The Reproductive Cycle in Male Noctule Bats, Nyctalus Noctula

Summary. Spermatogenesis took place in noctule bats during summer; spermatozoa were released from the testis in August and September, and the testes then involuted. Although no more spermatozoa were produced, they continued to be stored in the cauda epididymidis for the duration of winter. The testosterone content of the testes rose with the progress of spermatogenesis from 10 ng/pair in May to 847 ng/pair in August. The concentration of the hormone in the blood plasma paralleled this increase, rising from 4·7 ng/ml to 134 ng/ml over the same period. Testosterone levels were maintained during autumn, when most mating took place, but decreased during the subsequent winter period of sperm storage. The weights of the accessory glands and their fructose content were maintained over this period. It appears that the maintenance of active accessory glands of reproduction and of fertile spermatozoa in the epididymis has a comparatively low androgen requirement in noctule bats.