Effects of Isolation and population size on genetic variability in European black grouse (Tetrao tetrix)

We studied microsatellite genetic variation in different geographic populations of black grouse (Tetrao tetrix) across the European range. We applied a clustering algorithm based finding genetic clusters in linkage and Hardy-Weinberg and identified 5 independent clusters. These clusters were consisting of: Fenno-Scandian; British, Alpine, Dutch and lowland populations from Austria and Germany, respectively. Based on previous knowledge, populations were grouped in to three different categories: isolated, contiguous and continuous, respectively. Genetic diversity, measured as observed (HO) and expected heterozygosity (HE), respectively, were lower in isolated populations as compared to the other two categories that did not differ amongst one another. We found a higher number of alleles in contiguous populations as compared to isolated ones and yet more in continuous populations. Observed heterozygosity and average number of alleles showed positive relationships with estimates of census population size. These results imply that lowered genetic variability in black grouse populations is affected by both population size and isolation but the independent effects of each of these are hard to disentangle. Bottleneck analyses suggested that British populations and one isolated population in central Germany (Rhön) have been recently bottlenecked. It is possible that isolated populations may recover in numbers from population bottlenecks. However, to restore genetic variability requires longer time and connectivity. Our results imply that the connectivity of small and isolated populations in Western Europe should be improved or else these face the risk of extinction due to genetic and demographic stochasticity