Analysis of genetic variation among Spinibarbus hollandi in the Pearl River and the Yangtze River based on mitochondrial DNA control region sequences

【Objective】 To characterize the genetic structure and phylogeographic pattern of different populations of Spinibarbus hollandi in the Pearl River and the Yangtze River, in order to provide the scientific basis for the conservation and sustainable utilization of S. hollandi populations resources.【Method】 In this study, 347 S. hollandi samples were collected from 10 populations in the Pearl River(the Zengjiang, Liuxi, Beijiang, Lianjiang, Lijiang, Liujiang and Yujiang rivers) and the Yangtze River(the Changjiang, Ganjiang and Xiangjiang rivers). The mitochondrial DNA(mtDNA) control region sequences from each individual were identified and analyzed. According to the MEGA 6.0, DnaSP 6.10 and Arlequin 3.5 software, the base composition, the locus of variation, genetic distance, nucleotide diversity(π), haplotype diversity(H_d) and genetic variation value(F_st) were calculated. In addition, molecular variation analysis(AMOVA), nucleotide mismatch distribution analysis, neutral test, the construction of a haplotype phylogenetic evolutionary tree and network diagram were also carried out.【Result】 The sequence length of the mtDNA control region was 519 bp, in which T, C, A and G accounted for 32.57%, 19.16%, 32.16% and 16.11%, respectively. A total of 62 mutated loci and 34 haplotypes were detected in the sequences. The average haplotype diversity, nucleotide diversity, genetic distance and F_st were 0.917, 0.0359, 0.0018-0.0790 and -0.0007-0.9978, respectively. 63.46% of the molecular genetic variation of the mtDNA CR was observed in the distinct geographical groups. According to the haplotype phylogenetic evolutionary tree and network diagram, ten S. hollandi populations were divided into three groups, with the populations in the Dongjiang River, Xijiang River and Ganjiang River plus Xiangjiang River distributed in three independent branches. However, the Beijiang River and Liuxi River populations had more overlaps with the Dongjiang River and Xijiang River populations. Among the ten populations, the Fu'S Fs ranged from -1.339 to 23.759, with an average of 9.857, but all P values were greater than 0.05. Tajima's D ranged from -2.613 to 2.824 and was significantly negative in only three populations(P< 0.05). The map of nucleotide mismatch distribution showed a multi-peak pattern, indicating that population expansions did not occur in the Pearl River and Yangtze River.【Conclusion】 The genetic diversity of S. hollandi population is generally low. Therefore, the protection of germplasm resources needs improvement, and populations from the Beijiang River should be taken as a key protection unit. The complex landform results in the obvious geographical isolation of S. hollandi populations in the Pearl River and the Yangtze River, and the obvious differentiation among the populations, and the population shrinkage caused by anthropogenic activities had being formatted. Therefore, it is urgent to take effective protective measures to ensure the S. hollandi resources.