Abstract:
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.
