Biological identifications through DNA barcodes: the case of the Crustacea

The ability of a 650 base pair section of the mitochondrial cytochrome c oxidase I (COI) gene to provide species-level identifications has been demonstrated for large taxonomic assemblages of animals such as insects, birds, and fishes, but not for the subphylum Crustacea, one of the most diverse groups of arthropods. In this study, we test the ability of COI to provide identifications in this group, examining two disparate levels in the taxonomic hierarchy - orders and species. The first phase of our study involved the development of a sequence profile for 23 dominant crustacean orders, based upon the analysis of 150 species, each belonging to a different family. The COI amino acid data placed these taxa into cohesive assemblages whose membership coincided with currently accepted boundaries at the order, superorder, and subclass levels. Species-level resolution was subsequently examined in an assemblage of Decapoda and in representatives of the genera Daphnia (Cladocera) and Gammarus (Amphipoda). These studies revealed that levels of nucleotide sequence divergence were from 19 to 48 times greater between congeneric species than between individuals of a species. We conclude that sequence variation in the COI barcode region will be very effective for discriminating species of Crustacea.