Genetic variation in seven relict populations of Saxifraga cernua from three regions of the Alps was investigated using RAPD (random amplified polymorphic DNA) markers. No variation, either within the populations or within the regions, could be demonstrated. Nevertheless, each alpine region was characterized by a unique RAPD phenotype. Absence of genetic variation in these relict populations is attributed to population bottlenecks and founder effects during or following the ice ages. Contrasting hypotheses about the history of these populations, either as survivors of the glacial period or as products of postglacial immigration, are discussed in the light of the data presented.
Draba ladina (Brassicaceae) is a small alpine flower endemic to the Swiss Alps. It occurs exclusively at elevations between 2600 and 3000 m and is restricted to less than a dozen mountains in the Lower Engadin. Morphological characters and polyploidy suggest a hybrid origin. Potential diploid progenitor species are distributed widely and often occur sympatrically. To study the evolutionary history of D. ladina we assessed intra- and interspecific sequence variation at noncoding chloroplast DNA loci and nuclear rDNA ITS sequences in D. ladina and its presumed progenitor species D. aizoides, D. dubia, and D. tomentosa. A single ITS (Internal Transcribed Spacer) genotype was found in each of D. aizoides and D. dubia and two in D. tomentosa. Additivity of ITS sequences of D. aizoides and D. tomentosa was found in D. ladina, supporting the hypothesis of an allotetraploid origin. Intraspecific cpDNA variation was found in all diploid species, but not in D. ladina. The single chloroplast DNA haplotype found in the latter was closest to one cpDNA haplotype found in D. tomentosa, suggesting that D. tomentosa was the maternal parent. These results suggest that D. ladina is a relatively young, presumably postglacial, taxon with a single allopolyploid origin.
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