Sexual selection and the chemical signal design of lacertid lizards

Animal signals can differ considerably in complexity and composition, even among closely related species. Work on vocal and visual signals has revealed how sexual selection can elaborate signals relevant in mate choice or rival assessment, but few studies have investigated this process in chemical signals. In this study, we correlated chemical signalling diversity and richness with degree of sexual dimorphism in a data set of 60 species of the lizard family Lacertidae. The femoral glands of male lacertid lizards exude waxy secretions, of which the lipophilic fraction is known to function in chemical communication. We determined the composition of the gland secretions using gas chromatography–mass spectrometry and calculated the chemical richness (total number of compounds) and the chemical diversity (Shannon–Wiener H’) for each species. We used sexual dimorphism in size, in shape, and a combination of both, as proxies for the intensity of sexual selection acting on each species. Although our data revealed considerable interspecific variation in the composition and complexity of the chemical signals, as well as in sexual dimorphism, we found no evidence for the idea that more elaborate signals arise through intensified sexual selection. We offer a number of conceptual and methodological explanations for this unexpected finding.