The disjunct distribution of relict earthworm genera clarifies the early historical biogeography of the Lumbricidae (Crassiclitellata, Annelida)

Abstract

The historical biogeography of the Lumbricidae, the main Palearctic earthworm family, may be linked to the paleogeography of their putative ancestral range in Iberia–southeastern France–Corsica–Sardinia. Although molecular phylogenetics has recently been used to analyze most endemic genera in this area, the genus Kritodrilus has not yet been studied. The generotype Kritodrilus calarensis and other closely related species inhabit southeastern France. However, other species from the Iberian Peninsula (e.g., Kr. osellai) have been assigned to Kritodrilus, the same for the Vindobonic (Hungarian–Austrian–Czech–Slovakian) Dendrobaena mrazeki. In order to unravel the paleobiogeographic, evolutionary, and taxonomic significance of Kritodrilus, the aforementioned species (and three potential relatives) were sequenced for seven molecular markers. Molecular phylogenetic inference recovered a clade of French Kritodrilus (including Et. setusmontanus) closely related to the Northwestern Iberian Galiciandrilus and Compostelandrilus, the latter being a sister clade to the Vindobonic species (described as a new genus). Time-calibrated phylogenetic inference estimated that these three clades diverged around 55 Ma. Ecological niche models for these clades were mainly influenced by the same environmental variables, but showed non-overlapping highly suitable areas (except for Kritodrilus). Ancestral area reconstruction inferred the origin of the Lumbricidae in Corsica–Sardinia and the Iberian Peninsula, with eventual expansion eastwards toward France, Central Europe, and the Carpato-Balkanic area. For Kritodrilus and its relatives, this expansion may have been contemporaneous with the Paleocene–Eocene thermal maximum. Later climatic changes may explain the strikingly disjunct ranges. This work highlights the evolutionary and biogeographic significance of these isolated earthworm lineages and the importance of their preservation.