A circumpolar study of Arctic biodiversity:: Phylogeographic patterns in the Daphnia pulex complex

We summarize the results of a circumarctic study on biogeographic patterns in genetic diversity within asexual clones of the water flea, the Daphnia pulex complex (a freshwater crustacean). The complex is shown to consist of several thousands of distinct clones, which can be grouped into 2 major lineage groups based on molecular markers. The main groups and their component subgroups differ markedly in their distributions, and hybrids are common in 2 zones of overlap (Northern Europe and Canada). Clonal diversity is at least as high in the Arctic as in the temperate zone. Moreover, the genetic structure of all the subgroups is extremely fragmented, implying that clonal composition in the Arctic differs conspicuously among regions. This extraordinary diversity with its spatial structure on local to continental geographic scales defies the general notion of the Arctic tundra as a homogenous biome of low biodiversity.