Enhanced sampling refines the biogeography of the freshwater green alga Aegagropila linnaei (Cladophoraceae)

ABSTRACT A phylogeographic approach is the only way to study the dispersal history of most algae, which are rarely preserved as fossils. However, the only freshwater alga for which this approach has been applied on a Eurasian scale is the endangered green alga Aegagropila linnaei, which is thought to be a poor disperser. Previous phylogeographic results were explained by stepwise dispersal across the Holarctic from an ancestral area in Japan, with further survival in European ice-dammed glacial lakes and extinction in continental Siberia, which lacks such refugia. To clarify the biogeography of A. linnaei in Eurasia we supplemented the published data on its ribotype (internal transcribed spacer of ribosomal DNA) distribution with data from previously unexplored East Europe, Mongolia and the Russian Far East. We have found two new ribotypes, one scattered across temperate Europe and another confined to one locality in the north-eastern Russian Far East. We also expanded the distribution of a ribotype previously reported from Scotland and continental West Europe to include East Europe, Iceland and Central Mongolia. Phylogeogeographic approach based on enhanced sampling allowed us to refine the biogeography of A. linnaei. We discuss reasons for underestimation of A. linnaei dispersal potential. A focused inventory of A. linnaei will likely reveal new localities of the species enabling a further improvement in biogeographical reconstructions. Area-wide studies of other freshwater algae in Eurasia need to be performed to test the generality of the revealed biogeographical patterns.