Importance of Beringia for the divergence of two northern Pacific alpine plants, Phyllodoce aleutica and Phyllodoce glanduliflora (Ericaceae)

The Pleistocene glaciations largely influenced species distributions and caused allopatric divergence. Multiple biogeographic processes have contributed to the diversification of the alpine flora around the coastal rim of the north Pacific, which includes survival in Beringian refugia, dispersal between East Asia and North America via the Bering land bridge and range division by continental ice sheets in North America. To assess the history of alpine plants in the northern Pacific Rim, we address the divergence of two alpine shrub species, Phyllodoce aleutica and P. glanduliflora (Ericaceae). Species trees based on sequences of 21 nuclear loci revealed that they are sister species (bootstrap support = 89 and posterior probability = 0.74). Model-based analyses of their speciation history demonstrated that P. aleutica and P. glanduliflora likely diverged without gene flow during the middle/late Middle Pleistocene (c. 307-209 kya). In addition, the inference of ancestral areas on the species tree indicates that their speciation occurred in Alaska, from which P. aleutica spread into East Asia and P. glanduliflora into North America. Accordingly, our study suggests that geographic isolation in separate areas within Beringia played important roles for diversification of alpine plants in the northern Pacific Rim.