Sexual Segregation and Flexible Mating Patterns in Temperate Bats

Roger K. Butlin,Brock Fenton,Ruth L. Angell,John D. Altringham

doi:10.1371/journal.pone.0054194

Roger K. Butlin, Brock Fenton + Show 2 more

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https://doi.org/10.1371/journal.pone.0054194

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Journal: PLoS ONE	Publication Date: Jan 24, 2013
Citations: 46	License type: CC BY 4.0

Affiliation: University of Sheffield, University of Leeds

Abstract

Social structure evolves from a trade-off between the costs and benefits of group-living, which are in turn dependent upon the distribution of key resources such as food and shelter. Males and females, or juveniles and adults, may have different priorities when selecting habitat due to differences in physiological or behavioural imperatives, leading to complex patterns in group composition. We studied social structure and mating behaviour in the insectivorous bat Myotis daubentonii along an altitudinal gradient, combining field studies with molecular genetics. With increasing altitude the proportion of males in summer roosts increased and only males were present in the highest roosts. With increasing altitude environmental temperature decreased, nightly variation in temperature increased, and bat foraging activity decreased, supporting the hypothesis that the harsher, high elevation sites cannot support breeding females. We found that offspring in female-dominated lowland roosts had a very high probability of being fathered by bats caught during autumn swarming at hibernation sites, in contrast to those in intermediate roosts, which had a high probability of being fathered by males sharing the nursery roost with the females. Whilst females normally appear to exclude males from nursery colonies, for those in marginal habitats, one explanation for the presence of males is that the thermoregulatory benefits to the females may outweigh disadvantages, such as competition for food, and give some males an opportunity to increase their breeding success. We suggest that the environment, and its effects on resource distribution, thus determine social structure, which in turn determines the mating pattern that has evolved.

Highlights

Social structure evolves from a trade-off between the costs and benefits of group-living, which are in turn dependent upon the distribution of key resources such as food and shelter
Senior et al [4] showed that sexual segregation in the bat Myotis daubentonii along an altitudinal gradient led to segregation among groups of males
To address the three questions posed above, we extended the study downstream of the sites studied by Senior et al [4], investigating the changing patterns of roost composition, social structure and paternity, in relation to environment

Summary

Introduction

Social structure evolves from a trade-off between the costs and benefits of group-living, which are in turn dependent upon the distribution of key resources such as food and shelter. At mid elevations males shared nursery roosts with females and had a much greater chance of fathering offspring from these roosts than the males at higher elevations. These males were presumed, on the balance of evidence, to exclude other males from habitat and roosts occupied by females. The excluded males were, able to mate during autumn swarming, but with a much lower probability of fathering the young from mid elevation roosts. Swarming occurs during the typically brief visits bats make to hibernation sites in late summer and autumn to mate. As the swarming season progresses into hibernation an increasing proportion of the visiting bats, of both sexes, remain in the hibernation sites e.g. As the swarming season progresses into hibernation an increasing proportion of the visiting bats, of both sexes, remain in the hibernation sites e.g. [5][6]

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