Seasonal changes in the gonads and accessory reproductive organs of the vole ( Microtus agrestis)

Abstract

Gonads and accessory reproductive organs of 161 voles ( Microtus agrestis) caught in summer and winter have been studied. The large summer testes produced abundant sperm and had conspicuous interstitial cells. In the small winter testes the epithelium of seminiferous tubules was composed chiefly of Sertoli cells and spermatogonia. Interstitial cells were generally inconspicuous in winter males. All summer females were pregnant or lactating. Summer ovaries possessed fresh corpora lutea as well as Graafian follicles. Some winter ovaries had Graafian follicles, but none had fresh corpora lutea. Seminal vesicles and ventral prostates weighed much less in winter than in summer. However, the ventral prostatic epithelium remained in winter almost as high as in summer glands. Winter males and females were divisible into 2 classes, consisting of those animals which did and did not become sexually mature in the previous summer. Voles in one winter were far more developed sexually than in others. There were also differences in the reproductive state of males in two successive summers. No obvious climatic differences could explain this variation.