Phylo-Geographie von Arabis alpina L. (Brassicaceae)
Kirchner, Dorothea E.
published: Dec 19, 2002
The objective of this study was to use molecular methods to test different hypotheses about the glacial and post-glacial distribution and immigration of Arabis alpina in northern Europe. In total ninety-two populations of the species were investigated. These were sampled from various circumpolar regions, including Canada, Greenland, Iceland, Scandinavia and Russia, but also from regions farther to the south, including the German uplands, the Alps, the Pyrenees, the Swiss Jurassic, the Italian Apennines, the islands of Sicily and Rhodes, the Karpaten and Sudeten of Poland, Turkey, the mountains of Ostsaljan in Russia, the Zagros mountains in Iran, the Asir mountains in Saudi-Arabia and the mountains of East Africa. Sequence analyses of the species' nrDNA (ITS1 and ITS2) and cpDNA (trnT/trnL-spacer, trnL-intron, trnL/trnF-spacer) did not show any variability. The intraspecific phylogeny of A. alpina could not be resolved by this marker, and the sequencing of nrDNA and cpDNA did not prove to be a useful molecular marker for the biogeographical questions asked here. In general, RAPD-analyses resulted in a high genetic diversity, which corresponds to the high morphological variability of A. alpina. The low genetic diversity of circumpolar populations of the species supports the Tabula-rasa-Theory. High DNA-variability of the populations in the North of Spain (Pyrenees), Italy (Apennines) and the Balkan region gave evidence to the hypothesis that these areas represented refuges for A. alpina during the glacial period. The genetic diversity continuously decreases from the refuges towards northern regions. This backs up the hypothesis that the interglacial and post-glacial immigration of A. alpina proceeded from the refuges towards the north. It has been assumed that the populations of A. alpina in East Africa were isolated from European and North American populations at least since the last glacial period (about 11.500 years ago). This was supported by the RAPD-data. The trees of the Neighbor-Joining analysis, the cluster analysis and the parsimony analysis proved a base position of the populations in East Africa, Iran and Saudi-Arabia in contrast to all other countries. This separation is backed up by high bootstrap- and distance-values. A. alpina originated from West Asia and started to disperse from the Balkan region in two main directions. The first direction led to East Africa via Iran and Saudi-Arabia. The other one led towards the Alps, Italy (Apennines), and the Pyrenees. From these three regions A. alpina moved north to Norway from where it probably spread to Iceland, Greenland and possibly to Canada.