Genetic impoverishment of the last black grouse (Tetrao tetrix) population in the Netherlands

We have studied a small isolated bottlenecked population of Black grouse (Tetrao tetrix) in the Netherlands to examine the impact of isolation and reduction in numbers on the genetic diversity. We compared the genetic diversity in the last present Dutch population with Dutch museum samples and three other Black grouse populations (from England, the Alps and Norway, respectively) representing known isolated and non isolated populations. We also compared with Black grouse from a Dutch breeding program. We found significantly lower allelic richness, observed and expected heterozygosity in the present Dutch population compared to the non isolated populations (the Alps and Norway). Signs of heterozygosity deficiency were only found in the Dutch museum samples and the isolated population in England. Genetic drift was evident in the present Dutch population in comparison to the reference populations, as assessed both in pair wise FST and Structure analyses. The effect of a bottleneck was simulated using census data from 1945 and onwards with the Dutch museum samples as a model for the initial population. Number of alleles and observed heterozygosity was within the standard error range of the present Dutch population under the assumption of a 50:50 sex ratio and random mating. The Dutch museum samples showed signs of genetic impoverishment, possibly due to the ongoing decrease in numbers over the last 50 years and a probable Wahlund effect as a cause of sampling over different populations. The lack of evidence for a bottleneck and heterozygosity deficiency in the present Dutch population is proposed to be accredited to a rapidly found new equilibrium as a consequence of a very small effective population size.