Aposematic coloration enhances chemosensory recognition of noxious prey in the garter snakeThamnophis radix

Abstract

Considerable recent research has suggested that predators learn to avoid noxious or unpalatable prey more rapidly if those prey have conspicuous (aposematic) colour patterns. However, the precise psychological mechanisms by which predators associate conspicuous coloration with unpalatability remain poorly understood. In this study, the relative importance of visual and chemosensory information in learned aversions to noxious prey was examined by offering garter snakes two different types of prey (fish and earthworms) on forceps with varying colour patterns. Experimental subjects received injections of LiCl to induce illness immediately following the consumption of fish offered on either aposematic (yellow-and-black) or non-aposematic (green) forceps. Following their induced illness, snakes within both the aposematic and non-aposematic treatment groups showed significant aversions to fish, and avoided fish regardless of the colour of the forceps with which fish were offered. However, the aversion to fish was markedly stronger among snakes in the aposematic treatment group than in the non-aposematic group. These results indicate that aposematic coloration enhances chemosensory learning; aversions to unpalatable prey are formed more readily if the prey is conspicuously coloured, even though recognition of unpalatable prey depends on the prey's chemosensory characteristics rather than its coloration. Future responses to unpalatable prey are therefore influenced by an unexpectedly complex interaction of visual and chemosensory information acquired during the initial encounter.