Limb segment contributions to the evolution of hind limb length in phrynosomatid lizards

Abstract

Longer hind limbs are often associated with faster maximum sprint speeds measured in the laboratory and sometimes with increased Darwinian fitness in studies of individual variation in natural populations. Limb length may be altered by changing the length of one or all segments, with different functional consequences. Segment length evolution can be influenced by both natural and sexual selection, and lineage-specific effects (multiple solutions) may also occur. We examined the evolution of total hind limb length, as well as thigh, crus, pes, and toe length, among 46 species of phrynosomatids and also investigated the role of habitat use and shared evolutionary history in shaping limb morphology. Because sexes are usually behaviourally and morphologically dimorphic, we examined them separately. In females, habitat was only an important predictor of crus (lower leg) length. In males, habitat was not an important predictor of any variable. Overall, clade-level differences were more important than habitat as predictors of segment or total hind limb length. Not all limb segments scaled isometrically with the combined length of other segments, and both sex and clade affected the scaling of some segments. These results suggest that clade-level differences are more important than habitat use for explaining differences in limb length and proportions, and sexual dimorphism may be an important consideration in morphology–performance–behaviour–fitness relationships. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2016, 117, 775–795.