Mitochondrial DNA and morphological variation in the sentinel earthworm species Lumbricus rubellus

• We investigated possible lineage-specific morphological traits in Lumbricus rubellus
• We performed a widespread mitochondrial analysis of British L. rubellus populations.
• A new trait was found to be effective in differentiating lineages of L. rubellus.
• The two lineages of L. rubellus were found to be widespread and often co-occurring.

The common epigeic earthworm Lumbricus rubellus has been found to comprise two genetically distinct lineages and this genetic heterogeneity could compromise its currently widespread use as a sentinel in soil ecotoxicology. An extensive analysis of lineage diversity was conducted on UK populations of L. rubellus, comprising 137 individuals collected from England and Wales. Sequencing of the mitochondrial COI region revealed the widespread occurrence of the two described lineages throughout Britain, which were often found to co-exist at the same site. Morphological characters were investigated to differentiate the two lineages. A rapid genetic test (mitochondrial PCR amplification and restriction digestion) was applied to determine the lineage of each specimen. A blind trial revealed a characteristic glandular tumescence to be effective in differentiating the lineages, particularly in identifying ‘lineage B’ worms. COI sequence analysis was also conducted upon three other Lumbricus species, which failed to uncover any genetic lineages comparable to those found within L. rubellus.