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

Sculpin fishes belonging to the family Cottidae represent a large and complex group, inhabiting a wide range of freshwater, brackish-water, and marine environments. Numerous studies based on analysis of their morphology and genetic makeup frequently provided controversial results. In the present work, we sequenced complete mitochondrial (mt) genomes and fragments of nuclear ribosomal DNA (rDNA) of the fourhorn sculpinMyoxocephalus quadricornisand some related cottids to increase the power of phylogenetic and taxonomic analyses of this complex fish group. A comparison of theMy. quadricornismt genomes obtained by us with other complete mt genomes available in GenBank has revealed a surprisingly low divergence (3.06 +/- 0.12%) withMegalocottus platycephalusand, at the same time, a significantly higher divergence (7.89 +/- 0.16%) with the species of the genusMyoxocephalus. Correspondingly, phylogenetic analyses have shown thatMy. quadricornisis clustered withMe. platycephalusbut not with theMyoxocephalusspecies. Completely consistent patterns of divergence and tree topologies have been obtained based on nuclear rDNA. Thus, the multi-gene data in the present work indicates obvious contradictions in the relationships between theMyoxocephalusandMegalocottusspecies studied. An extensive phylogenetic analysis has provided evidence for a closer affinity ofMy. quadricorniswith the species of the genusMegalocottusthan with the species of the genusMyoxocephalus. A recombination analysis, along with the additional GenBank data, excludes introgression and/or incorrect taxonomic identification as the possible causative factors responsible for the observed closer affinity between the two species from different genera. The above facts necessitate realignment of the generaMyoxocephalusandMegalocottus. The genetic data supports the two recognized genera,MyoxocephalusandMegalocottus, but suggests changing their compositions through transferringMy. quadricornisto the genusMegalocottus. The results of the present study resolve the relationships within a complex group of sculpin fishes and show a promising approach to phylogenetic systematics (as a key organizing principle in biodiversity research) for a better understanding of the taxonomy and evolution of fishes and for supplying relevant information to address various fish biodiversity conservation and management issues.