The Complete Mitochondrial Genomes Of Four Neuropterodea Species And Their Phylogenetic Significance

Neuropterodea is one of the most primitive groups of holometabolous insects,including the orders of Megaloptera, Neuroptera and Raphidioptera.They containmore than6300extant knownspecies all over the world, with the their number ofactual species being estimated up to10,000. The fossil records of Neuropterodeaare extremely rich in the Mesozoic, however, their extant species are relatively lessthan the extant species, which are mutually isolated in biogeographicdistribution.Accordingly, it is generally considered that such groups hasexperienced its heyday and the vast majority of their groups become extinct duringtheir evolutionary history. So far, many problems about their origin and evolutionare still standing as unsolved issues, with the relevant results being far away fromconsensus in respect of morphological, molecular and palaeontological evidences.In order to further explore the evolutionary patterns (the evolutionary pathdiagram and timescale) of the main holometabolous insect groups, especially of themain Neuropterodea lineages, the complete mitochondrial genomes of the fourrepresentative Neuropterodea species(Neochauliodes rotundatus, Neochauliodesfraternus, Ascalohybris subjacens and Epacanthaclisis banksi) were sequencedusing PCR and primer walking technologies. Meanwhile the gene organization andvariability of their mitogenomes were analyzed with detail, combined with thecorresponding sequence data of other available holometabolous insect groups.Additionally, the phylogenetic relationship and the divergence time analyses aboutthe main Neuropterodea lineages were conducted based on their calibrated fossilsrecords using multidisplinary methods of molecular phylogenetics and molecularclock dating, in order to provide new and valuable informations for theNeuropterodea evolutionary studies.The results showed that the complete mitochondrial genomes of the fourrepresentative species of Neuropterodea,N. rotundatus, N. fraternus, A. subjacensand E. banksiare15774bp,15768bp,15873bp and15870bpin length, respectively, and each of them containing13protein-coding genes(ATP6,ATP8,COI-III, ND1-6, ND4L, Cytb),2ribosomal RNA genes (lrRNA and srRNA),22transfer RNA genesand a A+T-rich region (putative control region, D-loop);however, the tRNA arrangement patternof Neuroptera istRNACys–tRNATrp–tRNATyr(CWY),ratherthan that of the other Neuropterodea insects(Megaloptera, Raphidioptera): tRNATrp–tRNACys–tRNATyr(WCY); the remaininggenes are arranged in the same order and orientation as that of the hypotheticalancestral insect mitogenomes with no gene rearrangement or gene deletion; all theprotein coding genes (PCGs) use standard initiation codons ATN, excluding fewgenes being started with TTG、CTT and TTA; all the PCGs use common stop codon(TAA or TAG) with the exception of a few genes being terminatedwith a single Tor incomplete codon TA; a number of intergenic spacer sequences and overlappingsequences are interspersed throughout the whole mitgenomes, with the intergenicspacer sequences and overlapping sequences numbered from7to13and8to12,totaling of33bpto236bp, and22bpto40bp, respectively, and among thesenoncoding regions, the ATP8andATP6is overlappedby7bases(ATGATAA), whichis characteristic of Neuropterodea; the non-coding A+T-rich regioncontains somerepeated motifs of single nucleotides, such as (A)2-11,(T)2-11,(G)2-3,(C)2-6, aswell asa lot of microsatellite-like elements, such aspoly(A), poly(T),(TA)n and(AT)n.The phylogenetic trees of the main holometabolous lineages werereconstructed using the bayesian inference (BI) and the maximum likelihood (ML)methods. The results showed that the topological structure of the reconstructedtrees is:((((((((Megaloptera+Neuroptera)+(Mecoptera+Diptera))+Coleoptera)+Lepidoptera)+Siphonaptera)+Raphidioptera)+Trichoptera)+Hymenoptera)+Strepsiptera. It is obvious that the Neuropterodea is a paraphyletic group: theMegaloptera and the Neuroptera make up a monophyletic group, with one beingsister to the other; the Raphidioptera is an independent clade. The results of thephylochronological analysis showed that the divergence of the holometabolaoccurred during the early Carboniferous (estimated mean:332.7Ma,0.95confidence interval:298-350Ma), the Megaloptera, Neuroptera, Raphidiopteraoccurred during the late Triassic about223.6Ma (205.1-242.1Ma,95%IC), 208.9Ma (185.1-232.7Ma,95%IC),223.9Ma (205.4-242.4Ma,95%IC), rspectively.