| Rhinogobio cylindricus is a kind of small benthic fish which distributes only in the upper reaches of Yangtze River and its branches. Recent years, with the influence of human activities, such as construction of dams, environment pollution, overfishing and invasion of alien species, the diversity of aquatic organisms are facing a new huge challenge. With the completion and operation of the Three Gorges Dam and Xiangjiaba project, its habitat and biomass in the upper reaches of Yangtze River have been severely affected. The population of Rhinogobio cylindricus, according to our investigation, is also sharply reduced in these years. In order to provide effective conservation measures, we should unravel the genetic structure of Rhinogobio cylindricus. In this study, two types of molecular markers (mitochondrial DNA marker and microsatellite marker) have been employed to assess the genetic structure of Rhinogobio cylindricus from Yibin, Wanzhou, Jiangjin and Hejiang, respectively. The main research results are as follow:(1) Sequences of Cyt b were acquired from 122 specimens of Rhinogobio cylindricus with 62 variable sites. Among these specimens,22 haplotype were determined. The average haplotype diversity (Hd) index of the Rhinogobio cylindricus population was 0.716, and the average nucleotide diversity (π) index was 0.01006. Among the four populations, population from Yibin had the highest haplotype diversity index and the nucleotide diversity index. Analysis of the sequences of control region from the 122 specimens suggested 30 haplotype and 60 variable sites. Meanwhile, the average haplotype diversity index was 0.840 and population from Yibin had the highest haplotype diversity index. The average nucleotide diversity index was 0.01278 and population from Wanzhou had the highest nucleotide diversity index. In Hejiang population, the Hd index and n index were relatively lower than other populations possibly due to a small specimens sampling.(2) According to the constructed haplotype network structure diagram and the phylogenetic tree, no specific correlation between the haplotype distribution of Rhinogobio cylindricus and geologic distribution had been determined. AMOVA based on Cyt b and control region suggested that genetic differentiation degree among populations was very low and the genetic differentiation was mainly occurred within populations. The Fst index based on two molecular markers were both negative, which suggested low differentiation among the four populations.(3) Mismatch distribution pattern, Tajima’s test, and Fu’s Fs test were performed based on the data of Cyt b and control region, all these results indicated that the Rhinogobio cylindricus population in our study had not experienced population expansion in history.(4) Nine microsatellite loci were used to analyze the four populations. The number of alleles was between 6.8889 (HJ) and 14.0000 (JJ) with the average 10.3333, which suggested high gene richness. The expected heterozygosity (He) value ranged from 0.7518 (HJ) to 0.7845 (WZ) with the average value 0.7704. The observed heterozygosity (Ho) value ranged from 0.6680 (JJ) to 0.7879 (HJ) with the average value 0.7373. Finally, the polymorphism information content (PIC) value ranged from 0.66784 (HJ) to 0.72903 (WZ) with the average 0.68095, which indicated high polymorphism.(5) The results of AMOVA analysis indicated that most genetic differentiation occurred within populations and only little genetic differentiation happened between populations. The genetic differentiation index Fst was 0.03036, which suggested no significant genetic differentiation existed between the Rhinogobio cylindricus populations. Besides, the results of genetic distance showed that the genetic distance between Wanzhou population and Yibin population was 0.9269, which was the highest. However, genetic distance between Hejiang population and Jiangjin population was 0.7187, which was the lowest. |
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