System Analysis Of Commom Cheletids (Acari: Cheyletidae) Based On Mitochondrial COâ…  And 12SrRNA Gene

This dissertation deals with the phylogenetic relationships among 5 species of 3 genera of cheyletids (Cheyletus malaccensis, Cheyletus fortis, Cheyletus aversor, Cheletomorpha lepidopterorum and Eucheyletia sinensis) by using the mitochondrial COâ… gene and 12S rRNA gene. The main contents and results are as follows: 1 Systems analysis based on COâ… gene of five species of cheyletidsThe research of five species of cheyletids present obvious bias in base composition, A+T content is significantly higher than that of G+C. This phenomenon is also common in other invertebrates mitochondrial DNA sequences.The COâ… gene sequence of five species of cheyletids shows that:There are no insertion/deletion/ termination codons in nucleotide sites.348 variable sites and 179 parsimony informative sites are detected.Preliminary study of Cheyletus malaccensis genetic relationship with its related species by using mtDNA-COâ… molecular level shows that: Cheyletus malaccensis and Cheyletus fortis has very close relationship. The genetic distance is between 0-0.039, within the genetic distance between 9 different populations of Cheyletus malaccensis. Analyze from the variable sites, COâ… gene sequences of Cheyletus malaccensis and Cheyletus fortis has very small differences,44 variable sites totally, increased by only 8 new variable sites. Judged from phylogenetic tree,5 populations of Cheyletus fortis is not a separate branch but included in 9 populations of Cheyletus malaccensis. These 2 species of Cheyletus collected from the same region gather together first, then different geographical populations gather together and last they gather with Cheyletus aversor. So it proves that:the differences between Cheyletus fortis and Cheyletus malaccensis were intraspecific level.Based on the determination and analysis of the mitochondrial DNA COâ… gene sequence, molecular phylogenetic tree of five species of cheyletids (Including 3 species of Cheyletus,1 specie of Cheletomorpha and 1 specie of Eucheyletia) is constructed. NJ and MP trees showed the same topology, so the phylogenetic relationships among these genus are (Cheyletus+Cheletomorpha)+Eucheyletia; The phylogenetic relationships among these 5 species of cheyletids are{[(Cheyletus malaccensis + Cheyletus fortis) + Cheyletus carnifex] + Cheletomorpha lepidopterorum} + Eucheyletia sinensis. 2 Systems analysis based on 12S rRNA gene of five species of cheyletids12S rRNA gene sequences of 5 species of cheyletids were determined and analyzed. Amplified fragments present obvious bias in base composition, A+T content is significantly higher than that of G+C. This phenomenon is also prevalent in other acari.6 different geographic populations of Cheyletus malaccensis have only one base difference in the gene sequences, while 2 species of Cheyletus carnifex have no. Genetic differentiation is very small. Different species in the same genus (genetic distance between 0-0.047) and different genera (genetic distance between 0.074-0.118) have some polarization, and it receives high degree of confidence. It evidenced that 12S rRNA gene sequence is suitable as the molecular marker of phylogenetic study between species and genera of cheyletids, but not suitable as the molecular marker of genetic differentiation within the same specie.Based on the molecular level of 12S rRNA gene, preliminary study of genetic relationships between 5 species of cheyletids demonstrated that:Cheyletus malaccensis and Cheyletus fortis has very close relationship.2 species of cheyletids in the same populations has the same sequences. But viewed from phylogenetic tree, Cheyletus malaccensis can be easy distinguished from other three species of cheyletids. So it also proves that: the differences between Cheyletus fortis and Cheyletus malaccensis were intraspecific level.From the NJ, MP phylogenetic tree shows that,3 species of Cheyletus gather together first, then gather with Cheletomorpha lepidopterorum of Cheletomorpha and last they gather with Eucheyletia sinensis of Eucheyletia. Phylogenetic tree based on the 12S rRNA gene shows the relationships between 3 genus are(Cheyletus + Cheletomorpha) + Eucheyletia.