Rapid dynamic colour change is an intrasexual signal in a lek breeding frog (Litoria wilcoxii)
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Bright colouration appearing in one sex only can be driven by components of sexual selection including female choice, male competition or mate recognition. Male Litoria wilcoxii undergo rapid colour change from brown to yellow during amplexus, however, the function, if any, is unknown. We tested possible behavioural functions by observing breeding aggregations and behavioural responses (colour change, movement, call and amplexus duration) to varying stimuli (including model male and female frogs). We also examined whether colour change was a by-product of hormone release by comparing spermatic urine of frogs injected with epinephrine (colour change hormone) and hCG (triggers spermiation). Finally, the predation cost of being bright yellow was examined by placing frog models (yellow and brown) in the field and measuring predator attack rate. The behavioural responses of males to model females, brown/brown models (female with amplexing brown male), and brown/yellow models (female with amplexing yellow male), were similar to reactions towards real females, with the important exception that males did not attempt amplexus with brown/yellow models. Epinephrine injections triggered colour change but not sperm release in male frogs, while hCG induced sperm release but not colour change. Attack rates were low in predation trials with no difference in attack rates between yellow and brown models observed. Our study presents a novel function for rapid dynamic colour change as an intrasexual signal during amplexus that could avert sperm competition and displacement by other males.
Colour displays during breeding are believed to have evolved through mechanisms of sexual selection (female choice, male–male competition or sexual recognition). Stony creek frogs (Litoria wilcoxii) have been observed to rapidly change colour from brown (similar to female colouration) to bright yellow during amplexus, which is unusual as the colour change occurs after mate selection. Behavioural experiments were used to test hypotheses on the evolutionary function of colour change in this species. In L.wilcoxii, colour functions as an intrasexual signal during amplexus, we hypothesise that this could avert sperm competition and/or displacement by other males during amplexus. The function presented here is novel among amphibians, however as data on dynamic colour change in amphibians is lacking, this trait may be more common.
KeywordsRapid colour change Amphibians Colour dimorphism Intrasexual selection Visual signals
This study was performed as part of the PhD research of CK. We acknowledge financial support from the Environmental Futures Research Institute (EFRI) and the School of Environment at Griffith University, Australia. This study was carried out under permit WISP13675913 issued by the Queensland Department of Environment and Heritage Protection (DEHP) and the Griffith University Animal Ethics Committee (AEC) approved the experiments (permit no. ENV/20/12/AEC). We would like to thank the two anonymous reviewers who provided helpful modifications to an earlier draft. Thanks to all the volunteers who assisted with field work especially Basam Tabet, Patricia Hall and Sonia Marsonic.
Compliance with ethical standards
All applicable international, national and/or institutional guidelines for the care and use of animals were followed. This study was carried out under permit WISP13675913 issued by the Queensland Department of Environment and Heritage Protection (DEHP) and the Griffith University Animal Ethics Committee (AEC) approved the experiments (permit no. ENV/20/12/AEC).
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