The infraorder Zoarcales (Cottoidei), or eelpouts, includes about 400 species of coldwater fishes concentrated mainly in the North Pacific. To date, the molecular phylogenetic methods in combination with morphological data have significantly contributed to understanding the taxonomic composition of this group and made it possible to confirm/refute validity of some families of obscure origin. In spite of the growing amount of new data on taxonomy and evolution of eelpouts, a consideration of the original and independent data is obviously needed to verify the existing knowledge of this taxon. In this study, which is based on concatenated matrix of Co-1 and Cyt-b mitochondrial genes, as well as relying on the samples from seven families and 45 species of eelpouts, we have reconstructed the phylogeny, which is generally consistent with previous inferences. Despite the resolution of the original data matrix is low, we have demonstrated the monophyletic origin of the families Zoarcidae and Anarhichadidae, as well as Neozoarcidae, previously related to Stichaeidae and recently revised Eulophiidae. The polyphyletic patterns amongst some subfamilies in Stichaeidae have been confirmed, whereas Opisthocentrinae and Pholidae seem to constitute a valid family-level taxon. Our results provide new opportunities with respect to taxonomic relationships in the complex and diverse group of eelpouts , whose part in the tree of life is not covered by recently flourishing multilocus phylogeny of teleost fishes. In light of the data obtained, the necessity of more unified and reproducible approaches to resolve the issues of evolution and taxonomy of such a complex group as Zoarcales becomes more evident.
The analysis of variation among 203 nucleotide sequences of Co-1 gene (DNA-barcode) for 45 species, 31 genera and 7 families of the order Perciformes from the Far Eastern seas of Russia has been performed. As a result, 42 species (93.3%) can be unambiguously identified using molecular DNA-barcode at Co-1, whereas more variable markers are required for other species (6.7%): Stichaeus grigorjewi, S. nozawae, and Lumpenus sagitta. The latter includes as well 2 morphologically distinct (by number of vertebrae) but genetically unresolved species, L. sagitta (Sea of Okhotsk) and L. fabricii (Bering Sea). In addition, within this genus morphologically poorly characterized but genetically well-distinguished cryptic species has been detected. Amphi-Pacific distribution is in question relative to L. sagitta. Cryptic diversity was observed in the genus Ammodytes.
A total of 95 nucleotide sequences of a Co 1 gene fragment of approximately 650 bp were analyzed for fishes of the orders Perciformes and Scorpaeniformes (outgroup). Gene trees based on four algorithms (BA, NJ, MP, and ML) were similar in topology of solved branches. An emphasis was placed on the species and generic levels, but a significant phylogenetic signal was obtained for higher taxonomic ranks as well. For instance, a monophyletic origin was confirmed for the family Zoarcidae and the subfamily Opisthocentrinae (Stichaeidae). The proportion of different nucleotides in the sequences compared (p distances) significantly increased with increasing taxonomic rank. The p distances were estimated for four hierarchic levels and were (1) 0.15 ± 0.06% for the within species hierarchic level, (2) 6.33 ± 0.37% for the within genus level, (3) 11.83 ± 0.06% for the within family level, and (4) 15.22 ± 0.05% for the within order level. The difference in the Co 1 gene fragments between levels (1) and (2) allows almost errorless species identification on the basis of this kind of a molecular bar code.
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