Body Size Is Positively Correlated With Conspicuous Coloration in Ambystoma Salamanders, but Negatively Correlated With Conspicuous Coloration in Plethodon Salamanders

Monica M. Winebarger,Michael M. Gangloff,Lynn Siefferman,M. Worth Pugh,Michael S. Osbourn

doi:10.3389/fevo.2018.00143

Monica M. Winebarger, Michael M. Gangloff + Show 3 more

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https://doi.org/10.3389/fevo.2018.00143

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Abstract

Conspicuous coloration coupled with secondary defensive mechanisms is known as aposematic coloration and is used in predator avoidance and defense. Classic theory argues that aposematic signals tend to be more effective in larger organisms as they are intrinsically more easily detected by predators and are also more profitable prey items. Thus, it has been hypothesized that conspicuous coloration evolves in tandem with increased body size in aposematic prey because this likely increases the visibility and efficacy of the signal. To test this hypothesis, we used a comparative phylogenetic approach to investigate associations between body size and conspicuous coloration in two North American salamander genera: Ambystoma and Plethodon, both of which secrete noxious compounds to deter predators. Our analyses showed that increased conspicuous coloration co-evolved with increased body size in Ambystoma, yet we found the opposite relationship in the Plethodon clade. We speculate this is likely because Ambystoma are generally larger than Plethodon and exhibit gregarious mating behavior. Future studies should explore the toxicity of slimy skin secretions and how this may contribute to aposematic signaling in salamanders.

Highlights

Animals use a variety of visual signals to convey information to one another, including conspicuous coloration (Wallace, 1867)
When conspicuous coloration is coupled with a secondary defense, such as venom or poison, color is thought to serve as a signal of unpalatability to potential predators via aposematic signaling (Poulton, 1890)
Experimental evidence from a study examining the responses of naïve domestic chicks (Gallus gallus domesticus) to varying sizes of conspicuously colored ground bugs (Lygaeidae) suggests that aposematic signal efficacy increases with increasing body size (Gamberale and Tullberg, 1996a)

Summary

Introduction

Animals use a variety of visual signals to convey information to one another, including conspicuous coloration (Wallace, 1867). Cott (1940) suggested that aposematic signals typically involve red, yellow, or white patterns on a black background, likely because they are detected, recalled, and associated with the defense by predators (Gittleman and Harvey, 1980) Salamander Body Size and Conspicuousness hypothesized that larger animals are more likely to evolve conspicuous coloration compared to smaller animals for several reasons. Larger animals are intrinsically more obvious to predators than smaller animals and are more likely to evolve secondary defensive mechanisms (Hossie et al, 2015), and are less likely to benefit from cryptic coloration (Hagman and Forsman, 2003). Because smaller animals are less detected, they are less likely to benefit from conspicuous coloration (Hossie et al, 2015). Experimental evidence from a study examining the responses of naïve domestic chicks (Gallus gallus domesticus) to varying sizes of conspicuously colored ground bugs (Lygaeidae) suggests that aposematic signal efficacy increases with increasing body size (Gamberale and Tullberg, 1996a)

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