Genetic monitoring to assess the success of restoring rare plant populations with mixed gene pools

Increasing genetic diversity and maintaining evolutionary processes are primary goals of conservation translocations, which involve the intentional movement of an at-risk species to establish new populations or augment existing populations, with the ultimate goal of reversing declines. Much debate has focused on how to select source material for plant translocations, with early approaches focusing primarily on maintaining the genetic uniqueness of populations. However, recent strategies often advocate mixing population sources during translocation to increase genetic diversity and re-establish connectivity. Yet, despite hundreds of translocations programmes with at-risk plant species presently underway (e.g. Silcock et al., 2019), few studies have conducted thorough assessments of the effects of mixing population sources on both the genetic diversity and fitness of translocated populations. The study by Van Rossum et al. (2020) in this issue of Molecular Ecology uses detailed assessments of genetic parameters and fitness to understand the outcomes of mixing two genetically differentiated source populations in translocations of the rare, self-incompatible perennial herb, Arnica montana, whose populations are declining at low elevations in Western Europe. They examine genetic changes throughout the translocation process (source populations to F1 offspring) and demonstrate the maintenance of high genetic diversity in successive generations for all three translocations. Translocated populations exhibited high contemporary pollen flow, substantial admixture between source populations and low inbreeding in F1 offspring. Importantly, they found no evidence of outbreeding depression in F1 offspring. This work shows that genetically mixing source populations can result in optimal genetic outcomes in translocations of declining plant species and exemplifies how multigenerational genetic monitoring and fitness assessments can be used to evaluate the success of experimental translocations.