Winterfell survivor: The European phylogeography of a riparian earthworm (Annelida, Clitellata)

Abstract

Although some earthworms can survive in permafrost and tolerate cold conditions, it is generally believed that most earthworms were eradicated from northern latitudes during the Last Glacial Maximum. The main goal of this study is to test this hypothesis using a cosmopolitan earthworm as model, Eiseniella tetraedra. We collected 1640 specimens in 294 localities from 19 different countries. We examined three molecular markers (COI, 16S and 28S) and their morphology. Furthermore, we investigated their potential niches through Species Distribution Models. Eleven genetic lineages were found, nested in five clades. Clade I was more prevalent in cold biogeographical regions such as the Continental, the Atlantic or even the Arctic, while clade II was prevalent in Mediterranean regions. Potential niches agreed with the distribution trends. The presence of restricted clades in the Iberian and Scandinavian peninsulas, as well as in Eastern Europe, suggests that these three regions served as refugia during the Last Glacial Maximum. Thus, nunatak and tabula rasa hypotheses were necessary to explain the actual distribution of this riparian earthworm.