Contrasting phylogeographic patterns of earthworms (Crassiclitellata, Lumbricidae) on near-shore mediterranean islands.

Abstract

Comparative phylogeography is a powerful methodological approach to understand the particular evolutionary phenomena that occur in islands. This method has been rarely applied to insular earthworm communities. These soil animals show a striking dichotomy in their phylogeographic patterns: deeply divergent, regionally structured linages and widely distributed, genetically homogeneous lineages. An intensive earthworm sampling campaign in the Southern France archipelago of Hyères served as an opportunity to check for the existence of these patterns in the framework of a near-shore, continental archipelago. Molecular barcoding (COI sequencing) was performed for earthworm communities of 31 localities, and the seven with more informative distributions were chosen for phylogenetic inference and genetic diversity evaluation. A time-calibrated phylogeny was obtained to estimate a temporal framework for colonization and divergence within the islands, and haplotype networks were used to visualize relationships between populations in detail. Four species (Allolobophora chlorotica, Aporrectodea nocturna, Scherotheca cf. dugesi and Scherotheca rhodana) showed clades restricted to the archipelago and hints of Plio-Pleistocene in situ divergence. The other three species (Aporrectodea rosea, Aporrectodea trapezoides and Eiseniella tetraedra) lacked geographic structure, being nested in clades with individuals from distant countries; their arrival to the archipelago appeared consistent with human-mediated introduction. These contrasting phylogeographic patterns are discussed in the context of paleogeographic events affecting the Mediterranean in the Late Tertiary-Quaternary and biological traits of earthworms, with biparental sexual vs parthenogenetic reproduction as the main factor explaining them.