Genetic diversity patterns of the orchid Anacamptis pyramidalis at the edges of its distribution range

Populations at the margins of a species’ distribution range are often smaller and more spatially isolated compared to centrally located populations. Therefore, a decline in within-population genetic variation and increased differentiation among populations towards range edges is expected. The edge effect can be enhanced by historical range expansions following glaciations in populations located at high latitudes. We investigated the level and distribution of genetic variation between 17 populations (collected from six countries) of the terrestrial orchid Anacamptis pyramidalis, using AFLP markers. Our study revealed no decline in genetic diversity in disjunct populations in Estonia at the northern border of the distribution area of this species, nor in the populations located at the southern edge of the range, on the island of Cyprus. Similarly, edge populations were not more differentiated from each other than the central populations in Slovenia and in Spain. Our results suggest that the degree of genetic variation is determined by the size of populations rather than geographic location of this species and underlines the impact of long-distance gene flow on the maintenance of genetic diversity in connection with major range shifts in the past.