Phylogeographical structure of a narrow endemic plant in an isolated high-mountain range

Abstract

Phylogeographical analyses of alpine species in temperate Europe, distributed in island-like habitats in high-mountain ranges, generally focus on widely distributed species at wide geographical scales. However, genetic diversity and population differentiation in the alpine zone is strongly associated not only with patterns in large-scale isolation, but also local topographic structure of habitats. Regionally endemic species offer the possibility of a realistic overview of genetic diversity in relation to local scale history without the effect of unrecognized external gene flow. Here, we focus on Cochlearia tatrae, a narrow endemic species occurring only within an isolated highmountain area in the Tatra Mts. Based on population sampling across its entire range, AFLP genotyping and DNA sequencing (non-coding plastid DNA and nrITS) this species’ genetic structure was assessed in the spatial context of its distribution and discussed in terms of its Late Pleistocene history. Pattern of genetic structure in C. tatrae populations did not include strongly divergent genetic lineages with high levels of unique genetic markers. In the PCoA and Neighbour-Net analyses of AFLP data, individuals formed a genetically coherent complex. However, despite the lack of discontinuities, the general tendency was for them to cluster in a way that reflects individual populations and geographical provenance. Despite the small area of distribution of this species (~80 × 20 km), the Bayesian analysis of population structure revealed four genetic groups, with a latitudinal (east–west) distribution across the Tatra Mts. CpDNA and ITS sequences varied little but localized distribution of several closely related plastid haplotypes mostly supported the delimitation of the genetic groups. Based on this phylogeographical structure it is assumed that the Last Glacial history of C. tatrae was characterized by vertical movements and isolation in peripheral, periglacial microrefugia where the conditions were cold and moist. Subsequent postglacial upslope movements, together with poor dispersal and little gene flow resulted in several genetic lineages distributed longitudinally along the Tatra Mts.