Meeting Abstract

P2.25  Wednesday, Jan. 5  Effect of testosterone on the synchronization of activity rhythms to low amplutide zeitgebers in an arctic-breeding songbird. SALLI, B.M.*; ASHLEY, N.T.; BUCK, C.L.; Dept. of Biological Sciences, Univ. of Alaska, Anchorage, Alaska, USA bmsalli@uaa.alaska.edu

A key feature of polar environments is the continual presence of the sun above the horizon throughout most of the summer. During this time, many arctic animals, such as caribou (Rangifer tarandus tarandus), abandon diel rhythms of activity. However, arctic migrant birds continue to display a distinct circadian rhythm despite continuous daylight experienced on breeding grounds. It is hypothesized that the persistence of diel rhythms involves entrainment to low amplitude zeitgebers, that include small changes in light intensity or spectral quality of sunlight that occur over the polar day. We determined previously that captive, Lapland longspurs (Calcarius lapponicus), an arctic migrant songbird, failed to entrain to light regimes that mimicked daily changes in light intensity or color temperature of similar to polar-day conditions in Barrow, Alaska, (71° N), where birds were captured. Because birds were in non-breeding condition, it is possible that sensitivity to polar-day zeitgebers is increased during the breeding season and is proximately regulated by sex steroids. Here, we tested this hypothesis by administering exogenous testosterone or empty implants to non-breeding male Lapland longspurs and exposed them to the light regimes described above. Results of this study will elucidate a potential hormonal role in regulating entrainment properties within the biological clock of a high-latitude breeding species.