Living on the edge: Pleistocene ice‐free refugia and collared lemming ( <i>Dicrostonyx</i> sp.) in the North American High Arctic

Collared lemmings (genus Dicrostonyx ) are an emblematic group of Arctic‐tundra mammalian communities, comprising six different species in North America. As other northern fauna, most of their diversity is impacted by Pleistocene glacial–interglacial cycles. While D. hudsonius and D. richardsoni have a restricted distribution area on both sides of the Hudson Bay, D. groenlandicus is widespread in all Nearctic northernmost regions, from Alaska and Canadian mainland to the High Arctic Archipelago and Greenland, occupying a highly fragmented area. Using extensive data, this paper investigates the morphological variability of the molar of Nearctic Dicrostonyx using geometric morphometrics. Our results show weak interspecific differences among Nearctic Dicrostonyx , while demonstrating the existence of a clear geographical structure: a north–south gradient that structures collared lemming's phenotype, surpassing interspecific differences. The possible causes of such patterns are explored, whether they are environmental (e.g. due to local to regional climatic conditions) or phylogeographic (e.g. isolation of the populations during the glacial periods) using ERA5‐Land reconstruction climatic data, and a reconstruction of the Laurentide Ice Sheet extent with isometric variations. The peculiar status of several populations, including Greenland and Victoria Island specimens, can be linked with their survival and isolation in Pleistocene ice‐free refugia in the High Arctic in agreement with both genetic and morphological signals. We argue that studying present‐day morphological variability can provide meaningful information on the Quaternary biogeography of modern species.