Relict populations and central European glacial refugia: the case of Rhododendron ferrugineum(Ericaceae).
Aim: To assess the origin and genetic relationship of the northernmost population of Rhododendron ferrugineum in the Karkonosze Mts. (the Sudetes), located 350 km north of the previously acknowledged species limit, in the context of the whole species range; to discuss, based on this case study, the glacial history of the Central European mountain flora and importance of rare, relict populations for biogeographical inference and diversity conservation. Location: European mountains: Sudetes, Alps, Pyrenees. Methods: We sampled 90 individuals from 26 R. ferrugineum populations spanning the whole species' range. To infer genetic structure, diversity and relationships among populations and isolated parts of the geographical range, we applied genome-wide amplified fragment length polymorphism (AFLP) genotyping and sequencing of four cpDNA fragments and nrDNA ITS region. Results: Our AFLP analysis revealed four distinct genetic groups in R. ferrugineum, one formed by the northernmost population from (a) the Karkonosze Mts. (the Sudetes) and the other three comprising populations from the (b) Western Alps and Pyrenees, (c) South-Westernmost Alps and (d) Eastern Alps. Genetic isolation of the Karkonosze population was further corroborated by a repetitive pattern differentiation in plastid DNA sequences, otherwise almost monomorphic across the range. Population from the Karkonosze was most closely related to those from the Western Alps and not from the geographically closest Eastern Alps. Main conclusions: We show that the population of R. ferrugineum in the Karkonosze Mts. is a glacial relict and not a recently established or introduced population. Its distinctiveness and high genetic diversity show that it represents a northern, previously undetected, genetic lineage of the species in Europe, which persisted through climatic changes in a small but stable microrefugium. Our case study highlights the importance of an adequate coverage of a species' range in phylogeographical studies and the significance of peripheral parts of the range to reveal biogeographical history of lineages. It also supports the Karkonosze Mountains as an important refugium for the Central European mountain flora.