“Consistent associations between body size and hidden contrasting color signals across a range of insect taxa”
Karl Loeffler-Henry, Changku Kang, Thomas N. Sherratt (July 2019)
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The evolution of hidden contrasting coloration is associated with body size in insects
Hidden conspicuous color signals are evolutionarily associated with large body size in insects
Coloration frequently serves to protect insects from visual predators through crypsis, warning signals, and mimicry. While these color patterns are often permanently displayed, some insect species use their anti-predatory color signals more dynamically: they normally remain camouflaged, but reveal conspicuous colors transiently upon approach by predators. Recent studies have demonstrated that such flash (in moving prey) and deimatic (in stationary prey) conspicuous displays are more effective in deterring predators when exhibited by larger prey than smaller prey. Thus, one might expect that hidden conspicuous color signals would be more likely to be found in large than small prey species. The collaborative research team between Carleton University and Mokpo National University tested this hypothesis in five different insect groups that are known to utilize hidden conspicuous color signals: Orthoptera, Mantidae, Phasmatidae, Saturniidae, and Sphingidae. Our findings suggest that after controlling for the effect of shared ancestry, the presence of hidden conspicuous color signals is indeed associated with large size in most of the studied insect taxa. These results therefore provide further evidence that anti-predator traits in insects is at least in part mediated by body size.
While there have been a number of recent advances in our understanding of the evolution of animal color patterns, much of this work has focused on color patterns that are constantly displayed. However, some animals hide functional color signals and only display them transiently through behavioral displays. These displays are widely employed as a secondary defense following detection when fleeing (flash display) or when stationary (deimatic display). Yet if displays of hidden colors are so effective in deterring predation, why have not all species evolved them? An earlier study suggested that the hidden anti-predatory color signals in insects are more likely to have evolved in species with large size because either (or both): i) large cryptic prey are more frequently detected and pursued and ii) hidden color signals in large prey are more effective in deterring predation than small prey. These arguments should apply universally to any prey that use hidden signals so the association between large size and hidden contrasting color signals should be evident across diverse groups of prey. In this study, we tested this prediction in five different groups of insects. Using phylogenetically controlled analysis to elucidate the relationship between body size and color contrast between forewings and hindwings, we found evidence for the predicted size-color contrast associations in four different groups of insects, namely Orthoptera, Phasmatidae, Mantidae, Saturniidae, but not in Sphingidae. Collectively, our study indicates that body size plays an important role in explaining variation in the evolution of hidden contrasting color signals in insects.