ABSTRACT
Like many other wild mammals, hibernators exhibit anticipatory processes to cope with the fluctuations of their external environment. When the hamsters are caught in April they have just experienced gonadal recrudescence. If exposed at that time to long photoperiod (LP) or short photoperiod (SP) conditions a true photoperiodic species should remain sexually active for as long as LP or SP conditions are maintained. Hibernation is closely linked to the level of circulating plasma testosterone since hibernation does not occur during the time the animals are sexually active and since a continuous release of the hormone through implanted silastic capsules prevents the animals entering into hibernation. But hibernation, as food intake and body weight, is also directly controlled by photoperiod since the above described events occured also in castrated animals. However at the same time, an endogenous annual rhythm in reproductive axis is evident.
