The Origin Of The Winged Insects Based On Complete Mitochondrial Genome

Ephemeroptera and Odonata belong to Insecta,the sub department of Palaeoptera,are the two groups of the most primitive winged insects,at present.But,their relationship remains unresolved,based on the morphological analysis or molecular data.Up to now,there are four hypotheses:Palaeoptera(Ephemeroptera+Odonata),Chiastomyaria(Ephemeroptera+Neoptera),Metapterygota(Odonata+Neoptera)and other(Ephemeroptera+Plecoptera).Plecoptera is an ancient insect group in Neoptera,its classification status in Neoptera has not been determined.Such as in parallel with Orthoptera,Dermaptera,or Embioptera,even independent of other Neopterans.Currently,molecular markers used in phylogenetic studies have nuclear genes,mitochondrial fragments and whole mitogenome,The mitogenome was recommended as the a effective molecular marker in phylogenetic study,for its maternal inheritance,and low rate recombination,and can solve the relationship in and above family level.This research determined 21 mitochondrial genome,from 8 families,15 genera of Ephemeroptera,4 families,4 genera of Odonata,2 families,2 genera of Plecoptera,discussing the phylogenetic relationship among and between these groups.For the further research on the effect of outgroup to phylogenetic analysis,via selecting the different outgroup to construct Bayesian phylogenetic tree(BI),discussing the stability of tree occurrence research system.The complete mitochondrial genome of Isonychia ignota,Vietnamella dabieshanensis,Serratella sp.,Epeorus sp.,Heptagenia sp.,Iron sp.,Leptophlebia sp.,Uracanthella sp.,Ephemerellidae sp.,Perlidae sp.and Nemoura sp.are 15105,16006,16751,15338,15352,15508,15534,15160,15154,15763,15735 and 15026 bp in length,respectively.The left are lack of some genes,their length is from 13698 to 15149 bp.For the gene arrangement,the heptageniidae sample(Epeorus sp.,Heptagenia sp.,Iron sp.,Cinygmina obliquistrita)all have an additional trnM gene,arrangement between trnl and trn Q;the trnI in all ephemerellidae sample(Uracanthella sp.,Serratella sp.,Drunella sp.,Ephemerellidae sp.)occur inversion phenomenon,even the trnI gene in Uracanthella sp.appeared a repeat after inversion,the trnl gene of Ephemerellidae sp.appeared 2 repeats after inversion;rest samples have the same gene arrangement with the ancestral insect.The rearrangement in heptageniidae fits tandem duplication random loss model,and gene rearrangement in ephemerellidae sample fits gene recombination and tandem duplication nonrandom loss model.For the base composition,all the genomes are obviously AT bias,and Odonata is slightly higher than other two;heavy chain has positive AT-Skew,except,the heavy chain of Ephemerellidae sp.,Drunella sp.,Uracanthella sp.,Rhoenanthus sp.,Potamanthus kwangsiensis,Leptophlebia sp.and Vietnamella dabieshanensis is negative AT-Skew,the above situation is indicative of the family of Ephemeroptera subjects have evolved different evolution.For the protein coding gene,all protein coding genes use the ATN or GTG as start codon,and the TAA,TAG℃ TA-or T--as the termination codon,the incomplete termination codon are highly appeared in nad5,nad4,Cytb,cox2,and cox3 genes.Atp6 gene is the most conserved gene of all protein coding genes,followed by atp8,cox3 and nad3 genes,while coxl,Cytb and nad5 have rather changes.For the region,the control area of these species are not very long,the longer control region always with several tandem repeats;except for control area,Drunella sp.,Uracanthella sp.and Serratella sp.have another large noncoding areas,it is speculated that these may be some residual after gene rearrangement.According to the BI phylogenetic tree:it is agree with Chiastomyaria;Plecoptera is the original species in Neoptera,and close to Dermaptera;Odonata,Ephemeroptera and Plecoptera are monophyletic.the relationship in Odonata is relatively clear,three suborders are monophyletic,Aanisozygoptera close to Anisoptera;the families involved in Odonata are monophyletic,in addition to coenagrionidae;the Pisciforma of Ephemeroptera relatively unusual,probably due to the long branch attraction of Baetidae;Siphlonurus immanis placed in ephemeridae,explain that ephemeridae is paraphyletic;overall,the systematic in Ephemeroptera is quite chaotic,thus,additional researches are needed.