Meeting Abstract
Hormones fulfil a dual role in integrating changes that occur in the external with those of the internal environment to promote appropriate behavioral responses. While the role of hormones in mediating behavior has been studied in a variety of taxa, many questions on the evolution of such physiological systems remain unanswered. For example, one major question is: to what extend is hormonal variation among individuals due to genetic contributions, i.e., is a hormonal phenotype heritable and evolves through selection, or is it primarily the result of current environmental conditions? Diverse approaches, such as using selection lines, natural variation, and phenotypic engineering, can elucidate hormone, behavior, and fitness relationships. In our free-living population of great tits, Parus major, corticosterone levels are related to food availability and influence reproductive decisions. Moreover, experimentally elevated corticosterone levels before breeding increased parental effort. Therefore, it appears that corticosterone levels are regulated prior to breeding to mediate reproductive effort and regulated during breeding by parental workload. Highly plastic endocrine traits play a central role in allowing organisms to respond rapidly to environmental change; yet, not all individuals display the same degree of plasticity in these traits. I find significant individual variation in corticosterone levels in response to repeated food restriction, but the degree of plasticity is not related to oxidative costs. These results from exploring the causal and natural variation of hormone-behavior-fitness trait relationships are promising. Once we uncouple behavior and hormone cascades in relation to fitness measures, we can begin to uncover how the endocrine control system constrain and facilitate response to natural selection.
