Underground evolution: New roots for the old tree of lumbricid earthworms

Abstract

Earthworms belonging to the family Lumbricidae are extremely abundant in terrestrial temperate regions. They affect soil properties and nutrient cycling, thus shaping plant community composition and aboveground food webs. Some lumbricids are also model organisms in ecology and toxicology. Despite the intense research efforts dedicated to lumbricids over the last 130 years, the evolutionary relationships and taxonomic classification of these organisms are still subject to great debate. Resolution of their systematics is hampered by the structural simplicity of the earthworm body plan and the existence of cryptic species. We sampled 160 earthworm specimens belonging to 84 lumbricid species (28 genera) and 22 Lumbricoidea outgroups, sequenced two nuclear genes, four mitochondrial genes and seven mitochondrial tRNAs and examined 22 morphological characters. We then applied a combination of phylogenetic methods to generate the first robust genus-level phylogeny of the Lumbricidae. Our results show that the current Lumbricidae classification and the underlying hypotheses of character evolution must be revised. Our chronogram suggests that lumbricids emerged in the Lower Cretaceous in the holarctic region and that their diversification has been driven by tectonic processes (e.g. Laurasia split) and geographical isolation. Our chronogram and character reconstruction analysis reveal that spermathecae number does not follow a gradual pattern of reduction and that parthenogenesis arose from sexual relatives multiple times in the group; the same analysis also indicates that both epigeic and anecic earthworms evolved from endogeic ancestors. These findings emphasize the strong and multiple changes to which morphological and ecological characters are subjected, challenging the hypothesis of character stasis in Lumbricidae.

Earthworms and Vermicomposting

“…Phylogenetic analysis of maximum parsimony, maximum likelihood, and Bayesian (BMCMC) of the sequences of genes 28S and cytochrome c oxidase I (COI) and of the combined sequences (28S-COI) showed E. fetida and E. andrei to be monophyletic [18]. These results have been confirmed by other authors and by our group in a genus-level phylogeny of the family Lumbricidae (see Figures 7 and 8, [17]) and through a DNA barcoding study [19].…”

“…Although the names are often considered synonyms, Dendrobaena hortensis and Dendrobaena veneta are actually phylogenetically different species (see Figure 8; [17]). Dendrobaena veneta is two times larger (50-150 mm) than D.…”

Molecular identification and distribution of native and exotic earthworms in New Zealand human-modified soils

“…Chang & Chen 2005;Minamiya et al 2009) as well as discriminating between native and exotic species (Cameron et al 2008;. In conjunction with phylogenetic analyses, DNA barcoding analyses not only contribute to the discovery of new species and the identification of specimens, but also enhance our understanding of earthworms' ecology, taxonomy and evolutionary history (Domínguez et al 2015).…”

The Allolobophora sturanyi species group revisited: Integrated taxonomy and new taxa (Clitellata: Megadrili)

“…The closer relationship of Aporrectodea dubiosa (Örley, 1881) and Aporrectodea molleri (Rosa, 1889) was yet observed (Pop et al 2005) and here they grouped together with the other Aporrectodea species (clade e) unlike to the trees in Domínguez at al. (2015) where they formed a clade with Allolobophora chlorotica (Savigny, 1826) (type species of the genus).…”

“…This BalkanicCentral European clade of the Allolobophora species has already been recognized by Pop et al (2005) and more recently in Domínguez et al (2015). This clade (a here, and c in Domínguez et al 2015) contains species relegated previously into different genera by Mršić (1991) i.e. Cernosvitovia (opisthocystis, rebeli, dudichi), Karpatodinariona (dacica, dacidoides, sturanyi), Serbiona (mehadiensis, robusta) and Alpodinaridella (gestroides, gestroi).…”