Prey, but not plant, chemical discrimination by the lizard Gerrhosaurus nigrolineatus
We experimentally studied responses to food chemicals by Gerrhosaurus nigrolineatus, amember of a lizard genus endemic to subsaharan Africa. Gerrhosaur diets vary from insectivorous to omnivorous with a very large plant portion. The omnivorous G. validus responds strongly to chemical cues from prey and food plants. Because plants form a far smaller fraction of the diet of G. nigrolineatus, which is generally considered to be an insectivore, a correspondence between diet and chemosensory responsiveness predicts that G. nigrolineatus should respond strongly to prey chemicals, but more weakly than G. validus to plant food chemicals. Chemical stimuli were presented on cotton swabs. The lizards performed more tongue-flicks and bit more swabs bearing prey chemicals than control stimuli, but no strong responses were elicited by chemical stimuli from romaine lettuce, banana, or dandelion, plants that are highly palatable to herbivorous lizards. The contrast between responses to plant chemical stimuli by the two species of gerrhosaurs suggests that responsiveness to plant chemicals is adjusted to dietary plant intake, appearing in tandem with consumption of a diet having a large plant component. Additional observations suggest that movement triggers attack on prey and that airborne chemicals may contribute to detection of food chemicals.
Key words: behaviour, omnivory, food chemical discrimination, Squamata, Gerrhosauridae.