Long-distance dispersal vs vicariance: the origin and genetic diversity of alpine plants in the Spanish Sierra Nevada.

Here, we investigated the origin and genetic diversity of four alpine plant species co-occurring in the Spanish Sierra Nevada and other high mountains in south-western Europe by analysis of amplified fragment length polymorphisms (AFLPs). In Kernera saxatilis, Silene rupestris and Gentiana alpina we found intraspecific phylogroups corresponding to mountain regions as predicted by the vicariance hypothesis. Moreover, genetic distances between Sierra Nevada and Pyrenees populations were always higher than those between populations from the Pyrenees and the south-western Alps/Massif Central. This suggests successive disruption of gene exchange between mountain ranges as postglacial climatic warming proceeded from south to north. In Papaver alpinum, our data indicate that a central Pyrenean population arose via long-distance dispersal from the Sierra Nevada, and that vicariant separation events between the Sierra Nevada and the Pyrenees and between the Pyrenees and the south-western Alps occurred simultaneously. Overall, Sierra Nevada populations of all species investigated here preserve unexpectedly high (or not exceptionally reduced) genetic diversity. This testifies to the important influence of long-term isolation, i.e. vicariance, on genetic diversity through fostering the accumulation of new mutations and/or the fixation of ancestral ones.