Phylogenetic Analysis Of The Family Loliginidae Based On Complete Mitochondrial Sequences

We characterized and compared these genomes among nine species,six newly sequenced,including Uroteuthis chinensis,Loliolus japonica,Loliolus uyii,Uroteuthis duvauceli,Doryteuthis opalescens and Loliolus Beka.In the end,16S control regions and whole genomes were used to construct phylogenetic trees by ML method to analyze the phylogenetic relationships of 9 species of Loliginidae,providing molecular level evidence for the classification and evolution of Loliginidae.The main results were summarized as follows:1.The mitochondrial genomes of the nine analyzed loliginid species range in size from 16631 to 17485 bp.Six species share the canonical mitochondrial gene content and arrangement,containing 37 genes encoding 13 proteins,22 tRNAs,and 2 rRNAs.The two ribosomal RNA genes,16S rRNA is located between the tRNAIle and tRNAVal genes,and 12S rRNA is located between the tRNAVal and tRNATrp genes.2.There are intergenic regions and overlaps between the six species of Loliginidae,The complete length of intergenic regions is between 1-410 bp,and the complete length of overlap regions is between 1 and 29 bp.The mitogenome base composition,A content is 40%,T content is between 31-32,C content is between 18-19%,G content is between 7-11%,and A+T content is Between 71-72%,there was a clear AT bias that was consistent with the characteristics of other species of Loliginidae.The cumulative lengths of the protein-coding genes across the species range from 11193 to 11223 bp,this accounts for 65.326 to 65.208%of the mitochondrial genome total length.13 protein-coding genes can be classified into two categories:COX3,ND2,COX1,COX2,ATP8,ATP6,ND4,and ND3 were encoded on the light strand,the rest including ND1,ND5,ND4L,CYTB,and ND6 were encoded by the heavy strand.Seven protein-coding genes(COX3,ND3,ND2,COX1,COX2,ATP8,ATP6)start with an ATG initiation codon;five protein-coding genes(CYTB,ND1,ND5,ND4L,and ND6)start with a CAT initiation codon,while ND4 uses TAT as the initiation codon.Six protein-coding genes(COX3,ND2,COX1,COX2,ND3,and ATP6)use TAA as the termination codon;four protein-coding genes(Cytb,ND6,ND1,ND5)use TTA as the termination codon,while ND4 and ND4L share the termination codon CTA;ATP8 uses TAG as the termination codon.There is overlap between some of the genes.For example,NAD2 and COI overlap by 29 nucleotides;ND4L and ND4 overlap by seven nucleotides;tRNAHis and tRNALeu overlap by three nucleotides.As for S.lessoniana,the gene arrangement and organization of the mitochondrial genome are totally different from the other eight specie.3.The non-coding regions in the loliginid species mtDNA include three almost identical non-coding regions.The length is 1409bp to 1570bp,and the similarity is 66.62%.4.The results showed that the branch classification of the six species of squid in this study was consistent with the traditional morphological classification,while the results of other scholars were divided.In the evolutionary tree,the Uroteuthis chinensis and the Uroteuthis edulis gathered together,the Loliolus japonica and the Loliolus uyii Loliolus beka gathered together.The classification of the Uroteuthis edulis and the Sepioteuthis lessoniana was confusing.We conjecture that there may be an unknown genus or subgenus within the Loliginidae.This work is the first report about the complete mitochondrial genomes of species in family Loliginidae.All these data have enriched the NCBI GenBank genome database.Also,the whole mitochondrial genomes were used to analyze the phylogenetic relationships of Loliginidae in this study.Our results will lay a good foundation for the further research of higher-order phylogenetic studies of Cephalopoda.