Meeting Abstract

53.5  Saturday, Jan. 5  Seasonal differences in the reproductive endocrinology of two recently-diverged songbird (Junco hyemalis) populations following a unique colonization event ATWELL, J.W.*; CARDOSO, G.C.; KETTERSON, E.K.; Indiana Univ.; Univ. of Chicago; Indiana Univ. jwatwell@indiana.edu

In variable environments, selection is expected to favor endocrine mechanisms that efficiently coordinate seasonal physiology and behavior to maximize breeding success. However, few studies have evaluated the importance of the proximate mechanisms that are predicted to underlie adaptive changes in breeding phenology. This is because such studies require a documented evolutionary history as well as an understanding of the adaptive value of changes in breeding phenology. In this study, we utilize a unique colonization event to ask whether or not the adaptive changes in breeding season length exhibited by a recently-colonized, urban population of dark-eyed juncos (Junco hyemalis) are correlated with seasonal differences in the functioning of the endocrine hypothalamic-pituitary-gonadal (HPG) axis. We compare reproductive morphology, plasma testosterone [T] levels (both basal T and T in response to a challenge of gonadotropin-releasing hormone [GnRH]), and breeding phenology in the coastal, colonist population and a nearby montane population breeding in the native range. Our initial results indicate that despite inhabiting identical latitudes and having diverged very recently (<30yrs), males of our two study populations exhibit divergent seasonal HPG physiologies that correlate with inter-population differences in the onset and termination of breeding. Our ongoing studies are examining HPG seasonality in females and addressing whether the observed inter-population differences in HPG seasonality represent plastic changes and/or genetic adaptations to the novel environment.