Meeting Abstract
Sexual size dimorphism (SSD) is typically associated with a balance between sexual selection through male-male competition and natural selection through female fecundity benefits. In species where females and males make different uses of their habitat, SSD can also be due to sex-specific ecological adaptations to the environment. The evolutionary drivers of sexual dimorphism are unfortunately often assumed to reproductive in nature, and the relationship between sexual dimorphism and ecological adaptations is rarely explored. Here, we test the hypothesis that sexual size dimorphism in the lizard Uta stansburiana is at least partially driven by ecological adaptations. Populations of this polymorphic lizard differ in number of males color morphs, as well as in degree of SSD. By collecting morphological and ecological data on males and females from 14 populations of U. stansburiana distributed across the southwestern US, we show that environmental factors influence female and male size differently, resulting in intraspecific differences in the degrees of SSD. By building a population-level phylogeny of this species, we have also shown that although genetic similarities explain some of the variation observed between populations, a proportion of the variance encountered is better explained by environmental conditions than by number of male morphs or by phylogenetic relationships alone. Our results highlight that natural selection through ecological adaptations are a long-ignored potential driver of sexual dimorphism in a classic study system of sexual selection, and urge future studies to go beyond the relationship between sexual dimorphism and reproductive benefits.
