Genetic variation within the arctic-alpine Calamagrostis stricta (Poaceae) species complex in Europe

Abstract The Calamagrostis stricta (Poaceae) species complex is a circumpolar, boreo-arctic and montane taxon that includes numerous subspecies and varieties. The recent discovery of Calamagrostis lonana in the Alps calls for a thorough assessment of relationships within C. stricta . The main aim of our study was to elucidate the phylogenetic position, genetic structure and ploidy level of C. lonana , as compared to the other members of the C. stricta species complex from Central Europe to the Arctic. Fifteen populations of the C. stricta species complex were sampled across Central and Northern Europe, and their ploidy level was estimated using flow cytometry. Genetic variation was characterized using double digest RAD sequencing reads (ddRAD-seq) on a total of 115 individuals genotyped at 1157 single-nucleotide polymorphisms. Based on flow cytometric measurements, tetraploidy was observed in Arctic populations from Northern Europe and C. lonana in the Alps, in contrast to other populations exhibiting higher ploidy levels. Calamagrostis lonana was genetically closely related to the arctic C. stricta subsp. groenlandica , while C. stricta subsp. stricta formed a second genetic cluster across Central Europe. A third, very distinct genetic cluster was observed in the northern Svalbard archipelago. Despite lacking evidence of sexual reproduction, substantially more genetic diversity than expected under asexual reproduction was detected within populations in C. lonana and other taxa. The distribution and genetic structure of the C. stricta species complex has been shaped by major post-glacial environmental changes having affected cold regions and specifically highlights C. lonana as a valuable relict taxon for the Alps .