Hayes, T. B.: EVOLUTIONARY DEVELOPMENTAL ENDOCRINOLOGY AND BEHAVIORIAL ECOLOGY: AN INTEGRATIVE APPROACH TO UNDERSTANDING THE STRESS RESPONSE IN WESTERN TOADS (BUFO BOREAS)

We showed that exogenous corticosterone (CORT) decreased growth and development in early larval stages, but increased development and stimulated metamorphosis during later stages in the western toad (Bufo boreas). Later, we showed that endogenous CORT increased with larval density, while growth and development decreased. Furthermore, we recently showed that inhibiting CORT-synthesis with metyrapone prevented the inhibition of growth and development associated with crowding. Thus, our data support a natural role for CORT in regulating the response to crowding in this species. Here, we propose an adaptive model, in which crowded larvae in a natural population may grow and develop slower in response to increased CORT during early stages. On the contrary, older (or later-staged larvae) will accelerate development and metamorphosis in response to crowding, thereby alleviating some of the crowding stress. The adaptive significance of the model is increased if Bufo boreas shows kin recognition and preferentially schools with siblings, as shown in the literature. Kin recognition would increase inclusive fitness: Once older siblings metamorphose (alleviating crowding), then younger sibs would have the opportunity to develop faster and metamorphosis, as opposed to intense competition between all larvae. An examination of mixed versus pure sib groups could not identify a difference between these groups in their response to crowding. Thus the proposed strategy can be realized only if tadpoles truly show kin recognition and/or if adults show philopatry such that schools of mixed sibships are minimized. Supported by NSF grants IBN-9513362 and IBN-9508996.