SKELLY, S. L.; JOHN-ALDER, H. B.; Rutgers University: Effects of testosterone on growth and behavior of the eastern fence lizards, Sceloporus undulatus.

Sexual size dimorphism in Sceloporus undulatus results from a higher pre-maturational growth rate in females than in males. To gain insight into potential mechanisms of sex differences in growth, we studied behavior of free-ranging juveniles, and we experimentally investigated whether testosterone (T) influences growth and behavior. Focal observations indicated that free-ranging juvenile males are more likely to perform �broadcast� displays than females and that this was a result of a steady increase in the display rate of males throughout the active season. Males also increased their home-range use in comparison to females, such that by August males moved 1.7x further than females. In the experimental study, castrated males treated with exogenous T were more active and grew more slowly than females, intact males and castrated males. In addition, T-implanted males were infected with the greatest number of ectoparasites upon recapture. In the laboratory, feeding rates did not differ among the four groups. These findings suggest an energy allocation trade-off between growth and behavior and indicate that this trade-off can be influenced by testosterone. Supported by NSF IBN 0135167.