Evolution in high mountain systems (Phyteuma, Campanulaceae)

Alpine habitats (i.e., habitats above the tree-line) are biodiversity hotspots, which is the result of their complex origin and histories. As alpine habitats are considered to be among the most strongly affected by global climate change, alpine species not only are suitable systems for studying processes and mechanisms of speciation in general, but a better understanding of the evolution of alpine species is also relevant for assessing how they may respond to global climate change. An excellent system to study the evolution of species in and into alpine habitats is the plant genus Phyteuma (Campanulaceae). The proposed project will establish a sound species phylogeny for Phyteuma using thorough analyses of two complementary phylogenomic data sets (gene capture and RAD-seq derived SNP data). Based on the thus obtained phylogenetic hypothesis, the prevalent mode of speciation in(to) alpine habitats and putative ecological and morphological (pre-)adaptations will be identified. Specific questions include: Are alpine species the result of repeated speciation into alpine habitats or of in situ speciation in alpine habitats? What are the ancestral habitats of alpine species? What is the role of ecogeographic differentiation for alpine speciation? Are there morphological traits associated with the occurrence in alpine habitats? What is the impact of Pleistocene climatic oscillations on speciation in and/or into alpine habitats? Finally, using target capture and RAD-seq data and ecological modeling approaches, the phylogeographic histories of two widely distributed species complexes will be inferred to address whether a given species colonized alpine habitats once or multiple times, to identify the prevailing directionality of habitat shifts, and to assess the impact of Pleistocene climatic oscillations on differentiation. Phyteuma offers an excellent system to study evolution in(to) alpine habitats at the phylogenetic (species) and the phylogeographic level. As the incorporation of genetic data is expected to lead to more robust predictions of the response of biota to environmental change, the proposed research will contribute to our understanding of possible responses of mountain biota to global change. Sequence data obtained from target capture of specific genomic regions and SNP data from restriction-site associated sequencing (RADseq) are among the main sources of phylogenomic data. Empirical comparisons of their utility at different levels of divergence are still limited, and comparable data from plants are essentially lacking. Providing comparisons of the two main types of phylogenomic data at both the phylogenetic and phylogeographic level within the same organismic group, thereby reducing the potential impact of lineage- specific features, is expected to of broader interest for the (plant) evolutionary community.

The combination of large amounts of molecular data, generated from next-generation sequencing platforms, and of sophisticated modelling tools allows long-standing hypotheses in plant evolution and biogeography to be tested with unprecedented power. An excellent model system for these is the plant genus Phyteuma (rampion) from the bluebell family, where the following questions were addressed: What is the origin of range-restricted, but ecologically barely diverged species? The French endemic Ph. gallicum is found to be of recent (late Pleistocene) origin, which, in contrast to previous hypotheses, did not involve hybridization, but allopatric divergence enforced by Pleistocene range shifts. Hence, the restricted range most likely is a result of the time of origin rather than of ecological constraints, and hybridization with the closely related Ph. spicatum is due to secondary contact. Are there Pleistocene forest refugia north of the Alps? Being a long-standing and contentious issue in biogeography, spatially explicit modelling in Ph. spicatum, a characteristic species of beech forests, provides moderate support for the presence of a northern refugium (in addition to southern refugia), most likely in the Western Carpathians. What is the origin of alpine ecotypes in elevationally widespread species? Elevational differentiation may be an important driver of diversification. Testing this hypothesis in the both geographically and elevationally widespread species Ph. orbiculare shows that the main divergence in this species is longitudinal (i.e., along a gradient from more oceanic to more subcontinental climate) and that higher elevations have been reached in each lineage multiple times independently. It remains to be tested whether such an intraspecific pattern of multiple origins of alpine ecotypes is also true at the interspecific level, but the respective analyses are, at the time of writing, still under way.