Molecular Evolution And Phylogenetic Study Of Mex1and Ras64B Genes In Melanogaster Species Group

Drosophila melanogaster species group subjects to Diptera Drosophilidae Genus Drosophila, Subgenus Sophophora, and it is the largest species group of Drosophilidae, including more than180species, most of which have been classified into12subgroups based on morphological characteristics. So far, several researches about the phylogeny relationships of the melanogaster species group have been done based on morphology, biogeography and molecular biology characteristics. However, because of the lack of information, the phylogenetic relationships among the species group remains controversial.In this study, the sequences of the mexl gene of23species and the Ras64B gene of24species within the melanogaster species group were directly measured for analysis of the phylogenetic relationships among the melanogaster species group. The analysis of molecular evolution with the two gene reveals that the coding regions of them are conserved. The evidences from the ratios of Ks/Ka and GCIII contents show that the coding regions undergo near-neutral selection. The exons of the two gene are conserved. There is no obvious insertion or loss for the introns, but the length of them among the species are different, which shows that the evolutionary rate of intron is faster than that of exon.In the study Drosophila pseudoobscura is selected as the outgroup, and phylogenetic trees are reconstructed based on the sequence data of mexl gene and the Ras64B gene with Neighbour-joining (NJ), Maximum likelihood (ML) and Bayesian method. Supporting values are calculated by bootstrap method. The result shows that the melanogaster species group are clustered into two main lineages:one lineage contains ananassae subgroup and montium subgroup; the other includes melangaster-suzukii-elegans-ficusphila-eugracilis-takahashii. For the melangaster subgroup and the east Asia subgroup, the phylogenetic relationships remains defferences, acrroding to the AU test, the result is that the Bayesian method is more credible. Additionally, in the melangaster complex species the phylogeny of D.simulansand D.sechellia are the most closely related species, but there remains controversial for the phylogenetic relationships about melanogaster species and simulans species.