Molecular Phylogenic Study To Species Of Libellulidae (Odonata: Anisoptera) Based On COI Gene

Dragonflies are an ancient group of insects, and a key group in understanding the evolution of insects and insect flight. Superfamily and family distributions in Odonata reflect ancient vicariance events, and historical biogeography researchers often use dragonflies as their research objects. Members of Libellulidae are generally large, abundant, and conspicuous predators in many freshwater ecosystems and play an important role in structuring aquatic communities. In addition, this family displays remarkable diversity in behavior and morphology and consequently has been the focus of studies on genital morphology and sperm competition, sexual selection, comparative population ecology, phylogeography, and the evolution of mating behaviors. However, these studies are conduct without a clear phylogenetic relationship of the taxa. Thus, to reconstruct the phylogenetic relationship of this taxa seems very important and urgently. Hence, the study of morphology diversity, ecology, behavior, and distribution of Libellulidae species should be conducted with reference to a phylogenetic framework.Mitochondrial cytochrome oxidase subunit I (COI) gene is coding cytochrome oxidase subunit I. COI is a very important part of cytochrome oxidase. COI is a frequent using molecular marker on insect phylogenetic study. In the present study, we reconstructed the phylogenetic relationships of partial species of Libellulidae based on COI gene by using Neighbor-Joining (NJ), Maximum Parsimony (MP), Maximum Likelihood (ML) and Bayesian Inference (BI) methods. The conclusions are showed as follows:1, The average contents of A, T, C and G to COI gene of 14 species in Libellulidae are 31.5%, 36%, 15.8% and 16.7%, respectively. A+T content is 67.5%, while G+C content is 32.5%, which shows a strong A+T bias. These sequences code 234 amino acids and contain 19 kinds of amino acids, respectively. The contents of Leu and Val are very high and without Cys in the sequence.2, Ratio of transition to transversion(R) of COI gene sequence is 1.088 to the 14 species. Transitions(TS) are slightly higher than transversions(TV), most transitions occur between T and C, while most transversions occur between A and T. R value of first position of codon is 3.3, the third position has a high ratio of TS and TV, TS are 67.7% of sum total, and TV are 85.5% of sum total. The relationship between P distance and Ratio(R) is consistent with the typical distance-dependent character of mtDNA in Insecta, with the increase of p distance R value decrease. I use the trendline with the highest R square value. R square value of TS to p distance and TV to p distance is 0.7258 and 0.7011 respectively. The result of substitution saturation analysis shows that its substitutions are not saturated.3, Trees reconstructed using different method is not support each other. Phylogenetic relationships among genera are still not dear. Branch is in some sense chaos. Thus, I can not deduce relationship among genera. The reason is possible as follow. First, COI gene is not a suit molecular mark. Second, the number of species in the study is too small. COI gene has a higher bootstrap support to branch within genus. So I believe COI gene is an effective mark to deduce phylogenetic relationship within genus.4, Sympetrum uniforme and Crocothemis servilia always gather together and forming a branch with high bootstrap support.5, Results of my study are not support subfamily classification system by Wilson.