Chemical Discrimination of Potential Food Items by a Xantusiid Lizard, Lepidophyma flavimaculatum

Abstract

Lingually mediated chemosensory identification of food is widespread in scleroglossan lizards, and has been studied in representatives of all but a few families (Cooper, 1994a, 1995, 1997). It is strongly linked to active foraging mode, having been lost in taxa that secondarily adopted ambush foraging (Cooper, 1995; 1999a). One of the few major unstudied groups is the North and Central American family Xantusiidae, for which foraging mode also is unknown. Insectivorous xantusiids are anachoretic (Zweifel and Lowe, 1966; Del Toro, 1982; Bezy, 1988), i.e., they occupy narrow spaces that restrict access by predators (Edmunds, 1974), which makes their foraging difficult to observe. Although it might be thought that chemical senses would be useful to locate food at night or in enclosed spaces having limited light, most nocturnal gekkonid lizards are ambush foragers (Cooper, 1994a). Thus, the presence or absence of prey chemical discrimination of xantusiids cannot be predicted a priori. If they do detect and identify foods using chemical cues, it may be predicted that they tongue-flick and bite more in response to food than to various nonfood sources of organic and inorganic chemical cues. I experimentally studied chemosensory responses to food and a variety of other stimuli by observing tongue-flicking, which indicates chemical sampling for vomerolfaction (Cooper and Burghardt, 1990a; Halpern, 1992), and biting, which is a predatory attack, in the xantusiid Lepidophyma favimaculatum. This Central American species is known in the pet trade as the bark lizard because it is often found hiding during daylight hours in narrow spaces under bark of decaying fallen trees, but it also occupies rock crevices (Del Toro, 1982). The lizards emerge at night to climb on trees or rocks in search of food (Del Toro, 1982). Because L. flavimaculatum is an insectivore, I predicted that any discrimination among stimuli by this species would be manifested by stronger response to chemical stimuli from animal food than from plants or other control substances. Previous work with two species of primarily herbivorous lizards shows that they respond strongly to both animal and plant food chemicals (Cooper and Alberts, 1990; Cooper, 2000b). However, under the hypothesis that chemosensory responsiveness is adjusted to match diet, insectivores which do not eat plants should not respond to plant chemicals by elevated tongue-flick and biting rates. Plant chemicals from species palatable to herbivores were among the stimuli used as a first test of this hypothesis for an insectivore.