Sexual selection is a powerful force for diversification because it can shape morphology, strongly influence behavior, speed up rates of evolutionary change, and promote speciation. A fundamental question is how to link the strong levels of sexual selection acting upon traits within populations to the diversification of body form and behavior among species. I tackled this problem by studying variation among populations of Uta stansburiana in sexual size dimorphism (a trait that can be strongly influenced by sexual selection) and whether changes in sexual dimorphism were associated with the loss of the mating strategy polymorphism. I discovered that all polymorphic populations had male-biased sexual size dimorphism (picture on the left) while some monomorphic populations had no sexual dimorphism (picture on the right) or female-biased sexual dimorphism. Phylogenetic tests suggested that the mode of selection on sexual dimorphism has changed between monomorphic and polymorphic populations. Variation in sexual dimorphism among populations polymorphic for multiple male morphs was associated with changes in male size, which suggested that male-male competition shapes size dimorphism in these populations. In contrast, changes to sexual dimorphism in monomorphic populations were correlated with changes in female size and clutch size, which suggests that selection on female fecundity has altered size in these populations. This study showed that multiple selective forces are likely to shape sexual dimorphism within a species and that shifts in levels of polymorphism can have large effects on trait evolution.
Publications
Corl, A., A. R. Davis, S. R. Kuchta, T. Comendant, and B. Sinervo. 2010. Alternative mating strategies and the evolution of sexual size dimorphism in the side-blotched lizard, Uta stansburiana: a population-level comparative analysis. Evolution. 64: 79-96. [link]
