Male nuptial display colour and vocalisation appear to signal independent information in the whirring tree frog

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Abstract
When different modes of communication are used in combination and for example convey visual and acoustic information, they form a multimodal signal. Frogs are best known for using acoustic communication, but many species also use visual or colour signals, some of which are dynamic, and may be combined with acoustic signals. In this context, the question of whether these two modes of communication reinforce the same message or offer different information is poorly understood. Male whirring tree frogs, Litoria revelata, use a multimodal signal during courtship, which combines a vocalisation and dynamic sexual dichromatism, with nuptial display colours shifting from brown or grey to bright yellow. Here, we examined the properties of the advertisement call and nuptial colour of vocalising male whirring tree frogs and tested whether the two signals were likely to reinforce each other or convey independent information. We found only weak associations between elements of male colouration and vocalisations, suggesting that advertisement calls and nuptial colour do not reinforce each other and that the signals may instead convey different information. Significance statement: Dynamic nuptial colour and vocalisation in combination is a relatively common multimodal signal in frogs but is unstudied. We looked for relationships between properties of colour and vocalisation in an Australian tree frog to explore whether the two sensory modes formed backup signals or multiple messages. We did not find predictive relationships between nuptial colour and vocalisation, supporting the multiple messages hypothesis and suggesting that nuptial colour is not necessarily directed at females for the purposes of mate attraction, potentially differing from the assumed function of the vocalisation. Our study is also the first to formally characterise aspects of dynamic sexual dichromatism in the whirring tree frog (Litoria revelata) and the first to describe the advertisement call of this species in its southern distribution. Whilst we do not specifically address the function of dynamic sexual dichromatism in this species, our findings do not contradict the existing literature in respect to it being a male-male directed signal.
Funding Information
  • Macquarie University
  • Frog and Tadpole Study Group NSW
  • University of New England

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