Impacts of forest fragmentation and post-glacial colonization on the distribution of genetic diversity in the Polish population of the hazel grouse Terastes bonasia

Abstract

While the hazel grouse Tetrastes bonasia declined in the twentieth century to the point where certain local subpopulations in Poland disappeared altogether, the overall population of the species in the country now seems to be back on the increase. To consider the remaining genetic diversity in that population, analyses of a fragment of the hypervariable domain I of the mitochondrial control region were performed on faecal samples from 251 of the birds. This work provided confirmation of conclusions drawn from previous observations that birds in the populations present in smaller and more isolated forests were characterised by more limited genetic diversity than those occurring in continuous, less-fragmented forests. The level of genetic diversity among birds from central Poland is also found to be high, most likely because recent recolonisation there has involved individuals from both the north and south of the country, as is also suggested when migration rates are estimated. Analysis further indicated a pronounced genetic structure, with a range of processes seen to affect genetic differentiation from one region of Poland to another. Analysis of molecular variance (AMOVA) provided for an assignment of populations to groups corresponding well with the geographical distribution of forests in Poland. Gene flow among the populations is shown to be very low, with no more than 1.5 female migrants per generation coming in. Both high nucleotide diversity and mismatch distribution, and the AMOVA and nested clade analysis (NCA) suggest that birds following at least two different post-glacial recolonisation routes encountered one another in north-eastern Poland. Equally, there are clear indications that the north-eastern and southern parts of the country were recolonised in different periods. The genetic results presented here underline the importance of gene flow in maintaining genetic variability within populations of the hazel grouse, at the same time suggesting that the country’s southern and north-eastern populations should be managed independently where conservation efforts are concerned.