Effects of Day Length, Temperature, and Green Food on Testicular Development in a Desert Pocket Mouse Perognathus formosus

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Abstract
Coordination of reproductive condition in male pocket mice (Perognathus formosus) by environmental factors limits the season of reproduction to a time associated with the springtime peak in availability of dietary resources that are critical to reproduction. This optimal time for reproduction follows winter hibernation and precedes summer drought. Responsiveness of reproductive function to environmental influences was studied in male P. formosus of the Mojave Desert region by bringing freshly captured animals into the laboratory at different seasons and exposing them to a variety of experimental manipulations. Long days (16 h light/day) stimulated or maintained seasonal testicular function, whereas short days (8 h light/day) were nonstimulatory or inhibitory. However, because natural reproductive development begins while the mice hibernate underground in total darkness, it is not yet clear how day length might influence this pattern of reproductive development in nature. Reproductive development was greater at 13 C than at 23 C, which was in turn greater than at 33 C. This inverse relationship between temperature and reproductive maturation is a reversal of the response typical of other rodent species, and the way in which temperature affects reproductive maturation of P. formosus in nature is also not clear. If photoperiod plays a role in the winter development of the testes, it may operate prior to the onset of hibernation, whereas temperature may influence reproductive maturation during hibernation. Although P. formosus gains body mass on a diet of dry seeds without water or succulent food, its testicular development is strongly inhibited on this diet. Fresh lettuce, provided to the animals in most of the experiments, serves as an important source of water and perhaps other nutritional elements.