SEASONAL CHANGES IN THE OVARY OF THE BLIND MOLE RAT (SPALAX EHRENBERGI)

ABSTRACT

The present study is the first to examine closely the ovary of the blind mole rat (Spalax ehrenbergi), a solitary, highly aggressive subterranean rodent. It provides basic data on the female reproductive biology which should assist in the notoriously difficult attempts to breed this unique species. Although the mole rat is considered a seasonal breeder, large antral follicles were found to be present in the ovary throughout the year. Constant darkness and high temperatures simulating the natural burrow environment in the summer did not cause the ovary to regress. This was evident from the surprising abundance of large antral follicles, some even in the preovulatory state. Because injection of human chorionic gonadotropin (hCG) during the summer induces ovulation of these follicles, it would appear that mole rats are potentially able to reproduce outside of the known winter breeding season. The present work further strengthens previous assumptions (based on vaginal smears) that the mole rat is a reflex ovulator: first, preovulatory follicles are always present in the ovary during the winter breeding season; and second, injection of 50 i.u. hCG to randomly selected females resulted in ovulation in 67% of the females. Although at the time of copulation ovaries contained large preovulatory follicles, following copulation ovulation did not occur and pregnancy did not ensue. This suggests that copulatory stimulation by the male did not reach the ovulatory threshold. An injection of hCG immediately after sperm transfer might overcome this obstacle in future breeding attempts.