Abstract

Aposematic insects use bright colours and/or distinct markings to advertise their toxins to potential predators. When toxins are bitter-tasting and detectable upon attack, birds are able to use taste when making decisions about whether or not to eat defended prey. Taste-rejection behaviour, when birds taste but do not ingest a prey item, is often assumed to increase the survival of defended prey, yet few empirical studies have investigated the post-attack survival rates of live defended insects. We used naive domestic chicks (Gallus gallus domesticus) foraging on live waxmoth larvae (Galleria mellonella) in a laboratory setting, where conspicuousness and distastefulness could be controlled and manipulated to investigate the effects of taste-rejection behaviour, as well as the associated handling behaviour, on post-attack survival of prey. We found that being distasteful increased the probability of being rejected by naive chicks, and taste-rejection behaviour tended to be more frequent when distasteful prey were conspicuous compared with when they were cryptic. Conspicuous coloration also appeared to affect predators’ assessment of prey distastefulness, with past experience strongly influencing the probability that conspicuous (but not cryptic) prey were rejected. However, in contrast to previous findings, there was no evidence that either distastefulness or conspicuousness altered how predators handled the prey before making a decision about whether or not to eat it, in any way that enhanced prey survival post-attack. Therefore, taste-rejection behaviour appears to be a useful measure of prey survival. Our results provide novel insights into the potential importance of signal conspicuousness for prey populations with variable defences, and highlight the need to consider the role of taste-rejection behaviour in mimicry dynamics.

Highlights

  • Conspicuous coloration can change the post-attack behaviour of predators, and can increase the probability that a distasteful prey item is released

  • 2006a,d; Wiklund & Ja€rvi, 1982), when they are conspicuous compared with cryptic (Halpin et al, 2008a,b)

  • The mortality of prey differed depending on whether they were distasteful or not: the mortality of distasteful prey was significantly lower than that of undefended prey (P = 0.035; see Table 1A). This appeared to be due to whether or not a prey was rejected rather than the ways in which predators handled the prey prior to rejection: the distasteful prey had an overall higher probability of being taste-rejected than the undefended prey (P = 0.032; see Table 1A), but there was no difference in the proportions of distasteful and undefended prey that survived after being rejected (P > 0.05; see Table 1A)

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Summary

Introduction

Insects display a diverse range of defence mechanisms, including adaptations to avoid being detected or caught by predators (Cott, 1940; Cuthill et al, 2005), as well as physical and chemical defences to deter ingestion if discovered (Atkins, 1980; Bowers, 1992; Cott, 1940; Eisner & Meinwald, 1966; Friedlander, 1976; Guilford, 1988; Hauglund et al, 2006). Species that use chemical defences are often brightly coloured, or have other conspicuous signals, to advertise their unpalatability to potential predators; a mode of defence referred to as ‘aposematism’ (Atkins, 1980; Cott, 1940; Friedlander, 1976; Guilford, 1988; Mappes et al, 2005; Poulton, 1890; Rowe & Halpin, 2013). Many aposematic insects produce externally detectable bitter-tasting chemicals (Nishida, 2002), and predators can reject prey postattack on the basis of their distastefulness

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