Evidence of recent population bottlenecks and inbreeding in British populations of Bechstein's bat, Myotis bechsteinii

We investigated the population genetics of seven maternity roosts of Bechstein's bats widely distributed across the south of England. Across all of the populations sampled, two mitochondrial DNA microsatellite loci were fixed for single haplotypes. Genetic diversity across eight nuclear microsatellite loci was similar in all seven populations, with a mean He of 0.727. However, six of the populations showed substantial homozygote excess, with F IS estimates greater than zero, indicative of recent inbreeding. Bottleneck tests also implied that six of the populations have experienced recent declines. Genetic differentiation among the populations was low, with a mean intersite F ST estimate of 0.041. There was no significant isolation by distance using allele frequency-based criteria (F ST and genetic distances), however, a weak correlation was found using the allele size-based R ST criterion. Assignment tests were unable to distinguish the seven sampling sites as distinct clusters. Mean intra-roost relatedness (r) was 0.079, indicative of recent inbreeding relative to German populations. All but one of the bats had one or more half or full siblings in its maternity roost. In addition, family relationships of individuals within a colony were significantly commoner than family relationships among four proximal roosts <8 km apart. The results are discussed in the context of conservation requirements for this rare British bat.