From East Asia to Beringia: reconstructed range dynamics of Geranium erianthum (Geraniaceae) during the last glacial period in the northern Pacific region

Geranium erianthum is an alpine plant growing in dry habitats, which is distributed from East Asia to northern coastal regions of the northern Pacific. The ice-free area around the current Bering Strait (i.e., Beringia) had played an important role in range expansion into neighboring regions such as East Asia and North America for some alpine plants. However, recent studies suggest that some alpine plants in snowbed environment spread from East Asia to northern coastal regions of the northern Pacific. In this study, we investigated phylogenetic relationships and genetic differentiations among populations of G. erianthum and the related species using the chloroplast genome and single-nucleotide polymorphisms, to evaluate the alternative biogeographic hypotheses in which region of Beringia, British Columbia or East Asia is probable for its distributional origin. Range reconstruction based on phylogenetic tree of chloroplast genome indicated G. erianthum and related species originated in East Asia, from where G. erianthum migrated eastward into Beringia and British Columbia. In addition, nuclear genome-wide SNPs indicated that no significant genetic differentiation was detected between Japanese and Beringian populations. The lack of genetic differentiation suggests that the current range of G. erianthum resulted from rapid range expansion during the latter period of the last glacial era. Overall, the East Asian refugium hypothesis was applicable to the alpine plant G. erianthum in dry habitat, indicating that range expansion pattern from East Asia into the northern Pacific may be more common rather than limited for snowbed species.