Functional basis for sexual differences in bite force in the lizard Anolis carolinensis

In many species of lizards, males attain greater body size and have larger heads than female lizards of the same size. Often, the dimorphism in head size is paralleled by a dimorphism in bite force. However, the underlying functional morphological basis for the dimorphism in bite force remains unclear. Here, we test whether males are larger, and have larger heads and bite forces than females for a given body size in a large sample of Anolis carolinensis. Next, we test if overall head shape differs between the sexes, or if instead specific aspects of skull shape can explain differences in bite force. Our results show that A. carolinensis is indeed dimorphic in body and head size and that males bite harder than females. Geometric morphometric analyses show distinct differences in skull shape between males and females, principally reflecting an enlargement of the jaw adductor muscle chamber. Jaw adductor muscle mass data confirm this result and show that males have larger jaw adductors (but not jaw openers) for a given body and head size. Thus, the observed dimorphism in bite force in A. carolinensis is not merely the result of an increase in head size, but involves distinct morphological changes in skull structure and the associated jaw adductor musculature.