Steroid hormones secreted by the ovaries and testes are important in modulating several of the effects of photoperiod on non-reproductive as well as reproductive parameters. For example, when exposed to short day lengths hamsters typically molt and develop a winter pelage. The molt generally is accompanied by regression of the gonads and reduction of steroid hormone levels. Therefore, we will sometimes use gonadectomized hamsters with or without steroid hormone replacement to examine more closely the involvement of these hormones in seasonal changes. Describe the rationale for using animal subjects.
Siberian hamsters are excellent animals for use in studies of photoperiodism and seasonal rhythms.
Siberian hamsters are easy to maintain and breed in the laboratory and have proved to be relatively hardy and disease-resistant. Studies of the physiological basis of photoperiodism in mammals have already contributed to the development of methods that are being used for improved husbandry of livestock and for more intelligent husbandry of some endangered species. Knowledge in this area has also provided a basis from which to evaluate the extent to which day length may be an important seasonal cue for humans and whether humans exhibit seasonal rhythms. The final word is not yet in regarding human seasonality, but studies are currently in progress, and the approaches that are being used rely heavily on information from animal studies. This research has not been done previously.