Manipulating testosterone to assess links between behavior, morphology, and performance in the Brown Anole Anolis sagrei.

Abstract Survival and reproductive success are determined by the complex interplay between behavior, physiology, morphology, and performance. When optimal trait combinations along these various phenotypic axes differ between sexes or across seasons, regulatory mechanisms such as sex steroids can often facilitate sex-specific and/or seasonal trait expression. In this study, we used surgical castration and replacement of exogenous testosterone in adult male brown anoles (Anolis sagrei) to simultaneously examine the effects of testosterone on a suite of morphological (dewlap area, body size), physiological (immune function), behavioral (dewlap, head bob, and push-up displays), and performance (stamina, sprint speed, bite force) traits. We show that testosterone increases (or castration reduces) growth rate, dewlap area, and bite force. Treatment effects on bite force may simply reflect underlying treatment differences in growth combined with allometry of bite force. Other traits, such as stamina, sprint speed, and rate of behavioral displays, were largely independent of circulating testosterone levels. Although we did not observe significant treatment effects on immune function, we found negative correlations between growth and immune function consistent with the hypothesis that testosterone mediates trade-offs between these competing aspects of energy allocation. Overall, our results demonstrate that testosterone can exert pleiotropic effects on a variety of morphological, physiological, behavioral, and performance traits that are known to influence survival and reproductive success.