Multisensory modalities increase working memory for mating signals in a treefrog

Animal choruses, such as those found in insects and frogs, are often intermittent. Thus females sampling males in the chorus might have to remember the potential mates’ calls during periods of silence. Although a number of studies have shown that frogs use multimodal signals, usually acoustic plus visual, no studies have tested the hypothesis that multimodal sexual signals increased working memory in females in the context of mate choice.

We tested this hypothesis in serrate-legged small treefrogs (Kurixalus odontotarsus) whose males produce advertisement calls accompanied by conspicuous vocal sac inflation. Females were presented with acoustic or/and acoustic + visual (dynamic sac shown by video) mating calls.

We found that females prefer multimodal calls over audio-only calls. Furthermore, multimodal calls are still preferred after a silent period of up to 30 seconds, a time span that covers the average silent period of the chorus. This was not true of audio-only calls.

Our results demonstrate that a multimodal signal engages working memory to a greater degree than does a unimodal signal, and thus female memory favours the evolution of multimodal signals in males through sexual selection. Selection might also favor female preference for multimodal signals if greater memory of a more complex male’s call facilitates mate searching and assessment.