Genetic Diversity Of Ctenopharyngodon Idellus Populations From Three Major Watersheds Based On Mitochondrial Cytochrome B

The grass carp （Ctenopharyngodon idella）is a species of cyprinid fish native toEast Asia and is a kind of important economic fish in the world now. It widelydistributed all over China. In this study, the sequences of complete mitochondrialCytochrome b（MtDNA Cytb）were used to analyze the genetic diversity of160grasscarp from11different geographical groups in the Yangtze, the Pearl and the Amurriver. Results were as following:1、1123conservative sites and17variable sites（included10single variable sitesand7parsimony informative sites）were detected in the1140bp length of MtDNACytb. A total of18haplotypes is detected from160individuals, and6haplotypes areexisted two or more groups. There are8haplotypes in Nanyuepo of Hunan province,and5haplotypes in Hejiang of Sichuan and Eishui of Hubei province. According toNJ, ML, MP and UPGMA genealogical trees,18haplotypes did not from distinctpedigree structure, and each haplotype distributed dispersedly in differentpopulations.2、The total haplotype diversity (Hd) of160individuals is0.750±0.017whereasthe total nucleotide diversity (Pi) is0.00102±0.000733，demonstrateing a low level ofgenetic diversity among grass carp, and high haplotype diversity and low nucleotidediversity pattern. Compared with genetic diversity among the Yangtze, the Pearl andthe Amur river, the highest is the Pearl river （Hd=0.706±0.061，Pi=0.00104±0.000753）, the Yangtze river is second （Hd=0.704±0.033，Pi=0.00092±0.00068）, the Amur river is the lowest （Hd=0.425±0.099，Pi=0.00037±0.000396）.There exisits a high genetic divergence between the Pearl andthe Amur river acoording to differentiation index (Fst) and gene folw (Nm), and thereare a low genetic divergence between the Yangtze and the Amur river. There isundifferentiated among6groups in the Yangtze river,but differentiated among4groups in th Pearl river.3、The analysis of molecular variance, based on samples from three groups (theYangtze, the Pearl and the Amur river), showed that75.17%of the tatol geneticvariance was contributed by within populations variation, and17.90%contributed byamong groups variation. The genetic variance of grass carp is mainly come fromwithin populations. But p value of among groups variation（P=0.00293<0.05）is significant, suggesting that geographic isolation has an effect on genetic variance ofgrass carp. The distance between and within all groups is small(0.001~0.002), and didnot make difference subspecies.4、The results of neutrality test, analysis of mismatch distribution and TCSnetwork between haplotypes observed in grass carp were inferred grass carp’spopulation dynamic.160individuals in the Yangtze, the Pearl and the Amur river as awhole were analyzed, the neutrality test showed that Tajima’s D value, Fu’S Fs valueis negative and also significant, suggesting grass carp has a expansion of population inhistory. A unimodal distribution in the nucleotide mismatch distribution diagram and aradial TCS network diagram also came to the same conclision. The populationexpansion of grass carp population appeared in about22.8~11.4million years ago, inthe Middle and Late Pleistocene.