The Allometry of Sexual Dimorphism in Sceloporus formosus (Squamata: Phrynosomatidae)

In many animal species, adult females and males often differ in characteristics other than primary sexual traits. Thus, body size tends to be related to reproductive success through different pathways in females and males, sex-specific foraging or dispersal strategies, and/or adaptations to reduce intersexual trophic competition. As result of these differences, the body size that conveys maximal fitness often differs between the sexes, favoring the evolution of sexual size dimorphism. In this study, we use an allometric approach to evaluate the changes in magnitude of sexual dimorphism in a population of Sceloporus formosus. Allometry refers to the relationships observed between body size and other organismal traits. Natural and sexual selection on morphological traits may modify allometric relationships. Traits under selection can show positive allometry, with slopes steeper than 1 (hyperallometry). We performed allometric major axis regressions of seven morphological traits on the snout–vent length, a standard measure used as a proxy for lizard size. The major axis regressions of female trunk length and width, and male trunk length showed hyperallometric slopes, suggesting that in S. formosus these traits could be under natural selection.