Post-glacial colonization, latitude, isolation-by-distance, and local fragmentation have shaped the genetic diversity of common toads ( Bufo bufo ) across Britain

Abstract The evolutionary history of many species found in Britain has been shaped by a combination of postglacial colonization dynamics and more recent anthropogenic activity. Documenting genetic diversity is important for informing the overall conservation status of given species, and to aid in developing suitable conservation management strategies. In this study we present the first island-wide population genetic study of the toad Bufo bufo in Britain, using two mitochondrial and eight nuclear microsatellite markers which generated data for 823 animals. We found low genetic diversity and low levels of geographical structuring, and possible evidence of a two-wave colonization to Britain from mainland Europe in the mitochondrial loci. Our microsatellite data recovered moderate genetic structuring, with evidence of recent admixture in most sampled sites. Assigned genetic clusters were only loosely associated with geography, suggesting that genetic differentiation is driven primarily by the observed isolation-by-distance rather than discrete barriers to gene flow. Levels of allelic richness decreased significantly with higher latitude and correlated positively with census size based on counts. Other genetic diversity indices and estimates of genetic effective population sizes did not correlate with population census size proxies. Our study identified sites with high genetic distinctiveness or signs of genetic erosion, and will inform the future conservation management of B. bufo across the UK.