The male reproductive cycle of three species of Australian vespertilionid bat

Abstract

The male reproductive cycles of three species of vespertilionid bat (Nyctophilus geoffroyi, N. major and Vespadelus regulus) are described. Descriptions are based on the degree of testicular and cauda epididymal development estimated from field captures, and for N. geoffroyi, on histological examination of fixed specimens and assays of their testicular testosterone concentrations. All species were found to undergo a dissociated pattern of reproduction; the activity of the testes and accessory glands of reproduction were asynchronous. Spermatogenesis occurred in summer/early autumn (December–March) and testes generally regressed before mating began in autumn (March–May). Spermatozoa were stored in the cauda epididymides during the mating period. Leydig cells of N. geoffroyi involuted prior to mating but the prostate gland remained enlarged and secretory during winter (June–August), regressing in late spring (November). Testicular testosterone concentrations were greatest when Leydig cells were maximally enlarged, and concentrations were low during the mating period. The reproductive cycle of all species apparently involved asynchrony between primary and secondary sexual function, which is typical of vespertilionid bats inhabiting temperate latitudes. As mating occurs when sperm stores cannot be replenished, selection for prudent sperm allocation may be expected.