Identifying earthworms through DNA barcodes

Abstract

With almost 3000 species, earthworms provide important model systems for studying soil fauna. However, species identification of earthworms is difficult and therefore limiting. The use of DNA barcodes, which are short sequences from standardized regions of the genome, has been regarded as a promising approach to resolve this taxonomic dilemma. We evaluated sequence diversity in the mitochondrial cytochrome- c oxidase I (COI) gene as a tool for resolving differences among species of Chinese earthworms. Members of six genera and 28 species were examined, and species were successfully discriminated in all cases. Sequence divergence within species was generally less than 1%, whereas divergence between species was greater than 15% in all cases. Divergence among individuals of Eisenia fetida were much higher (up to 7.8%); however, this may represent the presence of unrecognized sibling species or subspecies. We conclude that although it cannot completely replace taxonomy, the DNA barcode is a powerful tool for identifying species of earthworms and provides a useful complement to traditional morphological taxonomy.