Genetic diversity of the earthworm Eisenia nordenskioldi (Lumbricidae, Annelida)

Abstract

Eisenia nordenskioldi (Eisen, 1879) is the most widespread earthworm species in Siberia. It inhabits a wide range of habitats, from tundra to forest steppe, and is characterized by high morphological, ecological, and karyotypic diversity. E. nordenskioldi is usually divided into two subspecies, the pigmented E. n. nordenskioldi and the unpigmented E. n. pallida; a set of Eisenia species with a close diagnosis was also isolated from E. nordenskioldi in the last fifty years. This high diversity makes this species a promising model for studying earthworm speciation and evolution. In this study, we review all available information on the genetic and ecological diversity of E. nordenskioldi, including our published and unpublished data, as well as studies of other authors. We demonstrate that each subspecies of E. nordenskioldi (E. n. nordenskioldi and E. n. pallida) can be divided into several genetic lineages based on differences in mitochondrial and nuclear DNA. The studied lineages diverged several million years ago, and population groups within each lineage, hundreds of thousands years ago. We report distributions and genetic patterns for each of the detected genetic lineages. Subspecies E. n. nordenskioldi and E. n. pallida are most probably non-monophyletic, and the pigmentation character is labile and possibly independently evolved in different lineages. We also propose hypotheses on the interplay of its observed genetic diversity with morphological and ecological variation, as well as on the relationships of E. nordenskioldi with certain species of the genus Eisenia. Based on the available information, we attempt to present a general outlook on E. nordenskioldi genetic structure and further directions of its study.