Annual Cycle of Spermatogenesis and Testis Morphology in Woodchucks

Testes of woodchucks in central Pennsylvania were examined histologically to determine effects of season and age on morphology and spermatogenic activity. Spermatogenic activity and size of the seminiferous tubules were greatest in adults at the time of emergence from hibernation in February and least during autumn. Maturation depletion and a decline in mean testes weight were evident prior to the period of reproductive activity in March. Mean testes weight declined less rapidly than did tubule size and spermatogenic activity, apparently due to an increase in interstitial tissue as tubule size dimished. Mature spermatozoa were present in testes of some yearlings at the time of emergence from hibernation. However, most males probably mature sexually at 2 years of age. During each month through May, some yearlings tended to mature sexually more than others, as evidenced by active progression and degeneration of spermatogenesis in known-age animals.