Prey Chemical Discrimination and Foraging Mode in Gekkonoid Lizards

Relationships among phylogeny, foraging mode, and prey chemical discrimination by tongue-flicking were investigated by experimentally testing for the presence of lingually mediated prey chemical discrimination in representatives of two families of gekkonoid lizards having different foraging modes. In the experiments, the tongue-flicking and biting responses of each lizard were recorded in response to cotton swabs bearing three classes of stimuli: prey surface chemicals, cologne as a pungency control, and deionized water as an odorless control. In a eublepharid species, Eublepharis macularius, the tongue-flick rate, the proportion of individuals attacking the swab, and a composite measure combining effects of tongue-flicking and attack (TFAS(R)) were significantly higher and the latency to attack significantly shorter in the prey stimulus condition than in the other conditions, which did not themselves differ. In contrast, no tongue-flicking or attacks were observed in any of the conditions for two gekkonid species, Thecadactylus rapicauda and Gekko gecko. Because eublepharids are active foragers whereas gekkonids are ambush foragers, prey chemical discrimination was associated with active foraging, as predicted. Prior to this report, all families of ambush-foraging lizards known to lack prey chemical discrimination belonged to a single clade, Iguania. Actively foraging carnivorous lizards identify prey by chemical cues and belong to Scleroglossa, which includes the families studied here. It is argued that adoption of active foraging may have induced selection for gain of prey chemical discrimination involving tongueflicking in eublepharids. Phylogeny and the presence or absence of prey chemical discrimination are closely related in lizard families because foraging mode is conservative in the major clades Iguania and Scleroglossa.