DNA barcodes for species identification of euphausiids (Euphausiacea, Crustacea)

Many species of euphausiids (Euphausiacea, Crustacea) are distinguished by subtle or geographically variable morphological characters, and erroneous identification of euphausiid species may be more frequent than currently acknowledged. DNA barcodes (short DNA sequences that discriminate species and aid in recognition of unknown species) are of use for this group. A 650 bp region of mitochondrial cytochrome oxidase I (mtCOI) was sequenced for 40 species of 10 euphausiid genera: Bentheuphausia, Euphausia, Meganyctiphanes, Nematobrachion, Nematoscelis, Nyctiphanes, Stylocheiron, Tessarabrachion, Thyssanoessa and Thysanopoda. mtCOI sequence variation discriminated all species; pairwise differences averaged 16.4% (range 7‐24%); mean generalized time reversible (GTR) genetic distance was 26.7%. mtCOI reliably identified euphausiid species: variation within species was typically ,1% and GTR distance was typically ,2%. Atlantic and Pacific Ocean populations of Euphausia brevis differed by 13% (GTR genetic distance ¼ 28%) and may deserve status as distinct species. mtCOI gene trees were reconstructed for five genera using maximum parsimony, maximum likelihood and Bayesian algorithms; best-fit models of nucleotide evolution were determined for each genus. The mtCOI gene tree for 20 species of Euphausia reproduced one of three morphologically defined species groups. mtCOI resolved relationships among closely related species of most genera, usually in accord with morphological groupings. A comprehensive DNA barcode database for euphausiids will help ensure accurate species identification, recognition of cryptic species and evaluation of taxonomically meaningful geographic variation.