Seasonal reproduction in the eastern rock elephant-shrew : influenced by rainfall and ambient temperature?

12 Dec 2012

Because environmental conditions vary seasonally in most regions, many small mammals reproduce at a specific time of the year to maximize their reproductive success. In the tropics and subtropics, the breeding season is usually determined by the extent of the dry and rainy seasons. We investigated the seasonality of reproduction in the eastern rock elephant-shrew (Elephantulus myurus), over a 12-month period and attempted to elucidate the factors that may influence seasonal reproduction in this endemic African mammal. E. myurus breeds seasonally during the warm and wet spring and summer months and cessation of breeding occurs during the cold and dry winter months of the southern hemisphere. Pregnant females were only collected from August through to January. Ovarian size and plasma progesterone started to increase a few months prior to the first rains, were highest in October and decreased thereafter. Follicular growth and corpora body numbers corresponded to this seasonal reproductive pattern. Testes and seminiferous tubule size and plasma testosterone concentration has already started to increase during the coldest months, 2 months prior to reproductive onset in females. We propose that seasonal reproduction evolved in E. myurus because of seasonally changing food availability brought about by severe seasonal changes in rainfall and ambient temperature. The direct effects of rainfall and ambient temperature on reproduction of E. myurus are ambiguous, and we discuss other environmental factors that may trigger reproductive onset in this species.