Genetic Evidence for a Mixed Composition of the Genus Myoxocephalus (Cottoidei: Cottidae) Necessitates Generic Realignment

Evaluation of Differences between the Baltic Triglopsis quadricornis and White Sea Triglopsis sp. Using Morphological and Genetic Data

According to the modern fish system, one species of fourhorn sculpin Triglopsis quadricornis lives in the Baltic Sea and Arctic waters. In the present study, sculpins from the Baltic and White Seas were studied using different methods: morphological analysis to establish patterns of the seismosensory system, tomography for the study of cranial bones, X-ray imaging for the study of the axial skeleton, as well as phylogenetic analysis of two mtDNA markers (control region and CO1) and one nDNA marker (RAG1). The results obtained by these methods were used to prove the existence of two species: T. quadricornis in the Baltic Sea and Triglopsis sp. in the White Sea. These species differ significantly in the unique shape and size of the bony outgrowths on the head, as well as in the number of bony plates on the body. Genetic differences between the species were expressed in the formation of T. quadricornis and Triglopsis sp. independent clusters on Bayesian phylogenetic trees reconstructed based on the sequences of the mtDNA control region and RAG1.

Recombinant Mitochondrial Genomes Reveal Recent Interspecific Hybridization between Invasive Salangid Fishes

The interspecific recombination of the mitochondrial (mt) genome, if not an experimental artifact, may result from interbreeding of species with broken reproductive barriers, which, in turn, is a frequent consequence of human activities including species translocations, habitat modifications, and climate change. This issue, however, has not been addressed for Protosalanx chinensis and other commercially important and, simultaneously, invasive salangid fishes that were the product of successful aquaculture in China. To assess the probability of interspecific hybridization, we analyzed the patterns of diversity and recombination in the complete mitochondrial (mt) genomes of these fishes using the GenBank resources. A sliding window analysis revealed a non-uniform distribution of the intraspecific differences in P. chinensis with four highly pronounced peaks of divergence centered at the COI, ND4L-ND4, and ND5 genes, and also at the control region. The corresponding divergent regions in P. chinensis show a high sequence similarity (99−100%) to the related salangid fishes, Neosalanx tangkahkeii and N. anderssoni. This observation suggests that the divergent regions of P. chinensis may represent a recombinant mitochondrial DNA (mtDNA) containing mt genome fragments belonging to different salangid species. Indeed, four, highly significant (pairwise homoplasy index test, P < 0.00001) signals of recombination have been revealed at coordinates closely corresponding to the divergent regions. The recombinant fragments are, however, not fixed, and different mt genomes of P. chinensis are mosaic, containing different numbers of recombinant events. These facts, along with the high similarity or full identity of the recombinant fragments between the donor and the recipient sequences, indicate a recent interspecific hybridization between P. chinensis and two Neosalanx species. Alternative hypotheses, including taxonomical misidentifications, sequence misalignments, DNA contamination, and/or artificial PCR recombinants, are not supported by the data. The recombinant fragments revealed in our study represent diagnostic genetic markers for the identification and distinguishing of hybrids, which can be used to control the invasive dynamics of hybrid salangid fishes.

The subfamily Myoxocephalinae of cottid fishes (Cottidae): Genetic divergence and phylogenetic relationships

A comprehensive study based on molecular marker and karyotype analyses has provided evidence for the monophyly of the subfamily Myoxocephalinae, which includes the genera Myoxocephalus, Megalocottus, Microcottus, Porocottus, Enophrys and Argyrocottus. In addition, the karyotype of the threadfoot sculpin Argyrocottus zanderi Herzenstein 1892 has been studied for the first time. Marker traits of karyotypes identified 13 species among six cottid genera. As the molecular genetic results confirmed, the subfamily is divided into two groups corresponding to Enophrys and Myoxocephalus. The molecular genetic data did not support the formation of tribes within the subfamily Myoxocephalinae, as proposed earlier based on morphological characters. Moreover, the genera Trichocottus and Taurocottus should be excluded from the Myoxocephalinae. The evolutionary transformations of karyotypes in cottid fish tended towards a reduction in the number of chromosomes and chromosome arms.