Conservation genetics of a mirrored population of the European tree frog (Hyla arborea)

Population decline and local extinction of amphibian populations have increased in the last decades. The European tree frog (Hyla arborea) is particularly endangered in its northern distribution range. One of the suggested conservation strategies for threatened amphibians is resettlement. The Okologische Schutzstation Steinhuder Meer e.V. (OSSM) started a resettlement project in 2008 for the European tree frog in Lower Saxony and North Rhine-Westphalia, Germany. Hereby, individuals were translocated from a donor population to a location approximately 40 km distant, establishing a mirrored population. The objective of this study was to monitor genetic diversity of these two populations and genetic exchange with a nearby located population at Lake Steinhuder Meer. Therefore, a total of 91 individuals were analysed at 12 species-specific nuclear markers (microsatellite loci). The genetic diversities of the three populations were almost similar but the mirrored population (H-e = 0.66) exhibited a small reduction compared to its donor population (H-e = 0.72). Significant indications for a recent bottleneck were detected for the donor and mirrored population. However, the mirrored population seems to have recovered from founder effects, since the actual number of calling males surveyed at this site since establishment reveals a stable and steadily growing population. F-ST values and D-est values showed significant differentiation between all sites with a global F-ST of 0.08. Likewise, results of a Bayesian clustering analysis indicated the existence of three genetic clusters. The software Geneclass2 assigned nearly half of the individuals of the mirrored population to its source population. Furthermore, the analysis suggested recent migration between the mirrored population and Lake Steinhuder Meer. Compared to other Hyla populations the genetic diversity was high at all localities and population sizes seem to have increased. We conclude from our study that resettlement projects can be efficient measures to counteract amphibian population decline when supported by population genetic analyses.