WALKER, B.G.*; MATT, K.S.; Gonzaga University, Spokane, WA; Arizona State University, Tempe: Baseline and stress induced corticosterone levels in female and male Siberian hamsters depends on pairing type and parental status

The Siberian hamster, Phodopus sungorus, forms loose monogamous pairs during breeding. However, it appears that females provide the majority of the parental care � as observed in both nature and captivity. Here we show how baseline and stress-induced corticosterone levels in Siberian hamsters change after pairing and giving birth. When both male and female hamsters were housed in same sex pairs (prior to breeding initiation) baseline corticosterone levels were low, and only moderate increases in corticosterone were observed after a capture stress protocol. After being moved to mixed-sex pairs and allowed to interact for 7 days (i.e., attempt matings), in females, both baseline corticosterone and the magnitude of the corticosterone stress response increased significantly as compared to previous same-sex housing levels. In contrast, baseline levels in males remained similar as when paired with other males, although the stress response increased considerably. Finally, after raising pups for 7 days, baseline corticosterone remained high in females, but a capture stress elicited no further increase in corticosterone. In males, baselines were lower than in females, but capture stress levels similarly showed no significant increases. It was not surprising that female hamsters, chief care-givers in the nest, showed elevated baseline corticosterone as energetic demands increased due to raising young. Similarly, their blunted stress response is a likely mechanism to avoid the high reproductive cost of a flight response when young are present. For males that provide little parental care, the only strong modification of corticosterone was elicited during they period they were actively devoting energy towards mating.