Distribution and phylogeny of glacier ice worms (Mesenchytraeus solifugus and Mesenchytraeus solifugus rainierensis)

Abstract

Glacier ice worms, Mesenchytraeus solifugus (Emery, 1898) and Mesenchytraeus solifugus rainierensis Welch, 1916 (Enchytraeidae), are the only known oligochaetes adapted to life in ice. We have collected ice worm specimens from over 100 populations throughout the Pacific northwestern region of North America. Their current range extends ~2500 km along the Pacific coastline between south-central Alaska and central Oregon, with most populations occurring on relatively low-elevation, temperate glaciers. Phylogenetic analyses utilizing partial nuclear 28S rDNA and mitochondrial cytochrome c oxidase subunit I (COI) loci revealed the presence of two geographically distinct clades (northern and southern). The northern clade comprises all Alaskan populations, while the southern clade contains British Columbia, Washington State, and Oregon State populations. No evidence of gene flow was detected between these two lineages or between noncontiguous glaciers throughout their geographic range. Our results suggest that the mechanism of ice worm dispersal is primarily active, though at least one episode of passive dispersal is noted at the southern extent of their range.