Amplified fragment length polymorphism (AFLP) suggests old and recent immigration into the Alps by the arctic-alpine annual Comastoma tenellum (Gentianaceae)

Aim This study aims to elucidate the phylogeography of the arctic-alpine annual Comastoma tenellum (Rottb.) Toyok. (Gentianaceae) and to unravel the history of its immigration into the Alps. Location Although samples from Alaska and Central Asia were also included, our study focusses on Europe, especially on the Alps. Methods We applied amplified fragment length polymorphism (AFLP) fingerprinting on 37 populations (162 individuals) of C. tenellum and analysed the results phenetically. Results As C. tenellum is mainly inbreeding, there is typically little to no intrapopulational genetic variation. Two populations from Alaska and Altai are strongly separated from all other accessions. The majority of the populations from the Alps group together with high bootstrap support. They fall into an unsupported Alps I group (northwards of Gran Paradiso) and a well-supported Alps II group (south-western Alps). The remaining European populations form a weakly-supported branch constituting accessions from the Carpathians, Scandinavia and two populations from the Eastern Alps. Main conclusions Comastoma tenellum reached the Alps at least twice. The first immigration event resulted in a lineage that is clearly separated from the other European accessions. The immigration must have occurred well before the last glaciation because this lineage shows further phylogeographical structuring into two groups (Alps II in the south-western Alps and Alps I in the rest of the Alps). This pattern is presumably due to isolation in different glacial refugia. In addition to the old immigration event, the species reached the Alps in recent times either from Scandinavia or from the Carpathians via long-distance dispersal. These immigrations resulted in (at least) two populations that are spatially small and poor in individuals.