Sexual Dimorphism as It Relates to Natural History of Leopard Lizards (Crotaphytidae: Gambelia)

Sexual dimorphism is a phenomenon that occurs in a variety of animal taxa, and its occurrence can reflect and/or influence crucial aspects of the natural history of organisms. We examined the external morphology of three lizard species, Gambelia sila, G. wislizenii, and G. copei. Gambelia sila shows the prevalent sexually dimorphic condition among iguanian lizards of males attaining a larger head relative to body size (snout-vent length) and larger overall body size than females, whereas in G. wislizenii and G. copei, females attain a larger body size than males. We performed a detailed morphometric examination of these three taxa to (1) characterize interspecific differences in sexual dimorphism among these three closely related lizards, (2) test the hypothesis that sexual dimorphism in cranial shape exists in G. wislizenii and G. copei, and (3) examine intersexual body size and cranial shape variation among G. wislizenii populations inhabiting major North American geophysical regions. Morphometric analyses support the results of previous studies. Cranial shape dimorphism is present in some G. wislizenii populations, particularly those of the Great Basin, and in G. copei. Interregional comparisons reveal that G. wislizenii populations vary both in the degree of intersexual body and head size differences as well as in cranial shape dimorphism. Among regional groups, body and head size and cranial shape dimorphism exhibit an inverse relationship. These patterns of morphological variation are correlated with aspects of the ecology, behavior, and phylogenetic history of these taxa.