Résumé
Predators often avoid toxic, unpalatable, or otherwise unprofitable prey because of innate biases or past unpleasant experiences. In both cases, the association between prey appearance and unprofitability has favored an anti-predator strategy called “aposematism” (Poulton, 1890). In short, aposematic prey benefit from reduced predation because predators perceive the prey phenotype as a warning (Wallace, 1882). Aposematic traits take the form of spectacular conspicuous colorations in many taxa, in particular in snakes (Smith, 1977), amphibians (Rudh and Qvarnström, 2013), insects (Wilson et al., 2015; Motyka et al., 2018) and spiny plants (Lev-Yadun, 2016). As such, they have enthralled many evolutionary biologists and ecologists, whose research greatly improved our understanding of local adaptation (Mallet and Barton, 1989), speciation (Merrill et al., 2012), community dynamics (Chazot et al., 2014), and predator foraging decisions (Skelhorn et al., 2016). In the literature, aposematism is therefore often equated with colorations that are consistently conspicuous (but see recent studies on “switchable” aposematic signals; e.g., Kang et al., 2016a,b). We argue here that this focus on conspicuous colorations has led to researchers overlooking other components of prey phenotype. Aposematism relies not only on “signaling traits” (like conspicuous coloration), which evolve through natural selection imposed by predators, but also on “cues” (e.g., body shape, behavior, or non-conspicuous coloration), the evolution of which is determined mainly by environment, sexual selection or developmental constraints (Maynard-Smith and Harper, 2003; Scott-Phillips, 2008). In this opinion piece, we aim at highlighting the underappreciated role of cues in the evolution of warning signals in the context of protective mimicry.