Evolutionary relationships among squids of the family Gonatidae (Mollusca: Cephalopoda) inferred from three mitochondrial loci

DNA barcoding for squids of the family Gonatidae (Cephalopoda: Teuthida) from the boreal North Pacific

A fragment of cytochrome c oxidase I was used to assess whether species of the squid family Gonatidae from the North Pacific could be identified using DNA barcoding approach. Pairwise intra- and interspecific p-distances were assessed, and systematic relationships among species were estimated by NJ analysis. Examined species formed well-differentiated species-specific clades on the neighbor-joining and Bayesian trees. Multiple taxa formed clades supported by both tree topologies and species hypothesis-free ABGD method. Species morphologically identified as Gonatus tinro and Gonatopsis okutanii demonstrated intraspecific level of molecular genetic divergence (0.2-0.3%) indicating that they are conspecific. Genetic differences between the G. berryi clade and a squid morphologically close to that species may indicate a new cryptic species. High levels (>6.2%) of genetic differentiation within B. borealis suggested the existence of two cryptic species. This study confirms the usefulness of DNA barcoding for identifying species as well as discovering cryptic diversity in the gonatid squids, and indicates the need for further deeper insights into the phylogeny of the Gonatidae.

Phylogenetic relationships among the family Ommastrephidae (Mollusca: Cephalopoda) inferred from two mitochondrial DNA gene sequences

Squids of the family Ommastrephidae are distributed worldwide, and the family includes many species of commercial importance. To investigate phylogenetic relationships among squid species of the family Ommastrephidae, partial nucleotide sequences of two mitochondrial gene loci (cytochrome c oxidase subunit I [1277bp] and 16S rRNA [443bp]) of 15 ommastrephid species and two outgroup species from the families Loliginidae and Enoploteuthidae were determined and used to construct parsimony and distance based phylogenetic trees. The molecular data provided several new phylogenetic inferences. The monophyletic status of three subfamilies (Illicinae, Todarodinae and Ommastrephinae) was well supported, although phylogenetic relationships between the subfamilies were not resolved. Inclusion of a problematic species, Ornithoteuthis volatilis, to Todarodinae was indicated. Within Todarodinae, the Japanese common squid Todarodes pacificus was observed to have much closer relationship to the species of the genus Nototodarus than to its congener (Todarodes filippovae). These results indicate that re-evaluation of several morphological key characters for ommastrephid taxonomy may be necessary.

DNA barcoding analysis of Coleoidea (Mollusca: Cephalopoda) from Chinese waters

Coleoids are part of the Cephalopoda class, which occupy an important position in most oceans both at an ecological level and at a commercial level. Nevertheless, some coleoid species are difficult to distinguish with traditional morphological identification in cases when specimens are heavily damaged during collection or when closely related taxa are existent. As a useful tool for rapid species assignment, DNA barcoding may offer significant potential for coleoid identification. Here, we used two mitochondrial fragments, cytochrome c oxidase I and the large ribosomal subunit (16S rRNA), to assess whether 34 coleoids accounting for about one-third of the Chinese coleoid fauna could be identified by DNA barcoding technique. The pairwise intra- and interspecific distances were assessed, and relationships among species were estimated by NJ and bayesian analyses. High levels of genetic differentiation within Loliolus beka led to an overlap between intra- and interspecific distances. All remaining species forming well-differentiated clades in the NJ and bayesian trees were identical for both fragments. Loliolus beka possessed two mitochondrial lineages with high levels of intraspecific distances, suggesting the occurrence of cryptic species. This study confirms the efficacy of DNA barcoding for identifying species as well as discovering cryptic diversity of Chinese coleoids. It also lays a foundation for other ecological and biological studies of Coleoidea.