Consistent Associations between Body Size and Hidden Contrasting Color Signals across a Range of Insect Taxa.

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 display them only 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 antipredatory 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 or (ii) hidden color signals in large prey are more effective in deterring predation than in 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 hind wings, we found evidence for the predicted size-color contrast associations in four different groups of insects, namely, Orthoptera, Phasmatidae, Mantidae, and 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.