Failure of the Estrous Cycle and Spermatogenesis to Respond to Day Length in a Subtropical African Rodent, the Pouched Mouse (Saccostomus campestris)'

Little is known about the role of photoperiod in the control of reproduction in mammals from the tropics in general and, in particular, from the Afrotropics. The present study examined the reproductive photosensitivity of the pouched mouse (Sacco-stomus campestris: Cricetidae), a small, seasonally breeding rodent that occurs from about 120 S to 33°S in Africa. Groups of 10 laboratory-bred male pouched mice were exposed to either long-day (16L:8D) or short-day (8L:16D) conditions for 14 wk, after which they were killed and the spermatogenic activity of the testes was assessed histologically. A group of 10 adult, multiparous females were exposed to long-day conditions for 3 mo, after which the lengths of five consecutive estrous cycles were measured. Thereafter, day length was reduced to 10L:14D, and after 16 days acclimation, the lengths of five estrous cycles were measured. Finally, day length was reduced to 8L:16D, and after 33 days, the lengths of five estrous cycles were measured. Day length had no influence on body size, testis size, or the histology of the testis, and all specimens were actively producing spermatozoa. The length of the estrous cycle (4.0 0.3 days under long-day conditions) did not change significantly with the decrease in pho-toperiod. In a third experiment, 14 multiparous and six nulliparous females that had been maintained under short-day conditions for 33 days were mated and successfully reared litters. These results indicate that spermatogenesis and the estrous cycle of the pouched mouse are not inhibited by short photoperiod alone, and this is supported by the observation that females will conceive and carry litters to full term under short-day conditions. We conclude that the seasonal reproduction observed in the field is probably not controlled by photoperiod but by caloric or nutritional availability