Evolution of litter size in bats and its influence on longevity and roosting ecology

Abstract

Litter size varies in mammals, with about half of the species producing at least two offspring per gestation (polytocy). In bats, however, the modal litter size is one (monotocy), and polytocy is restricted to family Vespertilionidae. Here, we reconstruct the evolutionary history of polytocy in chiropterans and use phylogenetically informed regressions to investigate its relationship to roost type, longevity and group size. Our phylogenetic reconstructions suggested that production of multiple offspring was the ancestral condition in family Vespertilionidae. The distribution of monotocy/polytocy in Chiroptera was best explained by a minimum of two evolutionary transitions from monotocy to polytocy and by ≥ 18 transitions from polytocy to monotocy. The regression models showed that longevity and roost type explained the variation in litter size, whereas group size did not. Our analyses also revealed a greater diversity of polytocous bats in the Northern Hemisphere, in both temperate and tropical regions. We suggest that the high resource allocation to reproduction in polytocous bats limited their lifespan. The absence of a relationship between polytocy and group size indicates that the benefits of cooperative breeding surpass the costs of intrasexual competition in bats.