Circannual changes in serum testosterone concentrations of adult and yearling woodchucks (Marmota monax) [Variations circannuelles des concentrations sériques en testostérone chez les marmottes adultes et les un-ans].

Résumé

Testicular volumes and serum testosterone concentrations were determined biweekly in 5 adult and 4 yearling woodchucks maintained indoors from December through August. Food and water were provided ad libitum except for 2 mo beginning at the winter solstice when feeding and lighting (12L:12D) supplemental to available natural light were discontinued. Temperatures fluctuated with outdoor temperatures greater than 4 degrees C. No significant hibernation occurred. Testes in adults were small in December (0.3-1.8 cm3), largest in February and March (3.5-5.6 cm3), and smallest in late June (0.1-0.5 cm3). Testosterone was basal in December (less than 0.6 ng/ml), maximal (3.4-6.6 ng/ml) between early January and late March, and minimal from April through August (less than 0.8 ng/ml). In yearlings, maximum testes volumes (1.6 cm3) and serum testosterone (0.9 +/- 0.2 ng/ml) were less, and occurred later, than in adults. Testosterone levels and testis volumes measured in newly captured woodchucks in March and April and again 2-3 mo later were generally similar to those of their laboratory counterparts. Thus, in woodchucks: annual cycles of testosterone production and of testes recrudescence and regression parallel each other with maxima during the short, late-winter breeding season those cycles are not altered significantly by the absence of hibernation or the present conditions of captivity and yearling males apparently are not an important part of the breeding population.