Photoperiodic effects on the male gonads of the Namibian gerbil, Gerbilliscus cf. leucogaster from central Namibia

Photoperiodism has been shown to be an important synchronizer of seasonal reproduction in many rodent species in the wild; it is a reliable cue as in the southern hemisphere it coincides with the onset of rainfall and hence the availability of food resources for maximal reproductive success. The photoperiodic effect on the reproductive status of the Namibian gerbil, Gerbilliscus cf. leucogaster from central Namibia was investigated. Twenty adult males were exposed to a long-day length (16L:8D), while further 20 adult males were subjected to a short-day length (SD:8L:16D); all for a period of 3 months. Testicular mass per gram body mass, testicular volume and seminiferous tubule diameters were used to assess the effect of photoperiod on gonadal development. Body mass did not significantly differ between the two photoperiodic regimes. The testicular mass per gram of body mass was significantly heavier for the males maintained on a long photoperiod compared to those on a short photoperiod. Similarly, testicular volume and seminiferous tubule diameter were greater in males maintained on a long-day cycle compared to those on the short-day cycle. These findings suggest that G. cf. leucogaster is photoresponsive to day length changes. Photoperiodic changes in the semi-arid habitats can be used to herald the onset of reproduction as it often acts in concert with other proximate cues in desert rodents, but is a constant environmental cue that does not change from year to year, unlike rainfall patterns.