Genetic diversity of Dactylorhiza incarnata (Orchidaceae) in northern Poland

The genetic structure of Dactylorhiza incarnata var. incarnata populations is shaped not only by historical events such as recolonization after ice sheet retreat or limited seed and pollen dispersal, but also the bottleneck effect. During the last decade, D. incarnata var. incarnata has also experienced a strong decline in population numbers and sizes, due to habitat loss and fragmentation. In the present research genetic diversity was examined in eight populations located in northern Poland, using six nuclear microsatellites loci. At the species level our results showed a moderate mean level of genetic diversity ( A = 4.67; A e = 2.73; R s = 4.48; H o = 0.438; F IS = 0.224), which varied among the studied populations ( A : 2.17–3.67; A e : 1.55–2.69; R s : 1.31–1.61; H o : 0.292–0.631; F IS : −0.283–0.340). A considerable overabundance of homozygotes was detected in four populations ( F IS within the range of 0.067–0.340), and in the remaining populations an excess of heterozygotes was observed. The average apparent out-crossing rate was also calculated ( t a = 0.980), and primarily indicated a tendency to out-cross within the species. Moderate genetic differentiation was found among the studied populations ( F ST = 0.149; R ST = 0.174; p u003c 0.05). The differentiation of the populations corresponded to relatively low gene flow value ( N m = 0.426) among populations, which amounted to only one migrant every second generation.