Genetic Diversity Of Amur Catfish(Silurus Asotus) Based On Microsatellite Markers And Cytochrome B Sequences

The Amur catfish (Silurus asotus), an economically important catfish in China, which belongs to family Siluridae in Siluriformes, is widely distributed in East Asia. In recent decades, the aquatic biodiversity is facing a great threat due to global climate change and anthropic activities. In China, the aquatic eco-environment is affected by many human factors, such as the hydropower engineering, reclaiming farmland from lakes, point source and non-point source pollution, introduced exotic species and over-exploitation of fisheries, which lead to a decrease in aquatic resources, reduce in living space, deteriorating of living conditions and increase in the number of endangered species. As one of the component of the aquatic biodiversity, the resources of S. asotus are dwindling, and the genetic diversity is the basis of evolutionary potential of species to respond to environmental changes, this becomes an essential pillar in conservation genetics. However, the genetic studies on this species are scarce, especially that was based on nuclear markers. So, the aims of this study are to explore the genetic diversity and structure of S. asotus populations using microsatellite and mitochondrial DNA as molecular markers, in order to establish the foundation for its conservation and utilization of genetic resources. The main results of this research are as follows:1. We isolated and characterized47novel polymorphic and1monomorphic microsatellite loci in the genome of S. asotus using454sequencing. In addition, a cross-species amplification test showed that38(including22poly-and16monomorphic loci) of these48loci could be successfully cross-amplified from a congener species,S. meridionalis. The high success rates of cross-species amplification confirmed that the microsatellite markers developed in S. asotus could be used effectively for other related catfish species. The polymorphic microsatellite markers described here will provide a valuable resource for future work on genetic diversity, population structure, and marker assisted breeding of this species.2. A total of nine polymorphic microsatellite markers were employed to assess the genetic diversity of S. asotus in eight populations from the Pearl River and the upper and middle reaches of the Yangtze River. The results show that the observed and expected heterozygosities of eight populations varied from0.564to0.899and0.6to0.891, respectively, and the polymorphic information content (PIC) varied from0.69to0.81, showing high polymorphism. The diversity and heterozygosity of Yangtze River populations are overall higher than that from the Pearl River. Although the populations from Yunyang and Pingguo may have experience a short-term genetic "bottleneck effect" due to overfishing and other factors, it did not affect their level of genetic diversity. The genetic structure was evaluated by the analysis of gene flow (Nm), genetic differentiation index (FST) and analysis of molecular variance (AMOVA). The results revealed that gene flow between populations is more frequent, most of genetic variation is from different individual within populations, and the genetic relationship among populations is consistent with their geographic distribution.3. Genetic diversity, structure and population evolutionary history was detected within and among more populations of S. asotus in Yangtze River, Pearl River, Liao River and Southeast coastal river systems based on mitochondrial cytochrome b(cytb) gene sequences. The same with microsatellite markers, the variation level was high in these populations, with haplotype diversity (Hd) ranged from0.848-1.0, nucleotide diversity (Pi) ranged from0.0157-0.0024and the average number of nucleotide differences (K) is19.972. Mitochondrial cytb haplotypes of S. asotus can be divided into four lineages. AMOVA analysis indicated that most of the genetic variation was detected among the four mtDNA lineages, suggested that there were four diversiform lineages for S. asotus in the regions. And the four lineages have experienced recent population expansion event in the late Pleistocene (0.04-0.05Ma) due to the combined effects of the global glacial-interglacial climate cycles during Pleistocene (2.6-0.01Ma).In this study, genetic diversity and structure of S. asotus populations were analyzed based on microsatellite marker and cytb sequences. Overall, the genetic diversity of S. asotus was still relatively high and had diversiform lineages distribution. But the resources of S. asotus populations are decreasing, it is necessary to ensure rational development and protect their habitat for their sustainable resources utilization.