Populations of the Lizard, Sceloporus occidentalis, that Differ in Melanization have Different Rates of Wound Healing

Mechanisms underlying production of animal coloration can affect key traits besides coloration. Melanin, and molecules regulating melanin, can directly and indirectly affect other phenotypic traits, such as immune function. We asked whether melanization and a whole-organism measure of immune function are associated with wound healing. Working with two populations of adult male western fence lizards, Sceloporus occidentalis, we compared one high-elevation and one low-elevation population in California where individuals are increasingly darker at higher elevations, measuring wound healing rates. Because of potential interactions of steroid hormones and immune function, we also measured plasma levels of testosterone and corticosterone. Mean healing rates differed significantly, with males in the darker high-elevation population healing more quickly compared to lighter low-elevation males. Males in the low-elevation population had significantly higher mean baseline steroid concentrations. These steroid hormones were also negatively associated with wound healing. We discuss potential differences in selective regime that could produce different patterns. These data also suggest that hormonal pleiotropy does not constrain phenotypic variation.