The biology of reproduction of the Tete veld rat, Aethomys ineptus and the Namaqua rock mouse, Aethomys namaquensis (Rodentia: Muridae)

Abstract

The distributional range of the Tete veld rat, Aethomys ineptus, extends from the Limpopo Province in the north through to the south of KwaZulu Natal. The Tete veld rat is a seasonal breeder, with the breeding period confmed to the wet summer months of the year in the Gauteng Province of South Africa. The seasonality of reproduction in the Tete veld rat is confirmed by reproductive tract morphometrics, ovarian histology, plasma progesterone, and oestradiol-17β in females, and testicular histology and plasma testosterone concentrations in males. The presence of some spermatogenic activity and spermatozoa in the epididymides, as well as some follicular activity and raised circulating progesterone, and oestradiol-17β concentrations in some females during winter intimates that the Tete veld rat is possibly an opportunistic breeder. Reproduction during winter is presumably restricted by food availability and adverse winter conditions. The Namaqua rock mouse, Aethomys Namaquensis, on the other hand is widely distributed in the southern African subregion. Reproductive tract morphometrics, ovarian histology, plasma progesterone and oestradiol-17β in females, and testicular histology, seminiferous tubule diameters and plasma testosterone concentrations in males confirm that the Namaqua rock mouse is a strictly seasonal breeder. The breeding period starts in October and extends to the end of February. The absence of Graafian follicles, corpora lutea, corpora albicans, corpus hemorrhagicum, lower plasma progesterone and oestradiol concentrations in females, and small seminiferous tubule diameters, and lower testosterone concentrations during winter months suggest that reproduction is completely inhibited during this period of the year. Photoperiodic responsiveness was determined in both the Tete veld rat and the Namaqua rock mouse by exposing the animals to long day (LD) and short day (SD) lengths. Testicular mass expressed against body mass, testicular volume, and seminiferous tubule diameters were significantly larger and plasma testosterone concentrations were significantly higher in males subjected to a long day photoperiod than in males exposed to a short day. These fmdings suggest that both species are photoperiodically responsive and that photoperiod could potentially play a role in reproduction in both the Tete veld rat and the Namaqua rock mouse. In conclusion, the results in this study suggest that the Tete veld rat is a seasonal breeder with the breeding period confined to the rainy summer months in South Africa. The breeding season starts in October and extends to April. Reproduction in the Tete veld rat appears to involve photoperiod. The Namaqua rock mouse is a strictly seasonal breeder with a breeding period occurring between October and the end of February. Breeding during the winter months is completely inhibited. The Namaqua rock mouse may also utilize photoperiod to initiate reproductive events.