Endocrine correlates of hibernation-independent gonadal recrudescence and the limited late-winter breeding season in woodchucks, Marmota monax.
Woodchucks (Marmota monax) normally experience gonadal recrudescence towards the end of a 4-5 month hibernation, emerge in late winter, immediately breed in a short 3-week breeding season, and have regressed gonads before the next hibernation. Our studies of wild and captive animals show that fertile females give birth to single litters after a 32-day gestation and their breeding season is terminated by a reactivation of the corpora lutea of pregnancy for 1-3 months immediately postpartum. In nonbred females the breeding season is likewise terminated by spontaneous luteinization of the ovaries for 1-3 months shortly after the vernal equinox. Tests regress and testosterone declines during and after the breeding season. Circannual reproductive cycles persist in the absence of hibernation and are shortened to 9-10 months after 3-5 years of a 12L:12D photoperiod. Unique aspects of this species that merit endocrine investigation include descent/retraction of testes, transient luteolysis at parturition, superactivation of postpartum corpora lutea, regulation of the pituitary-gonadal axis by an annual endogenous metabolic cycle entrained to the annual change in photoperiod, and the hormonal basis of hibernation.
Concannon
P W
PW
Department of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853.
Baldwin
B
B
Roberts
P
P
Tennant
B
B
D000822:Animal Husbandry; D000818:Animals; D001947:Breeding; D004702:Endocrine Glands / Q000502:physiology*; D005260:Female; D006066:Gonads / Q000502:physiology*; D006605:Hibernation / Q000502:physiology*; D008297:Male; D008392:Marmota / Q000502:physiology*; D012098:Reproduction / Q000502:physiology*; D012589:Sciuridae / Q000502:physiology*; D012621:Seasons