Multimodal Aposematic Signals and Their Emerging Role in Mate Attraction

Abstract

Chemically defended animals often display conspicuous color patterns that predators learn to associate with their unprofitability and subsequently avoid. Such animals (i.e., aposematic), deter predators by stimulating their visual and chemical sensory channels. Hence, aposematism is considered to be "multimodal." The evolution of warning signals (and to a lesser degree their accompanying chemical defenses) is fundamentally linked to natural selection by predators. Lately, however, increasing evidence also points to a role of sexual selection shaping warning signal evolution. One of the species in which this has been shown is the wood tiger moth, Arctia plantaginis, which we here put forward as a promising model to investigate multimodality in aposematic and sexual signaling. A. plantaginis is an aposematic diurnal moth which exhibits sexually dimorphic coloration as well as sex-limited polymorphism in part of its range. The anti-predator function of its coloration and, more recently, its chemical defenses (even when experimentally decoupled from the visual signals), has been well-demonstrated. Interestingly, recent studies have revealed differences between the two male morphs in mating success, suggesting a role of coloration in mate choice or attraction, and providing a possible explanation for its sexual dimorphism in coloration. Here, we: (1) review the lines of evidence showing the role of predation pressure and sexual selection in the evolution of multimodal aposematic signals in general, and in the wood tiger moth in particular;(2) establish gaps in current research linking sexual selection and predation as selective pressures on aposematic signals by reviewing a sample of the literature published in the last 30 years; (3) highlight the need of identifying suitable systems to address simultaneously the effect of natural and sexual selection on multimodal aposematic signals; and (4) propose directions for future research to test how aposematic signals can evolve under natural and sexual selection.

Multiple modalities in insect warning displays have additive effects against wild avian predators

“…We are increasingly becoming aware that multimodal signalling comprising more than just two modalities is ubiquitous in the animal kingdom (de Luna et al 2010;Higham and Hebets 2013;Starnberger et al 2014;Rojas et al 2018). Our study provides evidence that the multicomponent bimodal display of aposematic insects may elicit responses in predators that cannot be predicted by studying each signal mode in isolation.…”

“…Multimodal signals are prominent in animal communication across different taxa (Hölldobler 1999;Partan and Marler 1999;Cooper and Goller 2004;Ratcliffe and Nydam 2008;Bradbury and Vehrencamp 2011;Higham and Hebets 2013;Rojas et al 2018). As such, many attempts have been made to identify their role(s) in various contexts, their mechanisms of sensory exploitation in the receiver(s) and their evolutionary pathways (Partan and Marler 1999;Rowe and Guilford 1999;Hebets and Papaj 2005;Partan 2013;Higham and Hebets 2013;Starnberger et al 2014).…”

Species specificity and intraspecific variation in the chemical profiles of Heliconius butterflies across a large geographic range

“…Genital compounds were originally suggested to form part of the antipredation signal (Eltringham, 1925). We detected 2‐s‐butyl‐3‐methoxypyrazine in the genitals of H. melpomene , H. cydno , and H. timareta , and 2‐isobutyl‐3‐methoxypyrazine in the genitals of H. melpomene and H. cydno , both compounds known to deter predators in the wood tiger moth (Burdfield‐Steel, Pakkanen, Rojas, Galarza, & Mappes, 2018; Rojas et al, 2017, 2018; Rojas, Mappes, & Burdfield‐Steel, 2019). More generally, methoxypyrazines act as warning odors in other insects (e.g., Lepidoptera, Rothschild, Moore, & Brown, 1984; fireflies, Vencl et al, 2016), effective against avian predators (Guilford, Nicol, Rothschild, & Moore, 1987).…”

“…The role of chemical signaling is likely to be especially important in comimics, where visual signals alone are not sufficient to identify conspecifics (Estrada & Jiggins, 2008; Giraldo, Salazar, Jiggins, Bermingham, & Linares, 2008; Mérot et al, 2013; Sánchez et al, 2015). In contrast, chemical compounds could be part of a multimodal aposematic warning signal (Rojas et al, 2018; Rothschild, 1961), with some tentative evidence that comimics exhibit similar chemical bouquets to aid recognition by predators (Mann et al, 2017).…”

Effectiveness of the aposematic Eumaeus childrenae caterpillars against invertebrate predators under field conditions

“…Chemically defended animals often deter predators by stimulating their visual and chemical sensory channels (Rojas et al, 2018). The aposematic coloration of prey is a defense mechanism against visual predators (Dell'Aglio et al, 2016).…”