Phylogenetic Study Of Flatfish (Order: Pleuronectiformes) From China Based On 16S Gene Sequence

The phylogenetic relationships of 74 species,44 genera,10 families of Pleuronectiformes, which comprised of 43 species,23 genera,7 families of flatfishes sequences determined in the study and 50 species,37 genera,10 families of flatfishes sequences downloaded from GenBank, were studied based on mitochondrial DNA 16s rRNA gene. Molecular phylogenetic trees were referenced to sequences of some Scorpaeniformes, Perciformes and Beryciformes species, and conducted by the methods of Neighbor Joining, Maximum parsimony and Bayesinain inference. The results were as following:(1) It was surprised that the putative out-group Scorpaeniformes, Perciformes and Beryciformes were tending to group within Pleuronectiformes. Different combination of out-group affected the cluster of familiy in Pleuronectiformes, but the monophyly of families and relationships among genera remained unchanged. The monophyly of Bothidae, Soleidae, Cynoglossidae, Samaridae, Poecilopsettidae and Citharidae were supported, except for Paralichthyidae. It was insufficient to settle the relationships above family level but well-resolved in the monophyly of families and relationships of genera when using mitocondrial DNA 16s rRNA gene as molecular marker in Pleuronectiformes.(2) Pleuronectidae was clearly composed of two clades, Pleuronichthys formed a clade alone, and the remained genera together formed another. Paralichthyidae was subdivided into three clades:Pseudorhombus-Tarphops, Paralichthys and Tephrinectes. It was noteworthy that Paralichthys was clustered with Pleuronectidae, indicating their close relationships. Tephrinectes formed a independent clade, its phylogenetic positon was isolated, hence the result supported the removal of T. sinensis from Paralichthyidae(Hoshino and Amaoka,1998), and suggested to elevate the genus Tephrinectes to the rank of family Tephrinectidae. In Sole idea, Aesopia was clustered within Zebrias, and they were morphologically similar also, so we suggested to abandon Aesopia and put A. Cornuta into Zebrias. In Cynoglossidae, C. purpureomaculatus and C. abbreviatus could not be differentiated, and C. lightiand C. Joyneri were also intentioned together.(3) Phylogenetic relationship of Pleuronectiformes did not necessarily linked with eye position whose roles in flatfish taxonomy need to be reassessed.