Mating patterns, relatedness and the basis of natal philopatry in the brown long-eared bat, Plecotus auritus

The brown long-eared bat, Plecotus auritus, is unusual among temperate zone bats in that summer maternity colonies are composed of adult males and fem ales, with both sexes displaying natal philopatry and long-term association with a colony. Here, we describe the use of microsatellite analysis to inv estigate colony relatedness and mating patterns, with the aim of identifyin g the evolutionary determinants of social organization in P. auritus. Mean colony relatedness was found to be low (R = 0.033 +/- 0.002), with pairwise estimates of R within colonies ranging from -0.4 to 0.9. The proportion of young fathered by males in their own colony was investigated using a Bayes ian approach, incorporating parameters detailing the number of untyped indi viduals. This analysis revealed that most offspring were fathered by males originating from a different colony to their own. In addition, we determine d that the number of paternal half-sibs among cohorts of young was low, inf erring little or no skew in male reproductive success. The results of this study suggest that kin selection cannot account for colony stability and na tal philopatry in P. auritus, which may instead be explained by advantages accrued through the use of familiar and successful roost sites, and through long-term associations with conspecifics. Moreover, because the underlying causes of male natal dispersal in mammals, such as risk of inbreeding or c ompetition for mates, appear to be avoided via extra-colony copulation and low male reproductive skew, both P. auritus males and females are able to b enefit from long-term association with the natal colony.