AFRICAN BATS - EVOLUTION OF REPRODUCTIVE PATTERNS AND DELAYS

Patterns of reproduction in African bats can be compared in three laxo n-based groups: fruit bats (Megachiroptera), fretailed bats (Microchir optera: Molassidae) and the nonmolossid Microchiroptera. In the fruit bats and nonmolossid Microchiroptera there is a trend from either seas onal or aseasonal polyestry, with prolonged or continuous spermatogene sis in the tropics, towards seasonal monestry and seasonal spermatogen esis at more temperate latitudes. Reproductive delays (sperm storage, delayed implantation and delayed development) are rare at tropical lat itudes, but are the norm in the nonmolassid Microchiroptera away from the tropics. The molassids are mostly polyestrous at tropical and temp erate latitudes, although the duration of the reproductive season decr eases with increasing latitude. The molassids appear to have escaped t he constraints that affect reproduction of the other Microchiroptera. We propose that this may be due to their flight capabilities and forag ing behavior, which give them access to year-round food, and to the th ermal characteristics of their roosts. We suggest that the ancestral r eproductive pattern of the Chiroptera was probably aseasonal or season al polyestry, as seen in extant tropical species, and therefore that r eproductive cycles have evolved from the polyestrous to the monestrous condition. Short periods of reproductive delay occur in some species of tropical bats; we suggest that these reproductive delays originally were not adaptations to temperate latitudes but rather to the long dr y season, which is characteristic of African tropical latitudes. With the move away from the tropics, selective pressures, acting on the tim ing of lactation and spermatogenesis, would have ensured that these pr ocesses continued to occur in the warm wet season, and that the length of the reproductive delay increased. This model accommodates the prob able evolutionary origin of bats and links the evolution and developme nt of reproductive delays to the differences in climate that occur wit h changes in latitude. There is evidence that mate choice and sperm co mpetition may be important to modern bats, but we believe that they ne ed not be invoked as causal factors in the evolution of reproductive d elays, which can be adequately explained using purely energetic argume nts.