Abstract
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 sculpin Myoxocephalus quadricornis and some related cottids to increase the power of phylogenetic and taxonomic analyses of this complex fish group. A comparison of the My. quadricornis mt genomes obtained by us with other complete mt genomes available in GenBank has revealed a surprisingly low divergence (3.06 ± 0.12%) with Megalocottus platycephalus and, at the same time, a significantly higher divergence (7.89 ± 0.16%) with the species of the genus Myoxocephalus. Correspondingly, phylogenetic analyses have shown that My. quadricornis is clustered with Me. platycephalus but not with the Myoxocephalus species. 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 the Myoxocephalus and Megalocottus species studied. An extensive phylogenetic analysis has provided evidence for a closer affinity of My. quadricornis with the species of the genus Megalocottus than with the species of the genus Myoxocephalus. 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 genera Myoxocephalus and Megalocottus. The genetic data supports the two recognized genera, Myoxocephalus and Megalocottus, but suggests changing their compositions through transferring My. quadricornis to the genus Megalocottus. 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.
Highlights
The genus Myoxocephalus Tilesius 1811 comprises 15 or 16 species [1,2,3,4] distributed widely from the northern Pacific and Arctic Oceans to the northern Atlantic Ocean [5,6,7,8,9]
Morpho-anatomical [5,6,14,15] and genetic [16,17,18,19] studies have shown that the genus Myoxocephalus is closely related to the genus Megalocottus Gill 1861 represented by the only species, the belligerent sculpin Megalocottus platycephalus (Pallas 1814)
Mitochondrial DNA markers [20] have revealed a genetic heterogeneity associated with the spatial distribution of the species which might result in the emergence of two subspecies known for Me. platycephalus: Me. p. platycephalus
Summary
The genus Myoxocephalus Tilesius 1811 comprises 15 or 16 species [1,2,3,4] distributed widely from the northern Pacific and Arctic Oceans to the northern Atlantic Ocean [5,6,7,8,9] Members of this genus have diverse morphologies but are clearly differentiated from other taxa in the family Cottidae [5,6,10,11,12,13]. Morpho-anatomical [5,6,14,15] and genetic [16,17,18,19] studies have shown that the genus Myoxocephalus is closely related to the genus Megalocottus Gill 1861 represented by the only species, the belligerent sculpin Megalocottus platycephalus (Pallas 1814). Further genetic studies confirmed the Yabe’s [13] classification [19,21,22], except Argyrocottus, which still remains unstudied by genetic methods
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