The Study On Mitochondrial Genomics Of Cimbicidae

The Cimbicidae is a family of Symphyta,Hymenoptera which consists of four subfamilies,Cimbicinae,Abiinae,Corynidinae,and Pachylostictinae,mainly found throughout the Palaearctic Region,Oriental Region,Nearctic Region,and Neotropical Region(Corynidinae and Abiinae are found in the Palaearctic Region,Oriental Region,and Nearctic Region,Pachylostictinae is found only in Neotropical Region).At present,205 species of 22 genera of this family are known in the world,some of which belong to important forest pests.Cimbicidae is currently poorly studied based on molecular data,and it is difficult to discern the phylogenetic relationships of the Cimbicidae based on morphological data alone.Therefore,it is necessary to study the phylogenetic relationship of Cimbicidae based on the sequencing and analysis of the mitochondrial genome and to explore the origin and early evolution of Cimbicidae.In this study,we sequenced the mitochondrial genomes of 22 species in 14 genera of Cimbicidae,combined with three cimbicid mitochondrial genomes downloaded from NCBI for comparative analysis,including base composition,codon usage,gene rearrangements,selection pressure,and secondary structure comparison analysis,and the phylogenetic tree was constructed using maximum likelihood and Bayesian method.The main results are as follows:1.The 25 mitochondrial genes of Cimbicidae range in length from 14881 bp(Corynis lateralis)to 15941 bp(Palaeocimbex sp.).The whole mitochondrial genome of Cimbicidae is AT-biased overall(78.47～82.68%),with the AT bias skewed towards A and the GC bias skewed towards C.2.In addition to the common ATN start codon,two of the 13 protein-coding genes of Cimbicidae start with TTG(COX1 in Abia niui and ND4 in Zaraea mengmeng).The termination codon is dominated by TAA,but in ND5,both the Cimbicinae(except for Odontocimbex svenhedini and Pseudoclavellaria amerinae)and Corynidinae terminate with an incomplete-T,whereas Abiinae all terminate with a complete TAA,showing a strong phylogenetic signal.3.The topology of the phylogenetic tree constructed from 12 unsaturated protein-coding gene sequences was stable with 99% or above confidence in most branching nodes,and the same tree topology was produced using both ML and BI methods.The results showed that Cimbicidae is divided into three major clades(except for Pachylostictinae).In this study,the Cimbicinae was divided into four clades based on their phylogenetic relationships: Cimbicini,Odontocimbicini,Trichiosomini,and Leptocimbicini.4.Compared to ancestral species,gene rearrangements in Cimbicidae are more variable,with rearrangements occurring mainly between rrn S and COX1,involving25 cimbicid mitochondrial genes sharing eight gene arrangements(Abiinae,Corynidinae,Cimbicini + Odontocimbicini,Trichiosomini,and Leptocimbicini,respectively).The evolutionary history of the gene order of Cimbicidae was obtained by placing the gene rearrangements on a phylogenetic tree.5.The 25 cimbicid t RNA and r RNA genes were divided into five groups according to their phylogenetic relationships and labeled the different sites according to the corresponding classification units.It was found that some structures were more stable and showed the specificity of different orders,and some had greater base-pairing differences.6.To investigate the differences in selective pressure behind the five clades of Cimbicidae,the Two ratio branching model was used to calculate ω values for the five clades and it was found that within Cimbicidae(except for Pachylostictinae)the Corynidinae was subject to the strongest purifying selection and the species diversity was the lowest,while the Cimbicinae was subject to the weakest purifying selection and the species diversity was the highest.