Plant chemical discriminations by an herbivorous iguanid lizard, Sauromalus ater

We experimentally studied the ability of the iguanid lizard Sauromalus ater to discriminate between plant and animal foods and control stimuli using o nly chemical cues. When chemicals were presented on cotton swabs, the lizar ds exhibited stronger responses, as indicated by tongue-flicking and biting , to chemical stimuli from romaine lettuce than from crickets and control s ubstances. Responses to plant and animal food did not differ significantly in S. ater, which eats animal prey only occasionally in natural populations . Although there were no significant differences between responses to crick et chemicals and other stimuli for the entire data set, those individuals t hat ate or attacked crickets tongue-flicked at high rates in response to cr icket chemicals. Based on the presence of herbivory and plant chemical disc rimination in three iguanid genera, it is likely that plant chemical discri mination is ubiquitous in iguanids. Given the uncertainty of iguanian phylo geny, the evolution of herbivory and response to plant chemicals cannot be traced with confidence. However, it appears very likely that lingually medi ated plant chemical discriminations evolved in the common ancestor of Iguan idae or earlier in iguanian history in response to a shift to an herbivorou s diet.