Tandem evolution of diet and chemosensory responses in snakes

Abstract

AbstractAdaptations to foraging requirements have molded sensory capacities of animals in intriguing and sometimes spectacular ways, including evolution of echolocation by bats and infrared detection by pitvipers, as well as of location of prey using lingually sampled chemical cues by actively foraging lizards. Among snakes, specialized diets and geographic differences in diets have evolved many times. Because snakes identify prey by vomerolfactory analysis of chemicals sampled by tongue-flicking, it may be predicted that responsiveness to lingually sampled chemical cues corresponds to diet: It should be much stronger to prey included in than excluded from specialized diets and should covary with geographic dietary differences in prey generalists. Breeding studies in Thamnophis elegans showed that greater responsiveness to local prey in populations having geographically variable diets has a heritable component. Whether strong chemosensory response evolves to match current diet has not been established for snakes using the comparative method. For all paired comparisons of dietary change now available, chemosensory behavior changed so that strongest responses were limited to cues from the current prey. Because diets were specialized and snakes were ingestively naive hatchlings in almost all comparisons, the basis for observed relationships is innate rather than experiential. Snake chemosensory responses have evolved to match current diets.