The reproductive cycle of 108 mature male beach voles, Microtus breweri, endemic to Muskeget Island, Massachusetts, was investigated. Changes in body weight were seen through the year with animals heaviest (62.10 ± 1.38 g) in April and lightest (43.40 ± 2.84 g) in October. In April through June spermatogenic activity was maximum while testicular weight was greatest (1300 -1600 mg). In July spermatogenic activity remained maximum although testicular weight dropped (858.72 ± 152.00 mg). A decline in spermatogenic activity and testicular size followed during August through October. Testes were quiescent and weished approximately 300 mg from October through December. Plasma androgen levels were highest (>2 ng/ml) during spermatogenic activity in April through June and lowest (<1.0 ng/ml) in October when the testes contained only spermatogonia and Sertoli cells. The reinitiation of spermatogenesis in the male beach voles on Muskeget Island is synchronized with the spring increase in photoperiod and temperature, and testicular regression begins during the late summer. © 1980.
Adams, M. R., Tamarin, R. H., & Callard, I. P. (1980). Seasonal changes in plasma androgen levels and the gonads of the beach vole, Microtus breweri. General and Comparative Endocrinology, 41(1), 31–40. https://doi.org/10.1016/0016-6480(80)90029-5