The origin of Arctic terrestrial and freshwater tardigrades

The tardigrade faunas of six Arctic sites (Canadian Axel Heiberg I., east and west coasts of Greenland, Iceland, Svalbard, Novaya Zemlya and the Russian Taimyr Peninsula) form, with those of northern North America, a coherent “Nearctic-Arctic” biogeographic cluster. This cluster is distinct from that of “Northern and Alpine Europe”. Few, if any, Arctic tardigrades survived Pleistocene glaciation in situ amongst ice-free refugia. Similarly, few/none moved south ahead of the advancing ice-cap into the deglaciated Palaearctic and Nearctic and subsequently returned north during the Holocene deglaciation. It is more probable that most Arctic tardigrades are derived from wind-blown Nearctic propagules that colonized the region during the Holocene.