Phylogeography and genetic structure of a subarctic-alpine shrub species, Alnus alnobetula (Ehrh.) K. Koch s. l., inferred from chloroplast DNA markers

The green alder Alnus alnobetula s. l., a widely distributed subarctic-alpine shrub species, has been studied using three chloroplast DNA regions: trnH-psbA, trnS-trnG, and psaA-trnS. In addition, new chloroplast primers coding the trnT-GGT cpDNA regions and five cpDNA microsatellite loci (cpSSR) have been developed for this species. The population subdivision is very high (Nst = 0.869, Gst = 0.807, Fst = 0.883), suggesting a distinct phylogeographic structure (Nst > Gst, p < 0.0001) and a sharp contrast between the haplotype-rich eastern part of the species range and the almost completely uniform western part (Siberia, Ural). According to a phylogenetic analysis, the common haplotype of A. alnobetula subsp. fruticosa in the western part of the range originated from northeastern refugia (West Beringia) as a result of interglacial recolonization, including bottleneck events. Three highly divergent cpDNA lineages of green alder that have been resolved in the Russian Far East are largely concordant with A. alnobetula subsp. kamtschaticа, A. alnobetula subsp. mandschurica, and A. alnobetula subsp. maximowiczii. The populations of Sakhalin Island are divided into three phylogeographic groups (southern, central, and northern) corresponding to the different floristic zones and different subspecies. The green alder populations from central Sakhalin have a haplotype-rich composition including different genetic lineages that confirm the existence of a hotspot of genetic diversity in this part of the island.