Meeting Abstract
Sexual dimorphism is typically treated as a consequence of sex-specific reproductive benefits. Environmental factors may, however, determine or modulate the costs and benefits associated to certain phenotypes. In species distributed along steep environmental gradients, populations may differ in their degree of sexual dimorphism as a consequence of local adaptation. Western fence lizards (Sceloporus occidentalis) present great variation in size, color pattern and degree of sexual dimorphism across their distribution. This species is often infected with lizard malaria, transmitted by Plasmodium mexicanum. Malaria reduces infected males speed, aggressiveness, and territoriality, and infects disproportionately more larger and brightly colored males. Malaria may, therefore, bring a cost to large and brightly colored males, while reducing the sexual benefits associated with those traits. We aim to determine the influence of malaria on the evolution of intraspecific phenotypic variation by understanding how the spatial structure of the malaria parasite P. mexicanum relates to phenotypic variation in Western fence lizards. More specifically, we test the prediction that a population’s degree of sexual dimorphism is inversely related to the prevalence of malaria in its environment. By collecting morphological and ecological data on specimens from across California, we show that female and male phenotypes respond to environmental variables differently, resulting in intraspecific differences in degree of sexual dimorphism. We also show that the prevalence of malaria is extremely patchy, and relate it to differences in lizard morphology. Our results show that parasites may be an important mediator of sexual selection and that natural selection, through local adaptation, is a potential driver of sexual dimorphism.
