Seasonal Changes in the Reproductive Tract of the Male Opossum Didelphis virginiana Kerr in Florida

Abstract

Seasonal morphological and histological changes in the reproductive tract of the male opossum Didelphis virginiana Kerr in S central Florida were described on the basis of 80 adults collected from September 1969 through August 1970. An annual reproductive cycle was evident. In autumn the testes were largest, seminiferous tubules contained few small lumina, and sperm production decreased. In winter the average size of the testes decreased, the lumina of the seminiferous tubules increased and sperm were abundant. Although sperm were present in the epididymides all year, there were significant differences in the diameter of the lumina and the height of columnar epithelial cells in the tubules. The average length and width of the prostate gland, and the length of the glans penis increased significantly from autumn to winter. INTRODUCTION The seasonal reproductive cycle of female opossums Didelphis virginiana Kerr in Florida and other eastern states has been well-documented (Siegler, 1971; McKeever, 1958; Burns and Burns, 1957; Reynolds, 1952; Hartman 1928). However, the seasonal changes in the male reproductive tract during the year have received considerably less attention. The general morphology and histology of the reproductive system have been described by Robbins (1973) and Chase (1939). Biggers (1965) examined 96 opossums from Pennsylvania and concluded that males are in breeding condition all year. Fleming (1973) found no seasonal changes in reproduction in the male opossum (Didelphis marsupialis) from Panama. Hence, male opossums have been generally assumed to be in breeding condition all year. Contrary to this, when Chase (1939) examined 43 adult male opossums from Kentucky, Oklahoma, Missouri and North Carolina during autumn and winter, she found one male with no sperm in December. She made no other reference to seasonal variation of the testes, but differences in the size of the accessory glands were mentioned. In addition, Painter (1922) examined the testes of four animals and found that maturation stages were more abundant in testes preserved in January than in those from October and November. In this study I examine the testes and selected accessory glands of male opossums from S central Florida for the occurrence of seasonal changes.