The project includes RAD-tags from 306 individuals of Carex scirpoidea (Cyperaceae) collected throughout its distribution range.. Population genomics Carex scirpoidea

Quaternary glaciations have played a major role in shaping the genetic diversity and distribution of plant species. Strong paleoecological and genetic evidence supports a postglacial recolonization of most plant species to northern Europe from southern, eastern, and even western glacial refugia. Although highly controversial, the existence of small in situ glacial refugia has recently gained molecular support. We use genomic analyses to examine the phylogeography of a species that is critical in this debate. Carex scirpoidea Michx ssp. scirpoidea is a dioecious, amphi-Atlantic arctic-alpine sedge that is widely distributed in North America, but absent from most of Eurasia, apart from three extremely disjunct populations in Norway, all well within the limits of the Weichselian ice sheet. Range-wide population sampling and variation at 5307 SNPs show that the three Norwegian populations comprise unique evolutionary lineages with low genetic diversity within and high divergence between populations. At a higher hierarchical level, two distinctly divergent evolutionary groups were observed: one eastern group containing populations from Greenland and Norway, and prevailing in populations from Minnesota and Michigan, and a second western group containing populations from Alaska and Yukon, while prevailing in populations from British Columbia and Colorado. Demographic analyses support one single, pre-Weichselian colonization into Norway from East-Greenland, and subsequent divergence of the three populations in separate refugia. Other refugial areas are identified in Northeast-Greenland, Minnesota/Michigan, Colorado and Alaska. Admixed populations in British Columbia and West-Greenland indicate postglacial contact. Taken together, evidence from this study strongly indicate in situ glacial survival in Scandinavia.