Quaternary range shifts, hybridization and ecological niche evolution in Saxifraga sect. Saxifraga subsect. Arachnoideae
Final Report Abstract
The 12 species of Saxifraga sect. Saxifraga subsect. Arachnoideae, distributed largely in the European Alps, are most remarkable in terms of ecological diversification by containing both species from exposed high elevation (up to 4200 m) and species from shady low elevation habitats. An enigmatic example for the latter group is Saxifraga berica limited to a small area in the Colli Berici near Vicenza (northern Italy) outside the Alps where it grows in shady hollows under overhanging rocks at elevations lower than 450 m. The existence of a third group of species with various combinations of these extreme habitat properties in combination with incongruency between nuclear- and plastid-based phylogenetic trees found in previous analyses of subsect. Arachnoideae had led to the hypothesis that interspecific hybridization might have affected the evolution of ecological traits in this lineage. Using a hybrid capture based target enrichment approach and 41 ingroup samples of all 12 species we reconstructed and dated a phylogenetic species tree, identified instances of interspecicific hybridization and used the tree for the reconstruction of the evolution of ecological trait. Much in contrast to our original expectation, interspecific hybridization in the study group did not affect the evolution of ecological preferences. Instead, on the background of a) phylogenetic relationships found, b) the evolution of ecological preferences in subsect. Arachnoideae and c) the distribution of species with divergent ecologies particularly with respect to light and soil pH requirements in well-known glacial refugia, we hypothesized that the extant ecologies of S. berica, S. paradoxa and S. arachnoidea, exceptional in terms of soil pH and/or light requirements, originated through adaptive evolution in glacial refugial areas where these species persisted upon climatic warming in interglacials. We believe that our study contributes to a better understanding of plant evolution in response to the climatic oscillations of the Quaternary. In particular, we highlight the possible role of Quaternary interglacials. As interglacials of the Quaternary were considerably shorter than glacials, the possibility of interglacial evolution is remarkable considering that it has been questioned that even glacials were long enough for evolutionary divergence.
Publications
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Species composition of Saxifraga sect. Saxifraga subsect. Arachnoideae (Saxifragaceae) based on DNA sequence evidence. Willdenowia, 50(2), 225.
Gerschwitz-Eidt, Michael A. & Kadereit, Joachim W.
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Adaptive evolutionary divergence of populations persisting in warming cold-stage refugia: candidate examples from the periphery of the European Alps. Alpine Botany, 133(1), 1-10.
Kadereit, Joachim W.
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Phylogeny of Saxifraga section Saxifraga subsection Arachnoideae (Saxifragaceae) and the origin of low elevation shade‐dwelling species. Ecology and Evolution, 13(1).
Gerschwitz‐Eidt, Michael A.; Dillenberger, Markus S. & Kadereit, Joachim W.
