Genetic Diversity Of Chinese Sucker (Myxocyprinus Asiaticus) And Molecular Systematics Of Catostomidae Fishes

The family Catostomidae has 14 genera and about 80 species all over the world, mainly in North America. The Chinese sucker, Myxocyprinus asiaticus, is an endemic freshwater fish in China and the only representative of family Catostomidae in Asia. The fish is naturally distributed mainly in the Yangtze River, especially in the upper reaches. The wild fish source was greatly damaged due to over-harvesting and other human activities, to date the Chinese sucker has been an endangered species and has been listed in the second class of preserved animals in China. About this precious fish species, we have performed research work on 3 aspects. Firstly, on genome DNA and mitochondrial DNA levels, we detected the genetic diversity and population differentiation among 4 Chinese sucker geographical populations (Yibin, Wanzhou, Yichang, and Wuhan) from the Yangtze River based on RFLP, RAPD, SSR and DNA sequencing analyses. Secondly, we sequenced the 18S-ITS1-5.8S partial sequences from nuclear DNA and cytochrome b partial sequences from mitochondrial DNA respectively. By using these two markers, we performed molecular systematics research on Catostomidae fishes and compared the molecular variation model between Chinese sucker and other representative Catostomids. Thirdly, we studied the biogeography of Catostomidae fishes based on the molecular, fossil, and biogeographical evidences, especially about the biogeographical history of the Chinese sucker.It is necessary to learn the genetic background of the Chinese sucker in the Yangtze River in order to preserve and restore this endangered fish. We are the first research group to do this work using molecular methods. The RAPD and PCR-RFLP methods were used to detect genetic structure of Chinese sucker populations from the middle reaches of Yangtze River: Yichang section and Wuhan section. We screened about 80 RAPD primers, and only 3 primer produced polymorphism. The genetic similarity within the Yichang and the Wuhan population is 0.9274, 0.9313 respectively. The geneticsimilarity between them is about 0.9000. In PCR-RFLP analysis, 4uL aliquots of the PCR products of mitochondrial NADH dehydrogenase (ND-5/6) genes were digested by 12 restriction enzymes. Of 12 restriction enzymes types, 11 are monomorphic except Ncil enzyme. Only two kinds of haplotypes were found. The nucleotide diversity was 0.004, and the pair-wise sequence divergence was about 0.235%, which suggested that the genetic diversity of Chinese sucker was low. Seen from the electrophorisis patterns in the PCR-RFLP and RAPD analysis, we found that the genetic differentiation was formed between the two populations to some extent. Genetic diversity and population structure of the Chinese sucker was also assessed by sequencing the mtCR (mitochondrial control region) in 4 natural populations from the Yibin, the Wanzhou, the Yichang, and the Wuhan section of the Yangtze River. We obtained the mtCR sequences of about 920 base pairs. The average base composition was similar to other fishes that the average A and T contents were much higher than the average G and C contents (21.55C: 28.94T: 32.09A: 17.42G) . A total of 223 nucleotide positions were polymorphism, and these defined 39 haplotypes. Of the 39 haplotypes, 37(90%) are private and multi-sharing of haplotypes was seldom observed among populations. The average haplotype diversity (0.958) and the average nucleotide diversity (0.052) indicated higher level of genetic diversity of Chinese sucker globally. Analysis of molecular variation (AMOVA) of data revealed significant partitioning of variance (P<0.001) that most variation was from among populations (60.29%), and less from within populations (39.71%). The dendrogram or phylogenetic trees by the NJ (neighbor joining) and MP (maximum parsimorny) methods showed mosaic composition of the 39 haplotypes, suggesting that the populations were not significantly divergent. Nevertheless, we still recognized two divergence phylogenetic clusters: haplotype 34, 35, 36, and 39 consisted of the cluster B and the...