Comparative Mitochondrial Genomics And Phylogeny Of The Aculeata In The Hymenoptera

The Aculeata(Hymenoptera: Apocrita)is one of the most speciose groups,comprising of the common eusocial wasps,ants and bees,including eight superfamilies(Chrysidoidea,Formicoidea,Pompiloidea,Scolioidea,Tiphioidea,Thynnoidea,VespoideaandApoidea).Current study supported the monophyly of the Aculeata,while the relationships among the major lineages of Aculeata remain unresolved.The mitochondrial genomes werewidely used in evolutionary and phylogenetic studies,however,most representative species in Aculeata have not been sequenced to date,which limited the study of comparative genomics and phylogeny in Aculeate based on mitochondrial genomes.This study sequenced the mitochondrial genomes of Aculeata and performed analysis with other published mitochondrial genomes.Undering the methods of comparative genomics,we analyzed gene content,intergenic region,codonusage,gene arrangementand tRNA secondary structures and explored the mechanisms of gene arrangement in the mitochondrial genomes of Aculeata.Finally,we reconstruced the phylogenetic tree of Aculeata.The main points were concluded as follows:(1)Twenty-six mitochondrial genomes representing 10 families from 5 superfamilies of Aculeata were determined by using high-throughput sequencing.The mitochondrial genomes of Pompilidae,Embolemidae,Dryinidae,Scoliidae,TiphiidaeandMutillidae were reported for the first time.Except for thetrn RinStilbum calens,nad6 inAnteon sp.,nad1,trnL1,trnV,trn C,rrnL,rrnSinMutillidae sp.1,trn I,rrnSinMutillidaesp.3,trnKinCampsomeris prismaticaandtrn QinPararrhynchium sp.and most A+T-rich regions,most all of the 13 protein-coding genes,22 tRN As and 2 rRNA genes were sequenced in the study in all species.(2)General features of the mitochondrial genomes in the Apoidea were compared.Among 41 mitochondrial genomes anlysised in this study,Colletes glgasand Leptomyrmex pallenshad the highest and lowest A+T content,respectively.The sign ofAT skew and GC skew were calculated for the whole genome and all protein-coding genes.AT-skews were positive in all species,while GC-skews were negative in most species.All of the protein-coding genes start with the conventional initiation codons(ATN).Most genes use ATT as start condon,while only 6 genes started with ATC.Most protein-coding genes used TAA as the stop codon,while 23 genes used incomplete stop codon TA,52 genes used T,and 20 genes ended with TAG.The length of overlapping regions among all genes was 1-10 bp,while there were large differences in the length range of the intergenic regions.Leu,Ile and Phe were the most frequently used animo acid,while TTA(Leu),ATT(Ile)and TTT(Phe)were the most frequenfly used codons in Aculeata mitochondrial genomes.Most tRNA genes of all species folded into a canonical clover-leaf structure with the dihydrouridine arm formed a simple loop,however,mosttrnS1 lost D-stem pairings in the DHU arm.We analysed the mitochondrial genomes evolution in Aculeata by calculating the values of nucleotide diversity(Pi),ratio of the rate ofnon-synonymous substitutions to the rate of synonymous substitutions(Ka/Ks)All Ka/Ks ratio were greater than 1.For individual protein-coding genes in holometabolousmitochondrial genomes,atp8 and nad2 evolved in the fastest rate.(3)Frequent gene rearrangementsoccurred in Aculeata mitochondrial genomes.Not only the t RNAs rearranged in all species,but also some protein-coding or r RNA genes were rearranged.Rearrangements of protein-coding geneswere found in Chrysididae,Bethylidae and Scoliidae.Gene rearrangement events mainly occurred in three hot spots: A+T-rich region-nad2,nad2-coxl and nad3-nad5.The remote inversion wasfound to be the mostmost frequent events.(4)The phylogeny of the Aculeata is reconstructed based on nucleotide sequences of protein-coding genes,the nucleotide sequences of protein-coding genes and RNA genes and amino acid sequences of protein-coding genes.All the results supported the monophyly of Formicoidea,Vespoidea,Scolioidea,Tiphioidea,and Apoidea.Vespoidea is identified as the sister lineage of Formicoidea.However,Chrysididae and Dryinidae of Chrysidoidea were not in one clade.All the phylogenetic tree indicated that Dryinidae sistered to all other species of Aculeata,except for the tree based on amino acid of protein-coding genes.Long-branch attraction may occurred in Mutillidae and Bethylidae,contributed to the paraphylyof Pompiloidea,Mutillidae sistered to Bethylidae,and grouped with Vespoidea and Formicoidea.When the species involved in Long-branch attractionwere removed,all the phylogenetic treesshowed that Chrysidoidea,Scolioidea,and Pompiloidea were classified into a group,while Vespoidea,Formicoidea and Tiphioidea were classified into another clade.