Molecular Phylogenetic Analysis Of Acridoidea Based On COⅠ、cOⅡ And COⅢ Gene Sequences

Grasshoppers are general call of Acidoidea insects, which belongs Caelifera, Orthoptera,Insccta, with more than12000species known in the world and1200species recorded inChina. Most of which are pests in animal-breeding and agriculture, but some variants havesignificant economic values. Although phylogeny of the group has been investigated from avariety perspectives and at different taxonomic levels, phylogenetic relationships withinAcidoidea remain unresolved. In order to provide enough proofs for improving the taxonomicsystem, it is necessary to study the phylogeny of Acidoidea based on molecular markers.In this dissertation, the phylogenetic relationships of Acridoidea were analyzed based onmtDNA COⅠ, CO Ⅱ and CO Ⅲ genesequences. The complete sequences of the three genesof10grasshoppers were determined. Nucleotides composition and variation, amino acidcomposition, base substitution and substitution saturation were analyzed with MEGA, and themolecular phylogenetic trees were reconstructed by the microsoft MEGA and PAUP based onthe combined sequence of the three mtDNA genes and its amino acid sequence. The outgroupsequences and the data of22other grasshoppers were download from GenBank. Theconclusions are as follows:1. Nucleotides composition and variation: The gene of CO Ⅰi s moreconservative thanCO Ⅱ and CO Ⅲ. In the three genes, the second codon sites are the mostconservativepositions, and the third sites are the most variable positions. Average A+T content is68.5%-70.6%, and A+T content of COⅠ gene at thethird codon position is86.2%, whichshows a strong bias.2. Nucleotide substitutions: there is a higher rate of base substitution in CO Ⅰ, COⅡ andCOⅢ genes. The number of transitions and transvertions is equal approximately, the averageratio R is1, and all ratios R of the three coden sites are far greater than the critical value (0.4).The transitions in the3genes tend to saturation, but the transversions are not saturated.3. Coden and amino acid composition: There are503codens in CO Ⅰ gene,226in COⅡand261in CO Ⅲ. We inferred that theinitiator codon of COⅠis ATGA(GTGA, ATGG) bysequences Alignment. The initiator codon of CO Ⅱ and COⅢ is ATG, the terminator codon ofthe three genes are TAA or only T. Twenty Amino acids are encoded by CO Ⅰ, COⅡ andCOⅢ, respectively. The frequency of utilization of every amino acid isunbalanced. Leu, Ileand Ser are the most, Cys and Glu are the least. 4. Molecular Phylogenetic Analysis: Phylogeny trees were reconstructed by Neighbor Joining(NJ) and Maximum-parsimony (MP) using combined date of CO Ⅰ,CO Ⅱ and COⅢsequence. All trees shows an similar topological structure that outgroups are well separatedfrom the roots of all trees. The Acridoidea is a monophyletic group. In the8families ofAcridoidea, Oedipodidae, Chrotogonidae, Pyrgomorphidae and Pamphagidae aremonophyletic groups. Oedipodidae is the most evolved group, and then is Acrididae,Arcypteridae and Gomphoceridae orderly, Arcypteridae has a close relationship withGomphoceridae. Catantopidae is located in the central of the phylogenetic trees, andPamphagidae is more primordial than Catantopidae. Pyrgomorphidae and Chrotogonidae arethe most ancestral groups which keep a closer phylogenetic relationship. In conclusion, wespeculate the phylogenetic relationships of Acridoidea were:(Pyrgomorphidae+Chrotogonidae)→Pamphagidae→Catantopidae→(Arcypteridae+Gomphoceridae)→Acrididae→Oedipodidae.5. Based on the analysis of nucleotide substitutions, substitution saturation and molecularphylogenetic relationships, we affirmed that the combined sequences of CO Ⅰ, CO ⅡandCOⅢ were available in restructuring the phylogenetic relationships of Acridoidea. The threegenes are effective molecular markers on molecular phylogenetic analysis.