Studies On Genetic Diversity Of Loach (Misgurnus Anguillicaudatus) Populations From The Yangtze River Basin

Mitochondrial DNA cytochrome oxidase subunit I sequencing was used to investigate genetic diversity and genetic structure of eleven loach (Misgurnus anguillicaudatus) populations from Yangtze River Basin-Jiajiang population in Sichuan Province (SC), Chongqing population (CQ), diploid population in Wuhan city in Hubei Province (WHD), tetraploid population in Wuhan city in Hubei Province (WHT), diploid population in Dongting Lake (DTD), tetraploid population in Dongting Lake (DTT), Anqing population in Anhui Province (AQ), Poyanghu Lake population (PYH), Taihu Lake population (TH), Nanjing population in Jiangsu Province (NJ), and one population from the Huai River basion-Lianyungang population in Jiangsu Province (LYG). SRAP (Sequence-Related Amplified Polymorphism) markers and mitochondrial DNA control region sequencing were used to investigate genetic structure of four loach (Misgurnus anguillicaudatus) populations from two sympatric distribution areas of natural diploid and tetraploid loach-Dongting Lake (DT) and Wuhan city (WH) in China.First, SRAP (Sequence-related Amplified Polymorphism) markers and mitochondrial DNA control region sequencing were used to investigate genetic structure of four loach (Misgurnus anguillicaudatus) populations from two sympatric distribution areas of natural diploid and tetraploid loach-Dongting Lake (DT) and Wuhan city (WH) in China. The results from SRAP showed that a total of 534 loci were detected in four loach populations by 18 pairs of polymorphic primer combinations, and the numbers of amplified loci per primer pair ranged from 23 to 40. The averages of Nei’s gene diversity (h) and Shannon’s information index (Ⅰ) of each population were from 0.205 to 0.218 and from 0.324 to 0.341, respectively, and there were no significant difference among h-values orⅠ-values of four populations. UPGMA dendrogram tree, which was constructed based on the Nei’s unbiased genetic distances, showed that DT diploid and DT tetraploid populations were firstly clustered into one branch and their relationships were the nearest, then WH tetraploid population was clustered to the branch, and the other branch contained only WH diploid population. Partial sequences of mitochondrial control region (932～935 bp) of 40 individuals representing four loach populations were sequenced. A total of 47 nucleotides were variable, resulting in a total of 29 haplotypes. Nucleotide diversities (π) of DT tetraploid and DT diploid within populations were 0.898% and 0.872%, respectively, and they were significantly larger than those of WH tetraploid (π=0.465%) and WH diploid (π=0.675%). Within the sympatric diploid and tetraploid loach populations, genetic diversity of DT tetraploid was larger than that of DT diploid, and the genetic diversity of WH diploid was significantly larger than that of WH tetraploid. Analysis of molecular variance (AMOVA) indicated that the genetic variation mainly occurred within populations. Significant population subdivision was supported by both of pairwise FST values and Kimura 2-parameter genetic distances between populations, except for no apparent subdivision between DT tetraploid and DT diploid. Phylogenetic tree through Bayesian inference from the control region sequence haplotypes was similar to the genetic relationship among four loach populations revealed by SRAP analysis. The mismatch distribution of haplotypes and the selective neutrality test suggest that four loach populations may have undergone a recent population expansion.Secondly, Mitochondrial DNA cytochrome oxidase subunitⅠsequencing was used to investigate genetic diversity and genetic structure of twelve loach (Misgurnus anguillicaudatus) populations. Partial sequences of Mitochondrial DNA cytochrome oxidase subunitⅠ(654 bp) of 120 individuals representing four loach populations were sequenced. A total of 117 nucleotides were variable, resulting in a total of 65 haplotypes. There was no insertions/deletions site. Average haplotype diversities and nucleotide diversities(π) of the twelve populations were 0.973 and 0.712%, with 16 shared haplotypes. Analysis of molecular variance (AMOVA) indicated that the genetic variation mainly occurred within populations. According to Kimura 2-parameter model to calculate the genetic distance of 12 loach populations was 0.005～0.066. NJ and UPGMA phylogenetic tree based on K 2-p genetic distance showed PYH clustered into a separate group. The UPGMA tree based on genetic distances of the 120 individuals showed that PYH population was the only population grouped a branch alone.