Meeting Abstract

59.10  Wednesday, Jan. 6  Corticosterone as a mediator of reproductive effort PATTERSON, S.H.*; BREUNER, C.W.; Univ. of Montana; Univ. of Montana stephen1.patterson@umontana.edu

Reproductive effort varies among individuals and can have a profound effect on fitness. The physiological mechanisms underlying this variation are important to understanding inter-individual differences in reproductive effort and, by extension, fitness. Individuals with access to greater energetic resources tend to invest more in reproduction and also tend to have lower levels of corticosterone (a “stress” hormone involved in energy regulation and behavior modulation). This relationship between energetic resources / reproductive effort and corticosterone leads to the plausible hypothesis that corticosterone functions as a physiological mechanism linking resource availability and reproductive effort. However, experimental evidence for this connection is lacking. In this study, we manipulated energetic resources and plasma corticosterone concentrations in female Tree Swallows (Tachycineta bicolor), aerial foraging insectivores. We also measured offspring feeding rates as a proxy for reproductive effort. We manipulated energetic resources by clipping 3 primary feathers per wing to reduce foraging and locomotor efficiency. We manipulated corticosterone levels using corticosterone-soaked dermal patches. Analysis is ongoing, and results will be discussed in the framework of physiological mechanisms of reproductive effort decisions.