DNA Barcoding Of Common Scorpaeniformes Of China And Its Adjacent Areas

The Scorpaeniformes or mail-cheeked fish,one of the five largest ichthyological order in the world,is the important part of the global marine biodiversity and fishery resources.Recently,a phenomenon of resource recession during some mail-cheeked fish due to over fishing,marine environmental pollution and other human factor.Since similar morphological features among relative species,the traditional morphology method finds it difficult to give this group an accurate identification.Besides,some scorpaeniformes are ichthyoacanthotoxic,meaning an accidental touch may poison humans.Therefore,an accurate identification of these scorpaeniformes groups are the preconditions for solving the problems we mentioned above.DNA barcoding based on mitochondrial cytochrome c oxidase subunit I(COI)gene sequence has been developed into a successful tool in animal identification so far.Thus,based on the scorpaeniformes sampled from coastal waters of China together with homologous sequences downloaded from GenBank,a total of 534 specimens belonging to 118 species within 6 suborders,15 families,57 genuses were investigated in this study to explore the validity of DNA barcoding for identifying some common scorpaeniformes group and provide data to enrich the scorpaeniformes database of DNA barcode,and also give a reference for identify this group accurately and effectively.The findings are as follows:A total of 335 variable sites were found in the specimens,and about 64.78% of variable sites among the third position of the codons.All sequences after editing ranged in length from 552 to 652 nucleotides(mean: 621 bp).Based on 118 morphospecies,there were 116 clades on the NJ tree.Among which,105 species can cluster smoothly and form a monophyletic clade with unique species during 105 clades,while 13 species cluster disorderly within 11 clades.The mean genetic distance values of intra-clades and extra-clades were 0.41% and 22.28%,respectively,indicated that extra-clades genetic distance were approximately 54-fold higher than the intra-clades.The average genetic distance based on K2 P model were analyzed in each clade.The values within and between suborder were 12.67% and 23.30%,respectively.Similar values were obtain in family level,con-familial genetic distance at averaging11.35%,whereas between family at averaging 21.52%,and within and between genus were 4.01% and 20.02%,respectively.The genetic distance values were significantly different in the species taxonomic level,the values were 0.81%(from0% to 17.98%)and 9.94%(from 0.47% to 22.70%)for intraspecies and interspecies,respectively.Mean con-generic genetic distance were approximately 12-fold higher than the con-specific one.Except the species with only one specimen(33 species),about 96% of species with a low genetic distance which less than 2% threshold.Besides,genetic distance of more than 89% of species were less than 1%,and only 3species have intraspecific levels >2%,which indicated that the vast majority of common scorpaeniformes species meet the reference of 2% threshold.The result of automatic barcode gap discovery is similar to morphological identification,showed that there were 112 molecular group after analysis.Based on the results above,DNA barcoding can discriminate the majority(more than 88%)of Scorpaeniformes species in the present study,but maybe not suitable for higher taxonomic levels.The findings sustain the classification that 3 species Agaammus agrammus,H exagrammos otakii and H.octogrammus belong to the same genus Hexagrammos.At the same time,we consider that Chelidonichthys spinosus is synonyms of C.kumu.In view of the some results published in scientific jounals and the remarkable divergence in our reseach,cryptic species may exist in Platycephalus indicus from the South China Sea.Pterois lunulata have a closest relative with P.russelii as shown on NJ tree,P.lunulata may get evolve from P.russelii.Sebastes hubbsi and Sebastes longispinis cluster disorderly,perhaps reflecting introgressive hybridization between these two species or incomplete lineage sorting.Clustering disorderly in some species maybe influenced by some aspect,such as human factor,introgressive hybridization or recent evolutionary radiation,which need for further work and voucher specimen rechecks to study them systematically and thoroughly.