Vicariance and dispersal in the alpine perennial Bupleurum stellatum L. (Apiaceae)

Using Amplified Fragment Length Polymorphism (AFLP), we explored the intraspecific phylogeography of the alpine vascular plant Bupleurum stellatum (Apiaceae), disjunctly distributed in the Alps and Corsica. Within the Alps, the species' distribution area is also not contiguous, spatially isolated groups of populations occuring in the Dolomites (Italy) and the Montafon (Austria). A main goal of our Study was to explore the degree of differentiation of the isolated populations in Corsica, the Dolomites and the Montafon from the populations in the main distributional area and to test for hypotheses of vicariance or dispersal. We also sought a better general knowledge of glacial refugia of low alpine silicicolous plants. Phenetic as well as cladistic analyses of the AFLP multilocus phenotypes reveal a substantial north-south split through the contiguous distribution area of B. stellatum in the Alps. The resulting phylogeographic groups can be related to glacial refugia in peripheral areas of the Alps that were recognised in previous Studies. The disjunct populations in Corsica, the Dolomites and the Montafon, however, are less strongly differentiated. For example, the Corsican population clustered with high bootstrap support with populations from the Eastern Alps, suggesting immigration to Corsica from that region. Our study shows that deep phylogeographic splits resulting from old vicariance events can be concealed by presently contiguous distribution areas. In contrast, disjunctions, if they are due to dispersal events, need not be accompanied by genetic divergence.