Where did the northern peatland species survive the dry glacials:: cloudberry (Rubus chamaemorus) as an example

Aim During the last ice age large parts of the north boreal and subarctic zones were covered by ice, while the climate in ice-free regions of northern Asia was extremely cold and dry. The extensive peatlands of these zones with their characteristic vegetation developed at the beginning of the Holocene. We combine a phylogeographical approach with maps of pollen records to identify regions where Rubus chamaemorus, a plant of moist, peaty soils, was likely to grow during this period. Location Circumarctic/circumboreal. Methods Samples were collected from 45 locations throughout much of the range of R. chamaemorus and 398 plants were analysed with amplified fragment length polymorphism (AFLP). Estimates of diversity and differentiation, principal coordinates analysis and Bayesian clustering methods were used for the analysis of genetic data. Dated pollen records were retrieved from the European and the Global Pollen Databases. Results The plants from Sakhalin are highly divergent from the rest of the material and represent the previously described var. pseudochamaemorus. The main genetic division in R. chamaemorus sensu stricto is found in the Taymyr region in central Eurasia. Genetic diversity and the relative number of rare markers are highest in central Siberia and eastern Asia and decrease towards Europe and to a lesser extent eastwards through North America. Pollen dating back to the last ice age is found in central and eastern Siberia and Alaska. The maximum observed clone size is about 250 m, and more than one clone is found in nearly every local population. Main conclusions The genetic data are consistent with the pollen records and indicate that R. chamaemorus was growing in several areas of northern central Siberia and Beringia during the last glaciation. This finding suggests that sufficient humidity for this and other species of peaty soils was present locally in different parts of the generally dry ice-free areas of northern Asia, as had been previously documented for Beringia. The AFLP data show that var. pseudochamaemorus, which is also morphologically quite divergent, clearly represents a distinct genetic entity.