Genotyping of Black Sea trematodes of the family Opecoelidae by mitochondrial markers

Opecoelidae Ozaki, 1925 (Trematoda: Opecoeloidea) is the biggest trematode family in the Black Sea in terms of species and genera number. Maritae of the most common Black Sea Opecoelidae trematodes are well described morphologically; nevertheless, information on their genomes structure is sketchy, and data on mitochondrial genomes are absent. The aim was to study the structure of mitochondrial genome fragments of Black Sea trematode species: Cainocreadium flesi Korniychuk & Gaevskaya, 2000, Gaevskajatrema perezi (Mathias, 1926) Gibson & Bray, 1982, and Helicometra fasciata (Rudolphi, 1819) Odhner, 1902. Sequences were made for CO1 (the cytochrome c oxidase subunit I) and 16S mitochondrial genes. To amplify CO1 gene fragment of Cainocreadium and Helicometra trematodes, primers were developed. Phylogenetic relationships within the analyzed part of the Opecoelidae family were reconstructed on the basis of our data and the corresponding GenBank data by the Maximum Likelihood estimation and the MEGA X programme. To root the phylogenetic trees, the corresponding sequences of the closely related trematode Brachycladium goliath (Brachycladioidea: Brachycladiidae) were used. For the first time, nucleotide sequences of CO1 and 16S mitochondrial genes fragments of Black Sea trematodes C. flesi, G. perezi, and H. fasciata from different definitive fish hosts were determined and deposited in the GenBank. In case of C. flesi, no host-specific lines were found in the structure of CO1 mitochondrial gene fragment, but high CO1 nucleotide diversity was noted. Black Sea H. fasciata, parasitizing peacock wrasse, Symphodus tinca, were revealed to be a host-specific CO1 haplogroup; its taxonomical status requires further clarification, and ecological and genetic studies of the putative H. fasciata species complex from different water areas are needed. No host-specific genetic lines were found when analyzing the sequences of H. fasciata 16S rRNA mitochondrial gene fragment. No significant differences in 16S fragment were registered between G. perezi trematodes from different Black Sea definitive hosts; however, the intraspecific 16S nucleotide diversity was rather high.