Immigration of the thermophilous, bird-dispersed Empetrum nigrum s. lat. to Svalbard

The arctic archipelago of Svalbard was almost completely ice-covered during the last glaciation. If any, only very hardy species could have survived the glaciation in situ. Empetrum nigrum is one of the most thermophilous plants occurring on Svalbard today, and must have arrived postglacially by long-distance dispersal. In this study, AFLP fingerprinting and ploidal level determinations using flow cytometry were used to determine the source area(s) of the Svalbard populations of E. nigrum. A total of 435 individuals from 46 populations in the northern hemisphere, mostly from the North Atlantic area, were analysed. PCO- and Bayesian clustering analyses separated the tetraploid E. nigrum in the North Atlantic area into a northern and a southern group. Svalbard belonged to the northern group. These two main groups of tetraploid E. nigrum probably reflect survival in different glacial refugia during the last and/or previous glaciations. A main refugium east of the Scandinavian ice sheet is suggested for the northern group, while a main refugium south of the Scandinavian ice sheet is suggested for the southern group. Allocation analyses strongly suggest that E. nigrum colonised Svalbard from East Greenland, which again was colonised from West Siberian/Ural Mountains source populations. The western North American and the East Siberian plants were separated into a third group that appeared to be most closely related to the northern Atlantic group. However, the present study comprises too few populations in the Beringian area to draw firm conclusions about this third group. Two suture zones with high levels of genetic diversity were identified; the Ural Mountains and South West Greenland. The southern and northern group met in the Ural Mountains, while South West Greenland is probably influenced by both the southern and the northern group, and one or several Beringian lineages