Chemosensory responses to sugar and fat by the omnivorous lizard Gallotia caesaris - With behavioral evidence suggesting a role for gustation

Many lizards can identify food using only chemical cues, as indicated by to ngue-flicking for chemical sampling and biting, but the effectiveness of th e chemical components of food are unknown, as is the relationship between r esponse strength and concentration. We investigated responses by the omnivo rous lizard Gallotia caesaris to representatives of two major categories of organic food chemicals, lipids and carbohydrates. The stimuli, pork fat an d sucrose solutions of varying concentration, were presented to lizards on cotton swabs and their lingual and biting behaviors were observed during 60 -s tests. In the first experiment, fat elicited more tongue-flicks and bite s than saturated sucrose or water (odorless control), biting being limited to the fat condition. Lizards licked at high rates, but exclusively in resp onse to sucrose, A lick was a lingual protrusion in which the dorsal surfac e of the tongue contacted the swab, in contrast to the anteroventral contac t made during tongue-flicks. In a second experiment, the number of ticks, b ut not the number of tongue-flicks, increased with the concentration of suc rose. The results indicate that lipids contribute to prey chemical discrimi nation and are adequate to release some attacks, but are not as effective a s releasers of attack as mixtures of prey chemicals obtained from prey surf aces. The findings with respect to licking are novel, and suggest that lick ing may be a response to gustatory stimulation by sugar, in contrast to pre viously observed prey chemical discriminations shown to require vomerolfact ion. (C) 2001 Elsevier Science Inc. All rights reserved.