Many reintroduction projects for conservation fail, and there are a large number of factors that may contribute to failure. Genetic analysis can be used to help stack the odds of a reintroduction in favour of success, by conducting assessment of source populations to evaluate the possibility of inbreeding and outbreeding depression and by conducting postrelease monitoring. In this study, we use a panel of 306 SNP (single nucleotide polymorphism) markers and 487–489 base pairs of mitochondrial DNA control region sequence data to examine 321 individuals from possible source populations of the Eurasian beaver for a reintroduction to Scotland. We use this information to reassess the phylogenetic history of the Eurasian beavers, to examine the genetic legacy of past reintroductions on the Eurasian landmass and to assess the future power of the genetic markers to conduct ongoing monitoring via parentage analysis and individual identification. We demonstrate the capacity of medium density genetic data (hundreds of SNPs) to provide information suitable for applied conservation and discuss the difficulty of balancing the need for high genetic diversity against phylogenetic best fit when choosing source population(s) for reintroduction.

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Several larger vertebrate species have recovered from dramatic bottlenecks caused by overhunting and habitat destruction. One of the most notable comebacks concerns the Eurasian beaver (Castor fiber L.), which has increased its range by natural dispersal from both relict populations and populations established through translocations. Genetic methods have recently been used to study beavers at several locations. However, owing to a lack of reference samples from relict populations and alternative names of mitochondrial DNA haplotypes, the ancestry of re-established beaver populations remains obscure. Here, we focus on the genetic characterization of several newly established populations. Unlike previous studies, we also used microsatellite genotypes of reference samples from all relict populations. Our analysis was fully capable of tracing the origin of the nuclear and mitochondrial genome to relict populations. Although we confirmed an extraordinarily low genetic diversity in relict populations, our analysis showed restored diversity in newly established populations resulting from translocations. Recent expansions and stochastic effects have created a strong but complicated population structure, with neighbouring populations differing significantly in genetic composition. We conclude that this restored genetic diversity very likely contributes to the viability and ongoing expansion of the newly established populations.