Abstract Chemically defended animals often display conspicuous colour patterns that predators learn to associate with their unprofitability and subsequently avoid. Such animals, known as aposematic, deter predators by stimulating, for
Chemically defended animals often display conspicuous colour patterns that predators learn to associate with their unprofitability and subsequently avoid. Such animals, known as aposematic, deter predators by stimulating, for example, their visual and chemical sensory channels. Thus, aposematism is considered to be ‘multimodal’, which is advantageous because multimodal signals provide to the receiver more information per unit of time than unimodal signals. Despite this being widely known, the different components of aposematic signals tend to be studied in isolation, with most studies focusing on the visual signals. Novel visual signals of aposematic prey are expected to be selected against due to positive frequency-dependent selection, but nature has a wide range of examples of variation among aposematic prey which contradict evolutionary expectations, leaving us wondering how such variation can arise and persist. Using a polytypic poison frog (Dendrobates tinctorius), we explored the forces of selection on variable aposematic signals using two phenotypically distinct (white, yellow) populations. We analysed their skin alkaloids both qualitatively and quantitatively, and then evaluated the efficacy of their visual signals and chemical defences in trials with model predators in the laboratory. Contrary to expectations, the skin extracts from yellow frogs, which had lower amounts of alkaloids, provoked higher aversive reactions by birds than white frogs. Likewise, predators learned to avoid the yellow signal faster than the white signal, and generalized their learned avoidance of yellow but not white. We suggest that signals that are easily learned and broadly generalised can protect rare, novel signals, while weak warning signals can persist in the absence of gene flow. Finally, we highlight the importance of accounting for variation in both components of multimodal aposematic displays, and to test that this variation evokes differential response in relevant predators.
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Maria Tello Ramos, Niki Khan, Nick Jones