A COMPARATIVE-STUDY OF THE EVOLUTION OF SCELOPORUS PUSH-UP DISPLAYS

Comparative studies are often used to infer the evolutionary histories of phenotypic traits. In this study, hypotheses suggesting that the evolution of Sceloporus push-up displays was constrained by the evolution of body size and the adoption of an arboreal lifestyle are tested with data from the literature on the push-up displays of 42 species of Sceloporus lizards and several phylogenetic comparative method techniques including independent contrasts, inferred changes, and spatial autocorrelation methods. Comparisons are made among the various phylogenetic analysis techniques and ways of modeling evolutionary change. Results suggest that components of display structure have evolved together and that the correlated evolution of display structural components has had a greater impact on the evolution of Sceloporus push-up displays than relationships between evolutionary changes in display structure and body size or display structure and microhabitat use. Increases in the complexity or communicative flexibility of Sceloporus push-up displays have been attained through altering the shape or type of head bob produced and the number of head bobs. A negative correlation between the two types of variation suggests that there is a limit or optimal length to these displays.