Meeting Abstract
In lizards, longer hind limbs are often associated with faster maximum sprint speeds measured in the laboratory and sometimes with increased Darwinian fitness in studies of natural populations. Limb length may be altered by changing the length of one or all segments, with different functional consequences. For example, longer thighs may lead to increased speed by limb elongation, but could also decrease maneuverability by increasing the lateral extent of the limbs in a sprawling posture. Segment length evolution can be influenced by lineage-specific effects (multiple solutions), natural, and sexual selection. We examined segment evolution among 46 species of phrynosomatids. Because the sexes may be behaviorally dimorphic, we examined them separately to reveal any dimorphism in limb evolution. Limb segments do not scale isometrically with the combined length of the other segments; the thighs and toes of phrynosomatids are relatively shorter in species with longer hind limbs. Cophosaurus, Holbrookia, and Uma species have significantly longer hind limbs for their body size than other phrynosomatids. Phrynosoma have significantly longer crura and shorter toes for their body size than other species. Variation in hind limb length and segment lengths is not explainable by habitat use. Males in the genus Sceloporus have significantly longer hind limbs for their body size compared to other phrynosomatids, but this difference is not apparent in females. These results suggest that clade-level differences are more important than habitat use for explaining differences in limb length/proportions, and sexual dimorphism may be an important consideration in morphology-performance-behavior-fitness relationships.
