Event:

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 visual signals. Novel 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 and leave us wondering how this variation can arise and persist. Using a polymorphic tiger moth (Arctia plantaginis) and a polytypic poison frog (Dendrobates tinctorius), we explore the forces of selection on variable aposematic signals at different scales, and study predator response to the visual and chemical components of their multimodal warning signals. Our findings in both systems highlight the importance of accounting for variation in both components of multimodal aposematic displays, and, most importantly, of testing whether or not relevant predators react differently to this variation, as they are the ultimate selective agents in predator-prey systems.