[Relations between hibernation and the resumption of endocrine, testicular and thyroid activities, in Vipera aspis L. (Reptilia, Viperidae)].

The relationships between the end of hibernation and testicular and thyroid endocrine recrudescence were tested in Vipera aspis by subjecting hibernating vipers to experimental climatic conditions. Vipers kept under artificially warmed conditions (for 3.5 hr during the day to a thermal gradient from 11 to 27 degrees) 1 month before emergence showed an increase in plasma testosterone before vipers exposed to natural conditions (outdoor enclosures) did. The use of different photoperiodic conditions, long, LD 12:12, and short, LD 8:16, shows that photoperiod length has no effect on this increase. For vipers kept under prolonged hibernation (under a uniform temperature of 5 degrees or exposed to natural conditions at the northern limit of the species' distribution), testicular endocrine recrudescence was observed as soon as the first emergence only for the vipers placed at the northern range limit. Whatever the conditions, experimental or natural, the emergence of vipers always corresponds to a weight loss correlated with the increase of plasma thyroxine level. The relationship between the end of hibernation and testicular and thyroid endocrine recrudescence is discussed.