Meeting Abstract
P1.138 Friday, Jan. 4 Interaction between HPA and HPG axes in two rapidly diverging Oregon Junco (Junco hyemalis thurberi) populations. ABOLINS-ABOLS, M*; KETTERSON, E D; Indiana University; Indiana University mabolins@indiana.edu
How life histories evolve depends upon complex interactions among multiple traits that vary in their degree of interdependence. Two of the most important physiological systems across vertebrate taxa are the hypothalamic-pituitary-gonadal (HPG) axis, which regulates reproductive phenotype, and the hypothalamic-pituitary-adrenal (HPA) axis, which regulates metabolism and the stress response. The two axes have been shown to be mutually inhibitory, potentially giving rise to a fundamental physiological constraint as manifested in the evolution of slow and fast life histories. However, some comparative studies of animal physiology contradict the inhibitory relationship between the HPA and HPG axes and point to independent evolution of both axes. For example, blood levels of corticosterone and testosterone (T), the end products of HPA and HPG function, are positively, not negatively, correlated in two recently diverged populations of the Oregon Junco (Junco hyemalis thurberi) in southern California. We compared the direction and strength of the interaction between the HPA and HPG axes in individuals and populations by injecting wild birds with corticotropin releasing hormone (CRH), a major activator of the HPA axis, followed by an injection of gonadotropin releasing hormone (GnRH), a major activator of the HPG axis. We predicted that if the HPA axis inhibits the HPG axis, then CRH injection should suppress a rise in T after GnRH injection compared to animals injected with saline. Alternatively, if the axes function more independently, then a rise in T should be independent of whether animals received a CRH injection. We will describe individual- and population-level sensitivity of the HPA axis, as well as the interaction between HPA and HPG axes in these two populations.
