Tracing the origins of signal diversity in anole lizards: phylogenetic approaches to inferring the evolution of complex behaviour

Within species, natural and sexual selection work together to shape the design of animal communicative systems, and sometimes act differentially on alternate components to produce a single elaborate phenotype that works well in several contexts. Here, we show a similar pattern at the interspecific level, and describe how an intricate selective regime can shape diversification of a complex behaviour across species. Using four phylogenetic comparative methods, alternative phylogenetic hypotheses, and a data set compiled from over 50 different sources representing 53 taxa, we test the relative importance of different ecological variables on the evolution of anole visual displays. Our study makes use of the inherent complexity of these signals and the availability of published descriptions in the form of display-action-patterns. Results indicate that different selective forces are linked to change in different display components. Whereas evolutionary changes in display duration appear to be linked to sexual size dimorphism, measures of display complexity (number and uniformity of display components) were more tightly associated with the need to facilitate species recognition and the type of light environment in which the display is typically performed. We also found some evidence that ecomorph distinctions, a major force in morphological evolution of anoles, have had an impact on the evolution of display structure. We use our findings to highlight areas for future research and discuss the similarities and differences between display evolution in anoles and in other lizard genera.