Opening a can of worms: unprecedented sympatric cryptic diversity within British lumbricid earthworms

Abstract

Earthworms play a major role in many aspects of soil fertility, food web ecology and ecosystem functioning, and hence are frequently the subjects of, for example, ecological and toxicological research. Our aim was to examine the genetic structure of common earthworm species, to identify cryptic lineages or species that may be distinct ecotypes or biotypes (and hence confound current research based upon morphotypes) and to try to explain the massive cryptic diversity that eventually emerged. We demonstrated that species such as Allolobophora chlorotica, Aporrectodea longa, Aporrectodea rosea and Lumbricus rubellus all comprise highly divergent lineages with species-level divergence at the mitochondrial cytochrome oxidase I (COI) gene. In Allo. chlorotica alone, we found 55 haplotypes for COI, with 35 of these being found in pink and 20 in green morph worms. There were no cases of the two colour morphs sharing COI haplotypes. Phylogenetic analyses of mitochondrial COI and 16S genes showed the presence of five highly divergent lineages, suggesting the presence of multiple cryptic species within Allo. chlorotica. There was no clear geographical pattern to lineage distribution and many populations were polymorphic for both mitochondrial DNA lineage and colour morph. Amplified fragment length polymorphism results, based on two primer combinations, were broadly congruent with mitochondrial DNA results with one significant exception. Despite showing over 14% divergence at COI, amplified fragment length polymorphism markers showed that the two green morph lineages may be interbreeding and therefore represent a single taxon. The cryptic diversity revealed by these results has profound consequences for all areas of earthworm research.

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

“…Some of these taxonomic difficulties may be alleviated by recent developments in imagery for the description of internal morphology using Micro-Computed Tomography (Fernández et al 2014), but lack of taxonomic expertise remains limiting. In recent years, the introduction of DNA barcoding has effectively aided species discrimination, identification of new taxa, reconstruction of phylogeny, and biodiversity assessments in numerous invertebrate groups, including earthworms (King et al 2008;Chang & James 2011;Decaëns et al 2013). DNA barcoding can be particularly useful for resolving previous taxonomic confusion but also to accelerate new taxonomic acts.…”

High mitochondrial DNA sequence diversity in the parthenogenetic earthworm Dendrobaena octaedra

“…These haplotypes were basal to or in a polytomy with the more common haplotypes (Figure 3, groups B-D). Regardless of their divergence relative to clade A, the entire data set had divergence of only 3% (see Supplementary Material), which is within expectations of within species divergence in lumbricids (see King et al, 2008). Surprisingly, the COI sequence from D. attemsi was identical to D. octaedra haplotypes and fell well within the D. octaedra clade.…”

“…Distances between haplotypes based on the Kimura two-parameter (K2P) þ g model were also calculated (using MEGA). Although the K2P model is not expected to be a good match to our data set, we chose to also use these distances for comparison to DNA bar-coding studies, which are typically based on K2P or even simpler models (for example, Hebert et al, 2003;King et al, 2008).…”

“…A recent focus on applying molecular genetic tools to study earthworm populations (for example, Heethoff et al, 2004;Pérez-Losada et al, 2005;King et al, 2008;Dupont, 2009) has raised the possibility that cryptic species may be more common within the Lumbricidae than previously thought. Indeed, King et al (2008) identified at least four independent lineages within Allolobophora chlorotica alone, as well as potentially multiple lineages of Aporrectodea longa, Apo. rosea and Lumbricus rubellus from only a small sample of worms from the UK.…”

“…Identification of cryptic diversity is complicated by similar morphologies observed among lumbricids and calls for further use of molecular tools in identifying biodiversity (Dupont, 2009). DNA bar-coding efforts have indicated that such tools are useful in this regard, with between-species divergences in the range of 13-18% for earthworms (Huang et al, 2007;King et al, 2008;Chang et al, 2009).…”