Population genetics in a fragmented population of the European tree frog (Hyla arborea)

Abstract

Habitat degradation and fragmentation are known to be major threats for population persistence in European amphibians. The European tree frog Hyla arborea has suffered from dramatic population declines in the last decades and has therefore been categorised as threatened in many Red Data lists. In the region of Hannover (Germany), the European tree frog has a fragmented distribution. The aim of our study was to infer the genetic consequences of habitat fragmentation in this area by examining genetic variation and population structure. DNA samples from 193 individuals from 11 sampling sites (10 sampling sites located 2 to 32 km apart from each other near Hannover and for comparison one sampling site 140 km northeast) were analysed with eight highly polymorphic microsatellite loci. Bayesian analyses indicated that the tree frog occurrences near Hannover were fragmented into four genetically distinct clusters according to their geographical distribution. Pairwise genetic distances between sampling sites varied between 0 and 0.23 (FST) and 0 and 0.48 (Dest) and indicated high to moderate gene flow within genetic clusters and nearly absent gene flow among genetic clusters. Moreover, we identified a potential source population within the region for an introduced population in the southwest of Hannover. Our data suggest that the genetic structure is influenced in part by isolation by distance and in part by lack of habitat or migration barriers. Habitat fragmentation should by counteracted by targeted conservation measures in areas where gaps in distribution and genetic fragmentation have been revealed.