Meeting Abstract

18.3  Monday, Jan. 4  Seasonal and individual differences in elevation of LH and T in response to GnRH in female Dark-eyed Juncos BERGEON BURNS, C.M.*; WINGFIELD, J.C.; KETTERSON, E.D.; Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington cbergeon@indiana.edu

Evolutionary endocrinology seeks to understand how hormone-mediated traits evolve. An essential first step is to understand the basis for individual variation in circulating hormones. Our focus is the steroid hormone testosterone (T) in birds. A standardized injection of gonadotropin releasing hormone (GnRH) triggers secretion of luteinizing hormone (LH) from the pituitary, which in turn triggers a transient increase in T from the gonads. Previous study has shown that male dark-eyed juncos (Junco hyemalis) vary widely in the degree to which they elevate T after a GnRH challenge and in related behavior. While T is typically considered a ‘male hormone,’ gravid female juncos also elevate T in response to GnRH, presumably via an increase in LH. Whether T co-varies with other aspects of female phenotype remains to be seen. Also unknown are the causes of among-female variability in elevation of T in response to GnRH, i.e., how much of the variability can be attributed to variation in pituitary sensitivity to GnRH (as measured by production of LH) vs. variation in gonadal sensitivity to LH (as measured by T)? Is a strong responder to GnRH more sensitive to both GnRH and LH, or do these sensitivities vary independently? Interestingly, although females elevate T in response to GnRH only when gravid, they elevate LH in response to GnRH at other stages of reproduction. From April-July 2009, we challenged 72 free-living female juncos in the Black Hills of South Dakota with GnRH and examined patterns of LH and T across the season and stages of breeding. We will report determinants of strong and weak response to GnRH and whether strong and weak responders differ in phenotype.