A polar projection showing the general regions of contact between diverged DNA clades of six Holarctic species (see text and references for details and Latin binomials). Note the clustering near features like mountain ranges and major rivers. The Scandinavian cluster, which includes a number of other species, forms where the last remnants of the ice cap melted. Last glacial ice caps and sheets are in white, and tundra is darker grey (I am grateful to Richard Abbott for the basic map).
Hewitt Frontiers in Zoology 2004 1:4 doi:10.1186/1742-9994-1-4