Meeting Abstract
Many animals utilize their jaw muscles to capture and consume prey, while some also use their jaws to bite competitors during combat. Jaw morphology may thus have evolved in association with diet, social behavior, or a combination of these factors. In this study, we use a diverse group of six lizard species to test the hypothesis that species with greater dietary niche breadth, those that consume other vertebrates, and those that use their jaws in combat, have larger relative head dimensions and jaw muscles. Three of our focal species are insectivores that are opportunistically saurophagous (i.e., consume other lizards): green anole lizards (Anolis carolinensis), Texas spiny lizards (Sceloporus olivaceus), and northern curly tails (Leiocephalus carinatus). The other three species in this study are exclusively insectivorous: Mediterranean house geckos (Hemidactylus turcicus), little brown skinks (Scincella lateralis), and spotted whiptails (Aspidoscelis gularis). Of this group, only green anoles regularly use jaws in male combat. For each of these six species, we collected dried jaw muscle mass of 3-6 males, and for 10 males per species, we measured SVL (snout-vent-length), body mass, head length, head width, and head depth. We estimated dietary niche breadth by the total number of taxonomic orders of prey consumed by each genus, as reported in the herpetological literature. Results show that saurophagous species had relatively greater jaw muscle mass and larger heads than non-saurophagous species, with green anoles (the species that uses biting in combat) exhibiting the largest jaw muscle mass of the group. In addition, dietary breadth was positively associated with relative jaw muscle mass. Together, these results suggest that jaw morphology has evolved as a function of both diet and social behavior in lizards.
