Genetic monitoring to evaluate reintroduction attempts of a highly endangered rodent

The ultimate strategy to prevent species extinction is captive breeding followed by reintroduction of individuals into the wild. Unfortunately, overall success of reintroductions is poor and in most cases conservation breeding is applied for species where individual numbers, population numbers and genetic diversity is strongly reduced. In addition, reintroductions inevitably result in small populations with poor genetic status. Systematic demographic and genetic monitoring is needed to optimize conservation actions. Here we show how genetic monitoring was useful and informative in a reintroduction project for the highly endangered Common hamster (Cricetus cricetus) in the Netherlands and Belgium. Using well defined breeding lines of original relict populations combined with a systematic reintroduction scheme including consecutive supplementations made it possible to infer success of reintroduction, supplementation and following admixture of populations. An initial loss of genetic diversity could be detected in some of the reintroduced populations, but it could be shown that due to following supplementation of populations, genetic diversity and also effective population size in the wild stabilized or even increased. Multivariate (DAPC) and Bayesian inference (STRUCTURE) revealed admixture of supplemented individuals with wild-born individuals. Although population size estimates differed strongly between populations, a link between census size, breeding lines, effective population size and genetic diversity could not be proven. This study highlights that genetic monitoring is not only descriptive but also reveals detailed information on reintroduction success, admixture and population development. We recommend that genetic monitoring should be a basic element of reintroductions and should be used to optimize reintroduction attempts.