Development and evaluation of a DNA-barcoding approach for the rapid identification of nematodes

Free-living nematodes are abundant in all marine habitats, are highly diverse, and can be useful for monitoring anthropogenic impacts on the environment. Despite such attributes, nematodes are effectively ignored by many marine ecologists because of their time-consuming taxonomy. Nematode diagnostics has traditionally relied on detailed comparison of morphological characters which, given their abundance, is difficult and laborious, meaning that the biodiversity of the group is typically underestimated. Molecular methods such as DNA-barcoding offer potentially efficient alternative approaches to studying the biodiversity of marine nematode communities, allowing these organisms to be more effectively exploited in ecological surveys and environmental assessments. In this study, a number of nuclear and mitochondrial genomic regions were evaluated as potential diagnostic loci for marine nematode species identification. Of these, the 18S ribosomal RNA gene amplified most reliably from a range of taxa, and was therefore evaluated as a DNA barcode. In a comparison of molecular and morphological identifications, over 97% of specimens sequenced were correctly assigned on the basis of a short stretch of 18S rRNA sequence (approximately 345 bp), making this a potentially useful marker for the rapid molecular assignment of unknown nematode species, and evaluation of nematode species richness during ecological surveys or environmental assessments. This study showed that a single marker approach based on amplification and sequencing may prove invaluable in the rapid identification of nematodes during ecological surveys and, indeed, other taxonomically challenging invertebrate taxa.