Molecular Phylogenetic Research On MtDNA Cytb Of Chrysomelidae

The Chrysomelidae belongs to Chrysomeloidea Coleoptera and is a very important group of economics insects. Most of them feed on plant's stalk and leaf, so as to do great harm to production and human being's lives and draw lots of attention for a very long time. With the development of the technique of experiment, the research on the insects of Chrysomelidae has proceeded extensively and deeply, and now it goes to the molecular level. Mitochondrial DNA (mtDNA) is a kind of maternal transmitted gene, which becomes an efficient symbol in the study of molecular phylogeny and the construction of phylogenetic trees, because of its conservation and convenience for experiments. Many kinds of mtDNAs have been used to study the insects of Chrysomelidae. By 23rd March 2004, there have been 883 records about mtDNA of Chrysomelidae in the data bank of NCBI, but the record of cytb is 0. cytb is the protein-coding gene and known most clearly in mtDNA. It's often used to study Diptera but never to study the phylogeny of Chrysomelidae.This article first used cytb as molecular symbol to study the molecular phylogeny of Chrysomelidae that filled the blank in this field. Total 18 cytb sequences were obtained that respectively belong to three subfamilies by means of PCR. 390 nucleotide sites were analyzed using Mega, Phylip and Crioceris duodecimpunctata were chosen as outgroup to build the phylogenetic tree. The conclusion were as follows:1 .The cytb gene sequences' content exists bias of A (32%) and T (40.9%), and the content of GC is 27.1%. The 4 sorts of nucleotide in three codon sites are not average, especially in the third site. The substitution rate in three different codon sites is not the same, the faster in the third site and the slowest in the second site.2.Transition represents the bias of T←→C, and transversion represents the bias of T←→A. The average p distance is 0.183. Transition and transversion have a good linear relation with genetic distance. The ratio of transition and transversion(R) is 0.84,and the ratio of Chrysomelinae(0.71) is lower than the average, so it is considered as the most ancient species in Chrysomelidae.3.Through building UPGMA, NJ, ME, MP> ML trees of gene and amino acid ,Ifound that the amino acid trees have better support for consistency and statistics, so it has more advantage to build phylogenetic tree .4.The relationship inside and between the categories was analyzed through the phylogenetic tree, which indicates that the relationships among Monolepta Chevrolat, Paleosepharia Laboissiere and Atrachya Dejean are very close. Alticinae formed in the middle of tertiary has more close relationship with Chrysomelinae came into being in the middle of Carboniferous than Galerucinae also formed in the middle of tertiary, so I draw a conclusion that the evolution rate of cytb gene of Chrysomelidae is not in accord with molecular clock. The rate of Alticinae is lower than that of Galerucinae.5.The research on phylogenetic tree shows that cytb gene is an efficient symble in the study of the phylogenetic evolution inside of genus, between of species and subfamily. Because of the classification based on cytb gene between of genus and inside of subfamily is ambiguous, the efficiency of the cytb gene as a molecular symbol is about to be discussed through further study.