Evolution of the European alpine flora

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Hybridization and hybrid speciation are frequent in flowering plants. Reproductive isolation of hybrids from their parental species is of central importance for both homoploid and polyploid hybrid speciation, and it has been suggested that reproductive isolation most commonly is conferred by ecological differentiation between hybrids and parents. Our phylogenetic analysis of Sempervivum provided evidence that populations of the genus from the Rhine Gorge area (Mittelrhein-, Nahe-, Mosel-, Ahrtal) and the Massif Central (France) - both currently classified as S. tectorum - represent homoploid and polyploid hybrid lineages, respectively, between the widespread and edaphically variable (calcicole/calcifuge) S. tectorum and the southwest Alpine and strictly calcicole S. calcareum. We also have evidence for the existence of a hybrid zone between the two parental species in the W Alps. Potentially, this is the first detection of homoploid and polyploid hybrid speciation from the same pair of parental species and would represent an ideal system for a comparative analysis of the role of ecological differentiation in hybrid speciation. The hypothesis of a hybrid origin of the Rhine Gorge, Massif Central and W Alps populations is based mainly on additivity of a limited number of variable nuclear ribosomal intergenic spacer sequence positions in the hybrid material, and on a limited sample of unknown ploidy level particularly of the widespread S. tectorum. The major aim of the project proposed here is to broaden the sample of both parental species, of both potential hybrid lineages and of the hybrid zone populations, and to use a Genotyping-by-Sequencing approach for the generation of highly variable DNA sequences which is expected to provide conclusive evidence on hybrid origin. The material will also be used for the determination of ploidy level. Soil and climate of sample sites will be characterized, and the niches of all lineages will be modelled.