Chloroplast DNA variation of white oaks in the alpine region

Abstract

After the last glacial maximum the Alps have represented a major obstacle to the recolonisation of central and northern Europe by flora and fauna surviving in southern refugia. It is also believed that the Alps may have acted as a temporary refugia for some species, harbouring significant genetic variation or allowing the evolution of new genotypes and subspecies. To examine this possibility for white oak species, a total of 1375 samples from 292 locations were sampled in alpine and flanking regions of Austria, France, Germany, Italy and Switzerland and were assessed for cpDNA variation. Of the oak samples taken, throughout the entire alpine area Quercus robur was found most frequently. Quercus pubescens, widespread in Switzerland, Italy and up to the northern part of the French Alps was found south of 47°N and thus absent from Germany and sparse in Austria. Quercus petraea was mainly found in the parts of the Alps west of 12°E. Absent in the high elevations of the Austrian Alps Q. petraea and subspecies can be found at the eastern flank of the Alps. A total of 11 different haplotypes were found within the alpine area. Most frequent are different members of lineage A (common in the Balkan refugial area) with haplotype 7 found in 64% of the sample set. Haplotype 5, a more eastern member of the lineage, was found at the eastern flank of the Alps. Approximately 22% of the samples belonged to lineage C (from the Italian refuge), almost all of them were haplotype 1 with the majority crossing the Alps in Switzerland at the Simplon pass. Haplotype 2, the more eastern member of lineage C originating in Italy, is found at low frequency to the east of the Alps and in the Danube valley. Oak from refugial areas in Spain (lineage B) had only a limited impact on the alpine region. In spite of the historical anthropogenic influence in the alpine region, clear tracks of recolonisation were uncovered. In particular, the path of northward migration of oaks from Italy and the major route north of the Alps were clearly elucidated, confirming earlier assessment of pollen core data. However, the direction of migration (east to west or west to east) of oaks from the Balkan (haplotype 7) around the Alps still needs to be resolved.