ANIMAL BEHAVIOUR, 2002, 64, 881–886
doi:10.1006/anbe.2002.2004, available online at http://www.ScienceDirect.com
Female–offspring communication in a Taiwanese tree frog,
Chirixalus eiffingeri (Anura: Rhacophoridae)
YEONG-CHOY KAM & HUI-WEN YANG
Department of Biology, National Changhua University of Education
((Received 12 October 2001; initial acceptance 3 January 2002;
final acceptance 14 May 2002; MS. number: 7096) )
We assessed the roles of visual and olfactory cues in female–tadpole communication in Chirixalus
eiffingeri. The mean cumulative time that at least one tadpole was active or begged for food was
significantly longer when a female C. eiffingeri was present than when a plastic frog was introduced and
when no frog was present. Tadpoles did not respond visually to a female frog physically separated from
them by transparent Plexiglas. However, tadpoles were more active in water conditioned by female frogs
than in unconditioned water. Tadpole activity was further elevated by water conditioned by a female frog
and tadpoles. Tadpoles were more active in water conditioned by male frogs than in unconditioned
water, but water conditioned by a male frog and tadpoles did not further elevate tadpole activity. Thus,
water conditioned by adults of either sex contains substances that increase tadpole activity, but only
females show a synergistic effect with conditioning by tadpoles.
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2002 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour
Oviposition by frogs in phytotelmata, unique aquatic
microhabitats, is probably an evolutionary adaptation for
avoiding the predators that inhabit larger aquatic habitats
(Duellman & Trueb 1986; Lannoo et al. 1987; Summers
1990; Caldwell 1993; Jungfer 1996; Kam et al. 1996).
Maternal provisioning of eggs to feed arboreal tadpoles
probably evolved in response to food scarcity in
phytotelmata (Wassersug et al. 1981). Laboratory and
field studies have revealed that egg provisioning may be
biparental or uniparental, and that female–tadpole communication is particularly important in uniparental care.
In biparental care, the female lays eggs to feed the
tadpoles in the presence of a male frog. During provisioning, male and female frogs return to the hole, engage in
courtship behaviour, and lay fertilized or unfertilized eggs
in the pool (Caldwell & deOliveira 1999). Fertilized eggs
that are not consumed by the tadpoles will later hatch
and become the next cohort of tadpoles. Biparental
care occurs in Osteopilus brunneus (Thompson 1996),
Osteocephalus oophagous (Jungfer & Weygoldt 1999), and
Dendrobates vanzolinii (Caldwell & deOliveira 1999).
In uniparental care, the female frog lays unfertilized
eggs to feed the tadpoles in the absence of male frogs.
Interactions between a female frog and tadpoles seem
to signal or induce the female to lay trophic eggs
Correspondence and present address: Y.-C. Kam, Department of
Biology, Tunghai University, Taichung 407, Taiwan, R.O.C. (email:
[email protected]). H.-W. Yang is at the Department of
Biology, National Changhua University of Education, Changhua
50058, Taiwan, R.O.C.
0003–3472/02/$35.00/0
for the tadpoles. Chirixalus eiffingeri tadpoles, which are
obligatorily oophagous, are fed intermittently by females
that lay unfertilized trophic eggs (Kam et al. 1996). When
a female frog returns to the nest, tadpoles immediately
aggregate around her. Each tadpole stiffens its tail and
begins vibrating vigorously, while nipping at the skin
around her cloaca and thighs (Ueda 1986). The female
begins to lay trophic eggs, a few at a time, although no
males are present. As soon as the eggs are laid, the
tadpoles bite them and suck out the yolk (Ueda 1986).
Similar ‘egg-begging’ behaviour has also been reported
in a dendrobatid frog (Dendrobates pumilio) and two
hylids (Anotheca spinosa and O. brunneus) from the New
World tropics (Weygoldt 1980; Jungfer 1996; Thompson
1996).
To date, studies of female–tadpole communication
have been mostly observational, and the communication
between female frogs and tadpoles has not been studied
experimentally. Jungfer (1996) studied the brooding
behaviour of A. spinosa and showed that tactile stimulation by the tadpoles was essential for inducing female
frogs to lay trophic eggs. Anotheca spinosa and C. eiffingeri
tadpoles nip the female’s skin throughout of a feeding
event. This behaviour is fastest and most vigorous
moments before eggs are deposited in the pool (Jungfer
1996; Y.-C. Kam, unpublished data). Why do tadpoles
continuously nip the skin of female frogs? If tactile
stimulation of the female frog by tadpoles is necessary to
induce her to lay eggs, she might communicate with the
tadpoles to encourage their nipping.
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2002 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour
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ANIMAL BEHAVIOUR, 64, 6
We investigated experimentally female–tadpole communication in C. eiffingeri. We assessed in particular the
possible role of visual and olfactory cues in this communication and the properties of the chemical cues.
Chirixalus eiffingeri is a small frog (snout–vent length
ca. 30–40 mm), endemic to Taiwan and two adjacent
small islands, Iriomote and Ishigaki (Kuramoto 1973;
Ueda 1986). During the breeding season (February–
August), male frogs call from bamboo stumps. Frequently,
more than one male frog occupies a bamboo stump, and
they compete for females. Female frogs deposit fertilized
eggs above the waterline on the inner walls of tree holes
or bamboo stumps (Kuramoto 1973; Kam et al. 1998a).
Upon hatching, tadpoles drop into the pool of water
where they grow and develop until metamorphosis. Male
frogs moisten the eggs during the embryonic stage, but
leave the stumps after the embryos have hatched. Female
frogs visit and feed tadpoles at night at intervals of about
8 days (Kam et al. 2000). The length of the larval period,
from hatching to metamorphosis, is 50–60 days (Kam
et al. 1998b). Tadpoles are not cannibalistic, but they
sometimes scavenge the remains of dead siblings. The
effects of scavenging on the growth and development of
tadpoles are negligible (Kam et al. 1996, 1998b, 2000).
GENERAL METHODS
Study Animals
In April 1999, we collected 10 pairs of C. eiffingeri in
amplexus from the bamboo forests of Chitou, Nantou
County, and transported them to our laboratory in
Changhua. Each pair of frogs was maintained in a glasssided terrarium (4227 cm and 30 cm high) containing a
layer of moist soil, plants, and a bamboo stump half filled
with water. The frogs were fed house flies ad libitum. The
terraria were placed in an animal room at 20–22C and
a 12:12 h photoperiod. All frogs successfully deposited
fertilized eggs in the bamboo stumps in the terraria
(between May and September). Female frogs provisioned
eggs to feed tadpoles, as evidenced by the growth of
tadpoles.
We collected about 340 tadpoles from bamboo stumps
in the forest. Only tadpoles at Gosner stages 26–29
(Gosner 1960) were used. Each tadpole was used once in
each experiment. Each female frog was used only once in
each experiment, but owing to a shortage of female frogs
during the study period, each female was used in more
than one experiment.
At the end of the experiments, all frogs were returned
and released in the bamboo forest in Chitou. At the
end of each experiment, we transported the tadpoles to
Chitou and put them in bamboo stumps that already
contained tadpoles. Because female C. eiffingeri feed both
kin and nonkin (Kam et al. 2000), all tadpoles in the
bamboo stumps were fed and grew normally, eventually
reaching metamorphosis (Kam et al. 1998a; Chen et al.
2001). We fed tadpoles with chicken egg yolk once every
4 days until they were returned to the wild. An earlier
study showed that chicken egg yolk is a good substitute
for C. eiffingeri eggs. Furthermore, tadpoles that were fed
once every 4 days grew as well as tadpoles that were fed
by a female frog (Liang et al. 2002). The study was
conducted in accordance with the legal requirements of
the National Science Council.
Statistics
The data were analysed with nonparametric statistics
(SAS Institute Inc. 1996). The Mann–Whitney test or
Kruskal–Wallis test was used to evaluate tadpole
responses when samples were independent, and the
Wilcoxon test or Friedman test for matched samples. If,
and only if, the overall effect was significant (Kruskal–
Wallis test or Friedman test), we then performed multiple
comparisons (Mann–Whitney test or Wilcoxon test,
respectively) to determine which pairs of treatments were
significantly different. For all variables, meansSD are
reported unless otherwise noted and two-tailed tests were
used.
EXPERIMENT 1:
PRESENCE OF FEMALE
Methods
We assessed tadpole activity under three conditions: (1)
when a female frog was present; (2) when a plastic frog of
similar size was present; and (3) when a frog was not
present. For each trial, we placed 10 tadpoles in a plastic
container (99 cm and 7 cm high) in distilled water
1.5 cm deep. We placed a female or plastic frog in the
container and lowered a styrofoam lid to 1 cm above
the water to prevent the female escaping. After allowing
30 s for the animals to settle down, we videotaped the
tadpoles through the bottom for 5 min. Using the same
procedures, we also videotaped tadpoles in the container
for 5 min when no frogs were added. Each group of 10
tadpoles was subjected to each treatment only once. The
treatment order for each group of tadpoles was assigned
randomly. We conducted eight trials for each treatment.
We assessed tadpole responses by measuring two variables: (1) the cumulative time at least one tadpole was
active; and (2) the cumulative time at least one tadpole
begged for eggs over a 5-min period. Inactivity was
defined as the absence of forward movement. A tadpole
moving its tail slightly without causing forward body
movement was considered inactive. A tadpole engaged
in egg-begging behaviour stiffened its tail and vibrated
vigorously, often nipping the skin of any female frog that
was present. Egg begging was conspicuous and easy to
differentiate from the undulating tail movements typical
of tadpoles when females were absent.
Results
The mean cumulative time at least one tadpole was
active varied significantly between treatments (Friedman
test: 22 =13.12, P<0.01; Fig. 1). Tadpoles were most active
when a female frog was present and significantly more
active than tadpoles in the container with a plastic frog or
no frog (Wilcoxon: test: T=3.37, N=8, P=0.005 in both
KAM & YANG: ANURAN FEMALE–OFFSPRING COMMUNICATION
300
Active
Begging
Mean cumulative time (s)
250
200
150
the female from the side and from below. After allowing
30 s for the animals to settle, we videotaped the tadpoles
through the bottom of the large container for 5 min. The
control treatment used the same set-up but there was no
female frog in the small container. Each group of 10
tadpoles was subjected to each treatment once. For each
group of tadpoles, the treatment order was assigned
randomly. We conducted eight trials of each treatment.
We counted the cumulative time at least one tadpole was
active during a 5-min period using the criteria described
in experiment 1.
Olfactory cues
100
50
0
Female frog
Plastic frog
None
Treatment
Figure 1. The mean cumulative time at least one tadpole was active
or begged for eggs in a 5-min period when a female frog, a plastic
frog, or no frogs were present. Values are means±SD. N=8
replicates.
cases). The activity of tadpoles in the treatment with a
plastic frog and without a frog did not differ significantly
(Wilcoxon test; T=0.42, N=8, P=0.72).
The mean cumulative time at least one tadpole was
begging also varied between treatments (Fig. 1), with
tadpoles begging more when a female was present than
when a plastic frog was present (Wilcoxon test: T=3.37,
N=8, P=0.0009). Tadpoles did not beg in the no-frog
treatment. In the treatment where the female frog was
present, the mean cumulative time tadpoles were active
was significantly correlated with the time tadpoles spent
begging (Spearman rank correlation: rS =0.977, N=8,
P=0.0001). In all eight trials with female frogs, tadpoles
actively nipped the females. Some female frogs sat quietly
as tadpoles nipped them, but others moved around. Some
females appeared reluctant to be nipped by the tadpoles
and used their hindlegs to push tadpoles away. These
females tried to leave the water, but could not because of
the lid. None of the female frogs laid unfertilized eggs in
response to the begging of the tadpoles.
EXPERIMENT 2:
VISUAL AND CHEMICAL CUES
Methods
Visual cues
We placed a female frog in a small, transparent,
Plexiglas container (99 cm and 7 cm high) and lowered
a perforated styrofoam lid to 1 cm above the water to
prevent her escaping. The container was half submerged
and suspended in a larger, transparent, Plexiglas container (1515 cm and 10 cm high) containing distilled
water and 10 tadpoles. This set-up allowed tadpoles to see
To assess the olfactory response of tadpoles, we used
distilled water conditioned by female frogs (treatment
group) and distilled water (control group). We used distilled water because it was more comparable to natural
conditions in that the water in nests (tree holes or
bamboo stumps) is derived primarily from rain. Prior to
the experiment, one female frog was immersed for 4 h in
each of 10 beakers containing 50 ml of distilled water.
The conditioned water from each beaker was filtered and
then the water from the 10 beakers was pooled. In each
trial, we poured 50 ml of conditioned water into plastic
cup A and 50 ml of distilled water into plastic cup B. A
tadpole was placed in each cup, and videotaped for 5 min,
after allowing 30 s for settling. After videotaping, we
placed the tadpoles in separate beakers containing distilled water for a 1–min rest. Then, the tadpole that had
been in cup A was put in cup B and the tadpole from cup
B was placed in cup A. After allowing 30 s for settling, we
videotaped both tadpoles for 5 min. This design minimized bias caused by individual differences in activity.
However, by doing so, we subjected the second tadpole to
distilled water that was conditioned briefly by the first
tadpole. Similarly, the second tadpole was subjected to
female-conditioned water that was conditioned briefly by
the first tadpole. We ran statistical tests and found that
the presence of the first tadpole in distilled water or
female-conditioned water had no effect on the activity
level of the second tadpole in the subsequent experiments (Mann–Whitney test: U=137, N1 =N=15, NS;
U=127, N1 =N2 =15, NS, respectively). We therefore averaged the active time of two tadpoles in each condition
to give a measure of tadpole response. There were 15
measurements (trials) of tadpole response of each treatment. We assessed tadpole response by measuring the
cumulative time each tadpole was active.
Results
Tadpoles did not respond to the female frog in the
visual experiment. They moved little whether a female
frog was present (11.27.3 s, N=8) or absent (10.8
7.0 s, N=8). The mean cumulative active time did not
differ significantly between treatments (Wilcoxon test:
T= 0.11, N=8, P=0.958). During videotaping, some
female frogs moved around and stretched. The tadpoles
did not respond to the female’s movements and remained
immobile most of the time.
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ANIMAL BEHAVIOUR, 64, 6
Table 1. The activity levels (time spent active, s) of tadpoles in water
conditioned by adult frogs (females or males) alone, adult frogs
(females or males) and tadpoles, and tadpoles alone
Adult frogs
alone
Adult frogs
and tadpoles
Tadpoles
alone
Females
22.3±7.5
(7.0±2.7)
50.4±24.8
(8.0±4.5)
6.2±5.0
(4.0±4.2)
Males
18.2±5.9
(6.0±5.9)
21.7±17.1
(9.0±6.1)
Adults
The values in parentheses are the activity levels of tadpoles in
unconditioned, distilled water. Values are reported as mean±SD,
N=15 replicates.
In the olfactory experiment, tadpoles in water conditioned by female frogs moved significantly more than
those in distilled water (Wilcoxon test: T=4.62, N=15,
P=0.0001; Table 1).
EXPERIMENT 3:
CHEMICAL CUES
Methods
Sex-specific chemical cues
In this experiment, we evaluated tadpole responses to
water conditioned by male and female frogs. We used the
data from experiment 2 for the tadpole response to water
conditioned by female frogs and the methods from
experiment 2 to measure the tadpole response to water
conditioned by male frogs. There were 15 replicates of
each treatment. We measured the tadpole response by
calculating the mean cumulative time tadpoles were
active. We first compared, with the Wilcoxon test, the
tadpole responses in the two treatments (distilled water
versus conditioned water). Then, with the Mann–
Whitney test we compared the tadpole responses in water
conditioned by female frogs versus water conditioned by
male frogs. However, because the tadpole response in
distilled water varied slightly each time, we adjusted it
(called adjusted tadpole response hereafter) by subtracting tadpole response time in distilled water from response
time in conditioned water.
Female frog versus tadpoles
We assessed tadpole responses to water conditioned by
a female frog, a female frog and tadpoles, and tadpoles
only. We used data from experiment 2 for the tadpole
response to water conditioned by female frogs. To prepare
the water conditioned by a female and tadpoles, we
placed a female frog and 10 tadpoles for 4 h in each of 10
beakers containing 50 ml of distilled water. The frogs and
tadpoles were removed and the conditioned water was
filtered and then pooled. The same procedures were used
to prepare the water conditioned by tadpoles only. We
used the methods from experiment 2 to measure the
tadpole response to water conditioned by female frogs
and tadpoles and tadpoles alone. There were 15 replicates
of each treatment. We measured the tadpole response by
calculating the mean cumulative time tadpoles were
active. We first compared with the Wilcoxon test the
tadpole responses in two treatments (distilled water versus conditioned water) for each of the three experiments.
Then, with the Kruskal–Wallis test we compared the
adjusted tadpole responses in water conditioned by
female frogs, female frogs and tadpoles, and tadpoles
alone. Multiple comparisons (Mann–Whitney test) were
performed if, and only if, the overall effect was
significant.
Male frog versus tadpoles
We assessed tadpole response to water conditioned by
male frogs only and by male frogs and tadpoles. We used
data from experiment 3 as a measure of tadpole response
to water conditioned by male frogs and distilled water. To
prepare water conditioned by a male and tadpoles, we put
50 ml of distilled water in each of 10 beakers and then
placed 10 tadpoles and a male frog in each beaker. After
4 h, the frog and tadpoles were removed, the conditioned
distilled water from each beaker was filtered, and then
pooled. We assessed tadpole response with the same
methods used in experiment 2. There were 15 replicates
in each treatment. We measured the tadpole response by
calculating the mean cumulative time tadpoles were
active. We first compared with the Wilcoxon test the
tadpole responses in two treatments (distilled water versus conditioned water) for each experiment. Then, with
the Mann–Whitney test we compared the adjusted
tadpole responses in water conditioned by male frogs
versus water conditioned by male frogs and tadpoles.
Results
Sex-specific chemical cues
Tadpoles in water conditioned by male frogs
moved significantly more than those in distilled water
(Wilcoxon test: T=3.96, N=15, P=0.0001; Table 1). There
was no significant difference in the adjusted tadpole
responses to water conditioned by male frogs or female
frogs (data from experiment 2; Mann–Whitney test:
U=139, N1 =N2 =15, NS; Table 1).
Female frog versus tadpoles
Tadpoles in the water conditioned by a female frog and
tadpoles moved significantly more than those in distilled
water (Wilcoxon test: T=4.59, N=15, P=0.0001; Table 1).
The activity level of tadpoles in water conditioned by
tadpoles only did not differ significantly from that in
distilled water (Wilcoxon test: T=1.22, N=15, P=0.236;
Table 1).
The adjusted tadpole responses to water conditioned by
a female frog only (data from experiment 2), a female and
tadpoles, or tadpoles only, were significantly different
(Kruskal–Wallis Test: 22 =30.609, P=0.0001). The adjusted
tadpole response in water conditioned by a female frog
only or a female and tadpoles was significantly longer
than in water conditioned by tadpoles alone (Mann–
Whitney test: U=214, N1 =N2 =15, P<0.001; U=222,
N1 =N2 =15, P<0.001, respectively). Furthermore, the
adjusted tadpole response in water conditioned by a
female and tadpoles was significantly longer than in
KAM & YANG: ANURAN FEMALE–OFFSPRING COMMUNICATION
water conditioned by a female alone (Mann–Whitney
test: U=188, N1 =N2, P<0.001).
Male frog versus tadpoles
Tadpoles in water conditioned by a male frog and
tadpoles moved significantly more than those in the
distilled water (Wilcoxon test: T=2.55, N=15 P=0.011;
Table 1). There was no significant difference in the
adjusted tadpole responses to water conditioned by
a male frog (data from experiment 3) or by a male frog
and tadpoles (Mann–Whitney test: U=130, N1 =N2 =
15, NS).
DISCUSSION
In C. eiffingeri and other anurans with uniparental care,
communication between females and their arboreal tadpoles involves complex behaviours mediated by tactile
and chemical cues. Begging and provisioning behaviours
are clearly the bases for the evolution of this communication system (Wilson 1980; Hoff et al. 1999). The most
conspicuous form of communication between C. eiffingeri
tadpoles and female frogs is egg-begging behaviour. This
behaviour has been described in detail for C. eiffingeri
(Ueda 1986), A. spinosa (Jungfer 1996) and D. pumilio
(Weygoldt 1980; Brust 1993). Chirixalus eiffingeri tadpoles
respond vigorously to conspecific males but not to female
frogs of a different species (Ueda 1986); however, male
frogs immediately move away when tadpoles nip them.
In our experiments, we found that some females
responded negatively to being nipped by tadpoles and
quickly moved away. Some tadpoles clung to the skin of
female frogs as they climbed out of the water (Y.-C. Kam,
personal observation). We speculate that the tadpoles’
nipping is discomforting or irritating to the female frogs.
We also suggest that the physiological readiness of a
female frog strongly affects her response to tactile stimulation from tadpoles. A female frog may be more tolerant
of tadpole nipping when she has mature eggs than when
she does not. In experiment I, female frogs did not lay
eggs during the 5 min they were confined with tadpoles,
probably because the interaction between tadpoles and
female frogs was too short, or female frogs were simply
not ready, or willing, to lay eggs.
Chirixalus eiffingeri tadpoles did not respond visually to
a female frog, regardless of whether she was moving. This
is consistent with the results of a preliminary laboratory
experiment on interactions between a C. eiffingeri female
and her offspring. We reared a pair of C. eiffingeri in a
terrarium where they deposited fertilized eggs in a
bamboo stump containing a pool of water. For a week, we
videotaped the bamboo stump from 1800 to 0600 hours.
The female C. eiffingeri slowly crawled up the outside of
the bamboo stump, stopping for a while, then continuing. During her ascent, tadpoles in the water pool
remained immobile. As soon as the female reached the
rim of the stump, she jumped into the pool. The tadpoles
immediately became extremely excited and started
begging. In contrast, visual cues are important components of female–tadpole communication in D. pumilio
(Weygoldt 1980; Brust 1993). The tadpoles show a
remarkable behaviour whenever an adult frog attempts to
enter their leaf axils. This behaviour often starts before a
frog has entered the leaf axil, triggered either by visual
cues of the approaching frog or by vibrations caused by its
movements (Weygoldt 1980). Instead of swimming with
the usual undulating tail movements, the tadpoles stiffen
their tails and rapidly vibrate them, producing conspicuous circular movements just beneath the water surface. A
frog motivated to bathe is deterred by these movements, often leaving before it has touched the water
and moving on to an empty axil for bathing (Weygoldt
1980). Dendrobates pumilio is diurnal, whereas C. eiffingeri
is nocturnal, which probably explains the greater importance of visual cues to female–tadpole communication in
D. pumilio.
Tadpoles placed in water conditioned by female frogs
(experiment 2) increased their activity but did not beg.
Thus, female frogs seem to give off water-soluble substances that stimulate tadpole activity. However, a female
must be physically present to induce begging. Tadpole
activity was stimulated even more by the water conditioned by a female frog and tadpoles, suggesting the
female and tadpoles interact in a synergistic manner. The
tadpole activity in water conditioned by a female frog and
tadpoles was far greater than the sum of the tadpole
activity in water conditioned by a female frog alone
and tadpoles alone (see experiment 2). Although water
conditioned by male frogs also elevated tadpole activity,
water conditioned by a male frog and tadpoles did not
increase tadpole activity further. Ueda (1986) reported
that C. eiffingeri tadpoles vigorously nip the skin of male
frogs, but the males move away as soon as they are
nipped. Thus, certain substances attractive to tadpoles
are given off by both sexes of C. eiffingeri. However,
only female frogs tolerate being nipped by tadpoles. If
female frogs are willing to be nipped by tadpoles, tadpole activity or movement may become faster and more
vigorous as the encounter progresses; in some cases this
communication triggers egg laying (Y.-C. Kam, personal
observation).
We hypothesize that the tactile stimulation from the
tadpoles mimics the tactile stimulation of male frogs
during amplexus, which induces the female frog to lay
eggs. Chemical cues appear to play an important role in
female–tadpole communication. In amphibians, chemical communication is a component of kin recognition by
anuran larvae (Waldman 1985, 1991; Blaustein & Walls
1995), predator avoidance (Manteifel 1995; Lefcort 1996;
Summey & Mathis 1996), and reproductive behaviour
(Forester 1986; Kikuyama et al. 1995). However, chemical
communication between female frogs and tadpoles is
novel. We do not know the identity of the chemical
compounds involved in female–tadpole interactions. To
understand fully the scope and importance of chemical
communication between female frogs and tadpoles,
further experimental studies and identification of the
active compounds are necessary. In addition, comparative studies of other species whose tadpoles show eggbegging behaviour, such as A. spinosa and D. pumilio, will
be crucial.
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ANIMAL BEHAVIOUR, 64, 6
Acknowledgments
This study was supported by a National Science Council
Grant (NSC 88-2311-B-018-001) to Y.-C.K. We thank the
staff of the Experimental Forest of the National Taiwan
University at Chitou for providing accommodation and
permitting us to collect specimens in the experimental
forest. Comments and suggestions on the manuscript by
A. F. Warneke are appreciated.
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