Study On Population Genetics Of Caenorhabditis Sp.5

The Caenorhabditis is a free-living soil nematodes. Their life cycle is short, and easy to train laboratory. Since the genome sequences of C. elegans and its sister species C. briggsae have been completed, this group of worms have becomed not only the best modal organisms for developmental biology, neurobiology, apoptosis, but also for functional genomics research, and it is the best experimental subject for comparative genomics and evolution research. According to the current literature, there are more than 20 species of Caenorhabditis wild resources, C. elegans, C. briggsae, C. brenneri and C. remanei are widely distributed species in the world, like Europe, Americas and Asia. C.sp.5 was only discovered was only discovered in Asia (in China and Vietnam). The beginning reaserch of the Caenorhabditis is later in our country, and it is limited to the studies of neurology, toxicology studies in a very small number of laboratorys. The senven conservative sites in X chromosome of 18 strains of C.sp.5 were studied by WANG, but the population genetic diversity is not involved. In order to learn more about the the genetic structure and evolution laws of C.sp.5, we collected 948 samples in China from 2008 to 2010. They were separated and identified, and the studies of population genetic studies of them were carried out, and the following results were obtained:1. Nematodes were isolated from samples on the NGM plates, after pure culturing, nematodes were identified with the methods of morphology and molecular biology. The primers of 18S rDNA were used to PCR, after sequenced, the sequences were blasted in the database of NCBI.41 strains of C.sp.5 were identified. The evolutionary relationship of the 41 strains and all relational strains from the GenBank were systematically analyzed by 18S rDNA sequence analysis, molecular phylogenetic trees were constructed by using Neighbor-Joining and Maximum Parsimony. The results showed that all proposed strains of C.sp.5 had a closest relationship to JU727 and clustered into a branch at a significant confidence level. We analyze the Nucleotide composition of 18S rDNA sequence of all, the content of (A+T) is 56%, (G+C) is 44%.2. We amplified the mitochondrial COⅡgene sequences of 41 strains of C.sp.5. The effective sequences are all 696bp. The content of (A+T) is 74.4%, (G+C) is 25.6%, the bases are puite partial abnormal,31 haplotypes were defined by using the software DnaSP, haplotype diversity is 0.979(±0.008), nucleotide diversity (Pi) are 0.0123-0.179, average number of nucleotide differences (K) are 13.4. The evolutionary relationship of the 31 haplotypes of COⅡgene were systematically analyzed, molecular phylogenetic trees were constructed by using Neighbor-Joining (NJ) and Maximum Parsimony (MP). Among the 3 geographical populations, individuals from Hubei and Sichuan have a closer relationship relatively. Overall, the 31 haplotypes of COⅡgene sequences of C.sp.5 distributed in the phylogenetic tree irregularly.3,We selected 10 pairs of primers,10 conserved genes in X chromosome of 41 strains of C.sp.5 were amplified and sequenced, the length are 430-781bp, the total length of 10 conserved locus is 6763bp. The content of (A+T) is 49.9%, (G+C) is 50.1%. By using the DnaSP4.0, we obtained the results that the haplotype diversity of 10 sequences of the nuclear gene locus are 0.943-0.996, the nucleotide diversity (Pi) of that are 0.0123-0.179; The haplotype diversity of the total nuclear gene was 0.979 (±0.008), nucleotide diversity (Pi) of that is 0.0140.4. The neutral test was carried out to the C.sp.5 group based on the haplotypes of COⅡgene sequences,10 conserved nuclear gene sequences and total nuclear gene sequences of 41 strains of C.sp.5. The results show that these genes are strictly follow the null hypothesis in the DNA molecular level. In other words, the population of C.sp.5 in our reaserch are consistent with neutral evolution theory. In addition, We conducted dynamic analysis of population history based on the haplotypes of COⅡgene sequences and total nuclear gene sequences of 41 strains of C.sp.5, we found that the distribution of nucleotide mismatch of COⅡgene sequences and nuclear gene haplotypes showing multiple peaks. It suggests that the gene flow of this population is very frequent, the geographical isolation or rapid expansion did not exist, during the process of evolution the bottleneck effect of population did not exist yet.