9318203 Stetson Research comparing the importance of the pituitary hormone prolactin (PRL) in reproduction and pledge development in golden hamsters, Siberian hamsters and collard lemmings will be initiated in the year covered by this award. These species show dramatically different physiological changes in reproduction and pelage development on a seasonal basis. While Siberian hamsters and lemmings molt to a white pelage during the winter (short day response), golden hamsters do not. While both hamster species are inhibited reproductively by short days, lemmings continue to breed vigorously, despite the winter morphology induced by these environmental conditions. In all three species, serum PRL levels are high under long days and low under short days. Since PRL influences both reproductive status and pelage characteristics, we hypothesize that the importance of PRL in these processes will differ in our 3 experimental species. Such differences may indicate specific adaptive divergences in the function of PRL; a divergence driven by the evolution of species in environments with dramatically differing selective pressures. ***
