Genetic Diversity And Phylogeographical Pattern Of Sinibrama Macrops

Sinibrama macrops is a common Cyprinid species belongs to Sinibrama of Cyprinidae,Cultrinae, and lives in freshwater ecosystem south of Yangtze River in Chinese, which isstrictly adapted to freshwater. This fish population is widely distributed throughout QiantangRiver, Ou River, Ling River, Min River, Pearl River and Yangtze River and is notintroduced for aquaculture or fishery enhancement yet, thus the geographic distribution of thisfish followed the pattern of natural evolution, and this species is a favorable materials forstudy phylogeographical pattern of freshwater.In this study, we investigate the genetic structure of S. macrops among three scales(reservior, single basin and the whole distribution areas), and explore the geneticdiversity response of freshwater fish in the process of dispersion, settlement,evolution, bottleneck effect and population dispersion from the aspect of reservoirformation, barrier formation and historical flora development. We aim to understandthe phylogeographical pattern of freshwater fish and the formation mechanism.After our study, some important results and conclusions are as follows:1. Morphological and genetic differences of three S. macrops populations fromQiandaohu Lake were compared by Morphometrics method and mitochondrial controlregion sequence analysis. Based on the results of principal components analysis,specimens clustered together by scatter plots of scores could not be divided. Itindicated that there is no morphological differentiation among all samples fromQiandaohu Lake.27polymorphic sites were detected yielding72haplotypes. NJ treeand network showed that the geographic distribution was ambiguous. There weresimilar base composition among the three populations, and the content of A+T(64.82%) was higher than the content of G+C (35.18%). High genetic variation (h)and low nucleotide diversity (π) were found in the three populations analyzed forD-loop, and the diversity of Fenkou (h=0.968±0.018, π=0.00476±0.00049) was thehighest, Linqi (h=0.968±0.017, π=0.00453±0.00041) was the second, Fuwen (h=0.937±0.037, π=0.00330±0.00035) was the lowest. The values of geneticdifferentiation index (Fst) were lower than0.05and not significant (P>0.05). A stronggene flow among the populations were observed (Nm>4), and the Nm betweenFenkou and Fuwen was highest (Nm=27.40). The results of all supported the threegeographical populations belong to a randomly mating population. Consequently, wesuggest to keep the pattern of gene flow of S. macrops, and reduce the influence ofhuman activities so as to protect this important species in fishery resources.2. The population genetic structure of the metapopulation of a sedantary Cyprinid fishspecies S. macrops was explored in this study based on the analysis on thepolymorphism of mitochondrial control region of fish samples collected from13sitesin Qiantang River, China. The objectives of this study were,1) to analyze the geneticdiversity and its geographic distribution pattern of the metapopulation of S. macropswithin a single river system; and2) to investigate the relationship between fishgenetic diversity and the change of their habitats caused by environmental variationand/or dams, and thus to analyze how the physical and man-made barriers may affectthe genetic structure and gene flow. A924bp segment of the mitochondrial controlregion was sequenced and analyzed in334specimens of S. macrops. Within theanalyzed924bp length sequences,42nucleotides were variable, and a total of72haplotypes were identified. Haplotype diversity (h=0.894±0.033, h=0.724±0.063) andnucleotide diversity (π=0.00330±0.00035, π=0.00263±0.00027) of the populations inLanxi and Shengzhou were lower than those of the other populations. The AMOVAanalysis indicated that the genetic variation mainly occurred within populations ratherthan among populations, however, significant divergence between Shengzhou andother populations did occur as revealed by both of the pairwise Fst values and averagepairwise differences. No geographic clustering was observed in the network,suggesting that there were gene flow between populations except Shengzhoupopulation which had differentiation from mainstream of Qiantang River. ThePairwise mismatch distributions and the results of Tajima’s D-test showed thedifference of demographic history between Shengzhou populations and others. Theestimated range of the expansion time of Shengzhou population was between84kyrBP and126kyr BP. The differentiation of Shengzhou population was considered to bethe result of the transgression and regression in the last interglacial period. As abarrier, the sea separated Qiantang River mainstream and Cao’e River, then causedgenetic differentiation. In addition, in the mainstream, the disruption of gene flow, the genetic divergence and the decline of genetic diversity caused by the dams were notobserved in our research, suggesting that the effect of dams on population distributionpattern of S. macrops was limited.3. In order to explore the population dispersion pattern of S. macrops in the wholedistribution area and to know about the evolution relationship between S. macropspopulation and S. melrosei, we study the genetic structure and phylogeneticrelationship of S. macrops from7basins and S. melrosei from2basins. Resultsindicated that, sequence divergence of mitochondrial control region varied from3%-8%among S. macrops of Pearl River, Yangtze River, Minzhe and S. melrosei ofJiulong River, Pearl River. The genetic differentiation of Sinibrama among fivegeographic districts had achieved the subspecies level. The phylogenetic analysesshowed that Yangtse River was at the centre of evolutionary relationship amongdifferent populations, so Yangtse River may be the origin centre of S. macrops and S.melrosei. Genetic diversity of S. macrops population in Pearl River(h=0.067±0.061,π=0.00007±0.00007) were rather lower which may be introduced to Pearl River byaccident, and to be independent of S. melrosei distributed in Peal River. Minzhepopulation were at one lineage, results of AMOVA, genetic differentiation index(Fst)and net genetic distance(Da) showed that homogeneous degree was higher in basinsof Minzhe, population differentiation occurred in Qiantang River and Jiaoxi, andexpansion time, network structure analysis showed Min River was the dispersal center.Analyzing the genetic structure and population history among Minzhe population, wefound that Min River and Qiantang River had experienced significant dispersion,which were not found in other populations indicating that the basin size couldinfluence the formation of genetic structure. Besides, the genetic relationships amongS. melrosei in Jiulong River and S. macrops were relatively close, this may be causedby the genetic drift in small size river system, which limited mutation and made thepopulation reserve the original haplotype.