Molecular Phylogenetic Analysis Of Polyrhachis (Hymenoptera: Formicidae: Myemicinae)

Polyrhachis belongs to Myemicinae, Formicidae, Hymenoptera. It is the second largest genus of Formicidae. 477 species have been described all over the world, and mainly distribute in Africa, Asia, Australia and Oceania. The molecular phylogenetic analysis of Polyrhachis has not been studied in China, and there is a wide gap with the advanced level of other counties. So, the research in this area will provide basis for establishing the right Formicidae phylogenetic relationship, the effective protection, using and prevention of ants. And the study has important significance in accumulating the phylogenetic tree and the gene bank of ants, also establishing the status of a similar study in our country. The Cytb, COI and COII gene sequences of 10 species of Polyrhachis were amplified by Touchdown PCR in this study, and the sequences were aligned by software ClustalX1.83. Then I analyzed their nucleotide composition, amino acid composition, codon usage, nucleotide substitutions and p-distance by MEGA4. And I reconstructed the phylogenetic relationships of these species with neighbor-joining (NJ), maximum parsimony (MP) and Bayesian inference (BI) methods, using 3 species of Camponotus as outgroups. The conclusions are showed as follows:1. The high A+T contents of Cytb gene of 9 species, COI, COII and COI+COII genes of 5 species are 71.2%, 75.9%, 75.0% and 75.2% respectively, which shows a strong A+T bias. The 465bp fragments of Cytb gene code 155 amino acids and contain 19 kinds of amino acids. The 174bp fragments of COI gene code 58 amino acids and contain 17 kinds of amino acids. The 552bp fragments of COII gene code 184 amino acids and contain 20 kinds of amino acids. The 726bp fragments of COI+COII gene code 242 amino acids and contain 20 kinds of amino acids. And there is a strong bias in amino acids contents.2. These analysis of nucleotide substitutions based on Cytb, COI, COII and COI +COII gene sequences show that transitions are slightly higher than transversions, and transitions mostly occur between T and C, while transversions mostly occur between T and A. Substitution of the second position of codons are the lowest but the third position are the highest.3. These analysis of p-distance which has not been adjusted based on Cytb gene, COI, COII, the COI+COII gene show that, their homology are very high, and the ranges are 0.815~0.918, 0.862~0.943, 0.855~0.962 and 0.857~0.957 respectively.4. The relationship between p-distance and ratio of transition to transversion (R) based on Cytb, COI, COII and COI+COII gene sequences are consistent with the typical distance-dependent character of mtDNA insect, with the increase of p-distance R value decrease. The results of substitution saturation analysis based on transition(Ts) to p-distance and transversion(Tv) to p-distance relationship show that their substitution are not saturated. All data have contained strong phylogenetic signals.5. The reliable phylogenetic relationship of 10 species of Polyrhachis is {[(Polyrhachis subpilosa + P. illaudata)+ P. vigilans + P. proxima]+ P. rastellata + P. lamellidens +(P. moesta + P. bicolor + P. dives)+ P. halidayi}. However, the phylogenetic relationship among P. rastellata, P. lamellidens and P. halidayi still need to discuss.