) was manipulated by
adding leg bands with colors preferred by females. In response
to this manipulation, mothers invested more mass in eggs sired
by attractive males than in eggs sired by unattractive males (Gil-
bert et al. 2006). Mated female canaries (Serinus canaria |Linnaeus,
1758]) were exposed to recordings of either attractive or unattrac-
tive male songs before they laid their first clutch, and then the
opposite song type before laying their second clutch. Females allo-
cated more testosterone (an important egg resource) to eggs when
exposed to attractive male songs (Gil et al. 2004). In another bird,
the North African houbara (Chlamydotis undulata [Jacquin, 1784]),
artificially inseminated females visually stimulated by highly dis-
playing males had higher hatching success, and allocated more
androgens to their eggs leading to increased growth rates in chicks
(Loyau and Lacroix 2010).

JOURNAL OF ORTHOPTERA RESEARCH 2017, 26(2)

206

The study of differential investment by females has been dom-
inated with avian examples (reviewed in Horvathova et al. 2012),
however there are a few studies on other animals (e.g. water frog:
Reyer et al. 1999, dung beetle: Kotiaho et al. 2003, swordtail fish:
Kindsvater et al. 2013). Using a quantitative genetic approach,
Head et al. (2006) detected an association between male attrac-
tiveness and female reproductive output in the domestic cricket,
Acheta domesticus (Linnaeus, 1758). Larger females were found to
lay more embryos when mated to attractive (large) males (Head et
al. 2006). However, this result should be considered, at best, weak
evidence for DA because the trait preferred by females (male size)
was hot manipulated and thus likely covaries with other aspects of
the male phenotype that affect female fitness (e.g. seminal prod-
ucts, Wagner and Harper 2003). Here, we were interested in con-
ducting a strong test of maternal differential investment (Sheldon
2000) by examining whether experimental allocation of a natural,
precopulatory sexual signal could elicit differential investment by
females of acommon and widespread insect.

Male field crickets (Gryllidae: Gryllinae) produce both a long-
range calling song used to attract females from a distance, and a
short-range courtship song produced just prior to copulation (Al-
exander 1961). Precopulatory choice of male song has been exten-
sively studied in gryllids (e.g. Gray 1997, Hunt et al. 2004, Judge et
al. 2014), and females have been found to base their mate choice
decisions on a range of song characteristics. For example, female
field crickets are attracted to greater calling effort (e.g. Cade and
Cade 1992, Hunt et al. 2004, Judge et al. 2014). However, to date,
no study has demonstrated postcopulatory choice of male song
through differential investment.

In this study, we manipulated apparent mate quality as per-
ceived by female fall field crickets, Gryllus pennsylvanicus Burmeister,
1838, by exposing virgin females to playbacks of either high or low
effort calling songs, since greater calling effort is both preferred by
females (Judge et al. 2014) and an indicator of male quality (Judge
et al. 2008). We measured the reproductive output (i.e. female
mass change, number and size of embryos, and female lifespan) of
experimental females to determine whether female G. pennsylvani-
cus differentially invest and if so, whether they invest more in the
offspring of high-quality mates (DA) or low-quality mates (RC).

Materials and methods

Experimental animals.—Late-instar G. pennsylvanicus nymphs were
individually housed in plastic containers (9 cm diameter, 8 cm
high) with several pieces of rabbit chow (Martin’s Little Friends
Rabbit Food) for food, a cotton-plugged microfuge tube filled
with water for moisture, and a small piece of cardboard egg car-
ton for shelter. We measured body weight to the nearest milligram
using a Mettler AE 50 balance on both the day following their
moult to adulthood and the day prior to testing — the latter being
used to match experimental pairs. The experiment had a paired
design such that pairs of females, experiencing either the high- or
low-effort song (see below), were matched for weight (within 5%)
and were mated to one of a pair of males that were also matched
for weight. In this way, we minimized variation in female repro-
ductive output due to differences in female and male body size
(which is linked to attractiveness, e.g. Simmons 1987). Female
size can also affect embryo size and offspring size (e.g. burying
beetles, Steiger 2013).

Manipulation of male attractiveness.—Calling songs were record-
ed from wild males in Mississauga, Ontario (43°32’50.51“N,

J.J. TING, K.A. JUDGE AND D.T. GWYNNE

79°39'37.80"W) in August and September of 2003. Songs were
recorded using an Audio-Technica shotgun microphone con-
nected to a Tascam DA-P1 digital audio tape recorder. Recordings
were transferred to a computer, and saved as 48 kHz, 16-bit mono
wav-files using CoolEdit 2000. Attractive and unattractive calling
songs were the same as those used in Judge et al. (2014). Briefly, a
single representative chirp from each song recording was used to
create both an attractive and unattractive calling song model for
each male, where song attractiveness was defined by the percent-
age of time filled with chirps as was found previously to be both
preferred by females (Judge et al. 2014) and condition-dependent
Judge et al. 2008). Attractive calling songs were 90% chirp-filled
while unattractive calling songs were 10% chirp-filled (based on
a standardized chirp period of 0.432 s and a time frame of 13 s).
Thus, every 13 s a female hearing an attractive calling song would
experience one bout of calling song consisting of 27 chirps, where-
as a female hearing an unattractive calling song would experience
one 3-chirp bout. These values for calling effort are within the
range measured for males of this species (0-100%, unpublished
data). Our paired experimental design also ensured that each pair
of females experienced calling song models constructed from one
recording. Thus, one female was exposed to the attractive version
(high-quality song treatment: HT) while the other female was ex-
posed to the unattractive version (low-quality song treatment: LT).

Phonotaxis trials. —We allowed sexually mature (minimum of 10
days post adult eclosion; KAJ pers. obs.), virgin females to approach
speakers broadcasting either attractive (HT) or unattractive (LT)
calling song. We conducted no-choice phonotaxis trials in a sound-
attenuating room to minimize environmental noise and under red
light as crickets are nocturnal. The phonotaxis arena we used was
identical to the one used by Judge et al. (2014). Briefly, the arena
consisted of a plastic Rubbermaid bin (85 cm long, 47.5 cm wide
and 12 cm high) with two 7.5 cm-diameter circles cut into the floor
that were 10 cm from each end and 50 cm apart. In the circular
holes, a short plastic tube topped with metal screen was raised 1 cm
above the floor. Sand was added to the arena so it was flush with
the metal screen. The speakers (Apple in-ear headphones, model
MA662G/A) were placed 0.5 cm below the center of each of the
metal screens. Peak sound pressure level was an average (+ SE) of
72.4 dB (+ 0.1 dB) at the centre of the arena (Judge et al. 2014).
We randomly assigned one of the two speakers to broadcast the
calling song model. Before the start of each trial each female was
enclosed at the centre of the arena, equidistant from the two speak-
ers, under a plastic container with a piece of cardboard as shelter.
The calling song model was broadcast during a two-minute accli-
mation period, after which we carefully raised the plastic container.
Thus, the female had an option of remaining sheltered until she
commenced phonotaxis. Females were allowed a maximum of 20
minutes to choose the broadcasting speaker. A choice was recorded
when the female’s body paused (=5 seconds) over the metal screen
above the broadcasting speaker. Following each trail, we eliminated
any pheromone cues left by females by mixing the sand, and wiping
down the choice zones and the sides of the arena with 95% ethanol.

Mating.—After a female chose the broadcasting speaker, she was
corralled on top of the speaker inside a plastic tube (7.5 cm di-
ameter, 8 cm high). To re-acclimate the female, following this dis-
ruption, we allowed a further two-minute broadcast of the same
calling song played during their phonotaxis trial. We then stopped
the calling song and added an experimentally silenced male (see
below) to the cylinder. Then we exposed all females to the same

JOURNAL OF ORTHOPTERA RESEARCH 2017, 26(2)

J.J. TING, K.A. JUDGE AND D.T. GWYNNE

recording of a courtship song to induce the female to mate. We
played the courtship song as soon as we observed the silenced
male raising his truncated singing forewings. All males were iso-
lated from the calling songs broadcast during the trials to reduce
any possible effects the songs may have had on the male.

Prior to mating, males were experimentally silenced by trim-
ming off the ends of the forewings with a pair of micro-scissors
thereby removing the stridulatory apparatus necessary in song
production (Walker and Carlysle 1975). Our wing trimming
protocol controlled for effects of the wing alteration on female
reproduction. For example, male attractiveness was manipulated
in male beetles Tribolium castaneum (Herbst, 1797) by truncating
their middle legs to reduce female perception of courtship leg-
rubbing rate, which resulted in a reduced oviposition rate by the
mated female (Edvardsson and Arnqvist 2005). This effect could
have been a response to the wounding trauma, or the truncated leg
itself. With our manipulated crickets, all males raised and moved
their truncated wings when courting females, and more impor-
tantly, we exposed all females, both in attractive and unattractive
treatments, to these experimentally silenced males.

Following spermatophore transfer, we restrained females for
an hour, on the surface of a petri dish with a small piece of plastic
wrap weighed down by a plastic ring. By restraining the female,
we controlled for spermatophore attachment duration by prevent-
ing the female from eating or detaching the spermatophore, as
females can control paternity through the removal of the spermat-
ophore (Sakaluk and Eggert 1996).

Measurement of female reproductive output.—Following copulation,
we provided females with moist gauze as an oviposition substrate,
food, water, and shelter. At one-week intervals following mating,
we weighed each female and collected all embryos laid during the
week. We counted the embryos laid by each female and then sub-
sampled a maximum of 10 embryos, which were then measured us-
ing ImageJ (Version 1.37). Embryo morphological measurements
collected were: length, perimeter and area. Thus, for every week
following the experiment until death we measured each female’s
weight change, number of embryos laid, and embryo morphology.

Statistical analysis. -Embryo measurements (length, perimeter and
area) were reduced to a single measure of overall embryo size us-
ing a principal component analysis conducted in SPSS (Version
23). The mean value of all the embryos measured in each clutch
(range 1 to 10 embryos measured) were included in the PCA,
meaning that each clutch was represented by one length, perim-
eter and area measurement. Prior to statistical analysis, all data
were tested for normality using Kolmogorov-Smirnov normality
tests. As most dependent variables failed to satisfy the parametric
assumption of normality, and sample size was reduced because
several females failed to lay embryos, we chose to use randomiza-
tion procedures to test our hypotheses. Specifically, we used per-
mutation tests (Legendre and Legendre 2012) to generate a null
distribution of effect sizes by randomly shuffling the dependent
variable amongst treatment groups and calculating an effect size
based on each new randomization. Repetition of this procedure
(10000 times in our case) generates a distribution of effect sizes
based on the sample data. Hypothesis testing proceeds by calcu-
lating the proportion of randomly-generated effect sizes that are
greater than or equal to the measured effect size — this proportion
is equivalent to a p-value (Legendre and Legendre 2012). In addi-
tion, we generated 95% confidence intervals around each of our
effect sizes using bootstrapping. Permutation tests and bootstrap-

207

ping were conducted using the PopTools (Version 3.2.5) add-in
for Microsoft Excel (Hood 2011).

Results

We assessed 31 pairs of females for their latency to respond to
a male’s calling song (either high or low-quality), and then their
subsequent reproductive output. Females in the two experimen-
tal groups (HT or LT) did not differ in weight before the treat-
ment application (mean difference [LT - HT], 95% CI: 0.3 mg,
-5.0-5.4 mg; N = 31 pairs, paired permutation test p = 0.918). All
62 females responded to the speaker broadcasting the calling song
within the 20-minute time frame. Females responded more quick-
ly to high- than low-quality calling songs (mean difference [LT -
HT], 95% CI: 204.5 s, 44.8-368.7 s, N = 31 pairs, paired permuta-
tion test p = 0.023; Fig. 1). Experimentally muted males courted LT
females faster than HT females, although this difference was not
statistically significant (mean difference [LT - HT], 95% CI: -40.4
s, -103.8-22.2 s, N = 31 pairs, paired permutation test p = 0.224).
Two females failed to mate during the allotted 20-minute time
period so their latency to mount was set to the maximum. Females
of the two treatments (LT and HT), did not differ in their latency
to mount the male (mean difference [LT - HT], 95% CI: 58.6 s,
-130.5-249.7 s, N = 31 pairs, paired permutation test p = 0.546).

Following mating, eight individual females failed to lay em-
bryos during their lifetime. There was no difference between fe-
males of either treatment in their likelihood of failing to produce
embryos (LT: 5/29, HT: 3/29; Chi-Squared with continuity cor-
rection: y2 = 0.144, p = 0.704). Because one female's failure to
lay embryos would eliminate both females from a paired analysis,
we decided to include all females who laid embryos at least once
and conduct unpaired statistical analyses to maximize our sample
size. Furthermore, one female died midway through the first week
of embryo laying, which prevented us from measuring her weight
change and so we eliminated her from subsequent analyses giving
us a final sample size of 51 females (LT: n=25, HT: n=26).

To test for an effect of song exposure on female reproductive
output, we compared the embryo laying rate, mass change, and
embryo size of LT and HT females during: 1) the first week of em-
bryo deposition (Week 1) — the most biologically relevant time pe-
riod because few gryllids live beyond 25 days in the wild (Murray
and Cade 1995), and 2) the weeks following the first week after
treatment until death (Post Week 1). For the Post Week 1 period
we calculated: 1) embryo laying rate (total number of embryos
laid divided by the number of days alive post week 1), 2) female
weight change (difference in weight between the last weight meas-
urement and the female’s weight at the end of week 1), and 3)
female lifespan. Given that not all females laid embryos in the
first week and some females did not lay embryos after week one,
the analyses of embryo size have smaller sample sizes (Week 1: 18
LT, 20 HT; Post Week 1: 21 LT, 25 HT). Finally, to adjust for infla-
tion of Type I error rates due to multiple testing, we adjusted our
threshold for statistical significance using the sequential Bonfer-
roni method (Holm 1979).

The principal components analysis of embryo length, area
(square root) and perimeter resulted in one principal component
with an eigenvalue over 1 that explained over 91% of the variation
in embryo measurements (Table 1). We therefore use PC1 as an
index of embryo size in all analyses.

Females exposed to high-quality song (HT) gained less weight,
laid larger embryos and laid more embryos during the first week
after mating than females exposed to low-quality song (LT). Only

JOURNAL OF ORTHOPTERA RESEARCH 2017, 26(2)

208

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High
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Fig. 1. Mean (+SE) latency of females to choose the speaker broad-
casting either low- or high-quality calling song.

100

bt 80

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ev 60

Cc

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Week 1 Post Week 1

Fig. 2. Mean (+SE) change in mass during: the first week following
treatment (Week 1), and the subsequent weeks following treat-
ment (Post Week 1) of females who experienced either low- (grey
symbols) or high- (black symbols) quality calling song.

Table 1. Summary of the results of the principal components anal-
ysis of the three embryo measures. Values are the factor loadings
and percent variance explained by principal component one.

Embryo Measure PCl1
Area (square root) 0.890
Perimeter Ui935
Length 0.918
% Variance Explained 91.4

the effect on weight change was found to be statistically significant
(mean difference [LT - HT], 95% CI: weight change = 57.9 mg,
20.4-96.9 mg, N = 51, permutation test p = 0.014, Fig. 2; embryo
size (PC1) = -0.597, -1.346-0.126, N = 38, permutation test p =
0.265, Fig. 3; embryo laying rate = -3.1 embryos/day, -7.3-0.8 em-
bryos/day, N = 51, permutation test p = 0.163, Fig. 4). However,
after the first week following either the low- or high-quality calling

J.J. TING, K.A. JUDGE AND D.T. GWYNNE

1.25

1.00

0.75

0.50

0.25

0.00

Mean Embryo Size (PC1)

t

Post Week 1

-0.25

-0.50
Week 1

Fig. 3. Mean (+SE) size of embryos laid during: the first week fol-
lowing treatment (Week 1), and the subsequent weeks following
treatment (Post Week 1) of females who experienced either low-
(grey symbols) or high- (black symbols) quality calling song.

= 10
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Week 1 Post Week 1

Fig. 4. Mean (+SE) embryo laying rate during: the first week fol-
lowing treatment (Week 1), and the subsequent weeks following
treatment (Post Week 1) of females who experienced either low-
(grey symbols) or high- (black symbols) quality calling song.

song treatment, females did not differ in the amount of weight
change, embryo size, embryo laying rate, or lifespan (mean differ-
ence [LT - HT], 95% CI: weight change = 2.70 mg, -45.3-48.0 mg,
N = 49, permutation test p = 0.912, Fig. 2; embryo size = -0.1522,
-0.6153-0.2972, N = 49, permutation test p = 0.527, Fig. 3; em-
bryo laying rate = -0.6 embryos/day, -2.4—1.5 embryos/day, N = 51,
permutation test p = 0.596, Fig. 4; lifespan = -0.1 days, -6.9-6.5
days, N = 51, permutation test p = 0.981).

Discussion

Female G. pennsylvanicus preferred (responded more quickly to)
high-quality rather than low-quality calling songs (Fig. 1, see also
Judge et al. 2014). In the first week following exposure to a high-
quality calling song and mating with a muted male, HT females
gained less weight (Fig. 2), and there was a trend toward them lay-

JOURNAL OF ORTHOPTERA RESEARCH 2017, 26(2)

J.J. TING, K.A. JUDGE AND D.T. GWYNNE

ing larger embryos (Fig. 3) and more embryos (Fig. 4) compared
to LT females exposed to a low-quality calling song and mated to
a muted male. We did not detect an effect of our manipulation of
perceived mate attraction on any of the measures of female repro-
ductive investment nor female lifespan after the first week following
song exposure (Figs 2-4). Although we cannot conclusively say that
female G. pennsylvanicus differentially invest reproductive resourc-
es — because embryo number and size were not statistically differ-
ent between treatments — our results suggest that females follow
a strategy of differential allocation (DA) rather than reproductive
compensation (RC) since HT females gained less weight than LT fe-
males and the number of embryos laid by females is correlated with
their weight change in the first week after song exposure (Spearman
rank correlation: rho = -0.301, N = 48, p = 0.038).

Although modeling suggests that DA will be more prevalent
than RC in nature (Harris and Uller 2009), to date, the empiri-
cal evidence is inconclusive (e.g. Arnold et al. 2016, reviewed in
Harris and Uller 2009, Horvathova et al. 2012). Our finding, that
female G. pennsylvanicus display some evidence of DA based on
male calling song effort, adds both empirical support to the theo-
ry and strengthens earlier evidence of DA in field crickets (Head et
al. 2006). In Acheta domesticus, larger females mated to attractive
(larger) males laid more embryos than females mated to unattrac-
tive males (Head et al. 2006). However, increased oviposition rate
by female A. domesticus may have been caused by seminal prod-
ucts, if these substances covaried with male attractiveness and/
or size (e.g. Wagner and Harper 2003). Our experimental design
ruled out effects of male seminal products on oviposition rate
(e.g. Stanley-Samuelson et al. 1987) because we manipulated only
male attractiveness as recommended by Sheldon (2000). Thus,
the change in female weight could only have been a response to
our experimental manipulation and not to other aspects of male
phenotype such as seminal products or cuticular hydrocarbons.

Female body size is positively related to reproductive output
in G. pennsylvanicus crickets (Carriére and Roff 1995). HT females
in our experiment gained less weight (Fig. 2), laid larger embryos
(Fig. 3) and laid more embryos (Fig. 4) than LT females. Although
only the effect on weight change was statistically significant, we
suggest that differences in both the number and size of embryos
laid contribute to the weight change effect since weight change
was correlated with embryos laid in the first week following mat-
ing. An alternative, less parsimonious, explanation is that HT fe-
males did not invest more into offspring production, but instead
simply decreased food intake. Although we did not measure food
intake after mating and provided food ad lib, we do not think this
is likely as the full explanation because it: a) does not account
for the direction of effect on offspring production (both size and
number), and b) does not seem adaptive. However, caution in in-
terpretation is warranted and future work should seek to replicate
these findings as well as investigate the effects of DA on future
reproduction and offspring fitness.

We were unable to detect any statistically significant differences
in oviposition rate and embryo morphology. It is possible that fe-
male G. pennsylvanicus use song quality to differentially invest in
other fitness traits such as embryo weight, hatching success, nym-
phal hatching size, or sex ratio. Perhaps female crickets use their en-
ergy reserves to allocate a hormone or a chemical that increases off-
spring fitness, like that of birds, that was not explored in this study.
For example, female zebra finches paired with attractive males (Gil
et al. 1999) and canaries exposed to an attractive male song (Gil
et al. 2004), invest more yolk T (testosterone), an androgen that
may have effects on hatching success, offspring growth rate, and

209

immune function (reviewed in Groothuis et al. 2005). And in Chla-
mydotis undulata, females highly stimulated by male visual displays
did not lay more eggs, but had higher fertilization and hatching
success and allocated more maternal androgens to their eggs, lead-
ing to increased circulating testosterone and increased growth rates
in chicks (Loyau and Lacroix 2010). Examining the performance,
both survival and reproduction, of offspring laid by female G. penn-
sylvanicus exposed to high and low-quality calling songs will help
elucidate the fitness consequences of differential allocation.

Acknowledgements

Thank you to Glenn Morris for his advice on playback experi-
ments and all things acoustic, Mark Fitzpatrick for his valuable
insight and knowledge, as well as Jonathan Schneider for all his
support and helpful suggestions. This research was funded by a
Discovery Grant from the Natural Sciences and Engineering Re-
search Council (NSERC) to DTG and an NSERC Post-Graduate
Scholarship to KAJ.

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