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Namaqua dwarf adders must breed frequently: the problem with being small



Bryan Maritz, School of Animal, Plant, and Environmental Sciences, University of the Witwatersrand, Johannesburg, P.O. Wits, 2050, South Africa.



Reproductive frequency is a key component of reproductive output, and has important influences on organismal fitness and population persistence. Viperid snakes, like many other ectothermic vertebrates, generally exhibit a low frequency of reproduction (LFR), as females only reproduce every second year, or even less frequently. However, for small-bodied species with constrained clutch/litter sizes, and low survival, reproductive frequency cannot be too infrequent if populations are to persist. We assessed whether Bitis schneideri, a small, arid-adapted viperid snake from southern Africa has the LFR typical of many other viperids, despite having low survival and small litters. We calculated the reproductive frequency required to sustain a population using information gathered from recent studies of the ecology of the species. The small litter size imposed by being small-bodied, and low annual survival, require B. schneideri to reproduce frequently, probably annually, for populations to persist. We also assessed the reproductive status of all available preserved adult females. A high proportion were reproductive (up to 80% during summer), with developing or mature follicles, or developing young. Such frequent reproduction is atypical, even among closely related species, and might be facilitated through the capacity of B. schneideri to feed year-round in the aseasonal habitat in which it occurs. We predict that future studies of small-bodied species from climates that allow for extended periods of feeding will continue to show that frequent reproduction is more widespread among vipers than is currently assumed.

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