Study On Mitochondrial Genome Analysis And Phylogenetic Relationship Of Insects In Three

Tetrigoidea is a superfamily of Caelifera in Orthoptera, and was regarded as a primitive taxa of Caelifera. There are about270genera and1500species known in this superfamily. Due to their small size and slight damage to crops, little concern and studies have focused on this group. However, in recent years, along with the growing recognition of their important status in phylogenetic and systemic research, studies about Tetrigoidea began to increase. But most of the studies were still only focused on morphology or single genes, few studies are on the mitochondrial genome scale. There are only2entire Tetrigoidea mitochondrial genomes in GenBank database.We determined almost the entire mitochondrial genomes of Formosatettix qinlingensis, Coptotettix longjiangensis and Thoradonta obtusilobata by PCR amplification and sequencing. The new mitochondrial genomes were annotated with reference to the mitochondrial genome informations of Tetrix japonica and Pedopodisma emiensis. Combining with other Caeliferan mitochondrial genomes in the database, protein-coding genes were completely compared, and phylogeny of Caelifera was reconstructed. By amplificating and sequencing partical sequences of16S rRNA, a phylogenetic relationship within Tetrigoidea was discussed combining with sequences in the database. The main conclusions drawn from this study were listed below:1. The obtained sequences length of Formosatettix qinlingensis, Coptotettix longjiangensis and Thoradonta obtusilobata mitochondrial genomes are15,180bp,14,495bp and14,538bp respectively.16S rRNA gene and13protein-coding genes can be annotated, but some of the tRNAs, part of12S rRNA gene and D-loop region were not sequenced through. All3new mitochondrial genomes have a high A+T content, the average A+T content is73.5%.2. All protein-coding genes of Caeliferan mitochondrial genomes in this study have an obvious AT skew, while the GC skew is weak. By comparing codons of mitochondrial PCGs with mitochondrial tRNA anti-codons, we found that not all codons with high frequency corresponding to mitochondrial tRNA anti-codons, which indicated that protein synthesis in mitochondria needs collaborations of tRNAs coding by nuclear and mitochondrial genomes. 3. The phylogeny of caelifera were reconstructed using MP, ML and BI method based on all13protein-coding genes. The monophyly of Acridoidea and Tetrigoidea were supported in the analysis. Scelimenidae was more primitive taxa compared to Tetrigidae. Genera Tetrix and Alulatettix may have a close relationship.4. According to the study of data partition and gene utility, different genes contributed uneven to the phylogenetic tree, both nucleotide and amino acid sequences of the ND series genes (ND1-6, ND4L) contributed most to the phylogenetic tree. However, when their contribution associated with length, an obvious positive correlation was found between them.5. The phylogenetic information statistics of different codons in protein-coding genes indicated that the3rd codon contains more informations than the1st and2nd codons, so the3rd codon should not be excluded when construct phylogenetic tree. According to the results of PartitionFinder software, there are great differences among different codons in protein-coding genes, so these sites should be partitioned into different parts in the phylogenetic analysis.6. Monophyly of genera Saussurella, Eucriotettix and Thoradonta were supported by MP, ML and BI trees based on partical sequences of16S rRNA gene, but the monophyly of Tetrix, Coptotettix and Euparatettix were not supported. Systolederus and Teredorus gathered into a clade in all trees, indicating their close relationship.