Analysis of genetic diversity by the SLAF-seq among the farmed Onychostoma macrolepis populations.

OBJECTIVE: The objective of this study was to examine the genetic diversity within and between farmed populations of Onychostoma macrolepis, and to establish a foundation for enhancing the genetic resources of breeding groups through the introduction of new individuals and crossbreeding. A total of 49 individuals were subjected to sequencing using Specific-Locus Amplified Fragment Sequencing (SLAF-seq), one of the restriction site-associated DNA sequencing technologies. The single nucleotide polymorphisms(SNPs)were identified to conduct the analyzation of phylogeny population structure, principal component and genetic diversity. RESULTS: A total of 853,067 SNPs were identified. The results of the phylogenetic analysis revealed that each sample was genetically clustered into three distinct groups: ZhenPing (ZP), LanGao parents (LG), and their progeny population (LG-F1). Each population was observed to be clustered together. Analysis of population genetic diversity revealed that the observed heterozygosity (Ho) ranged from 0.200 to 0.230, the expected heterozygosity (He) ranged from 0.280 to 0.282, and the polymorphic information content (PIC) ranged from 0.228 to 0.230. These results indicate that the genetic diversity of the population is low and the signs of long-term interbreeding are obvious, but there are differences between the populations, and the genetic diversity of the population can be improved by hybridization in different regions.

Transcriptomic responses to heat stress in gill and liver of endangered Brachymystax lenok tsinlingensis.

Global warming significantly affects fish, particularly cold-water fish, because increased temperature adversely impacts their abilities to grow or reproduce, and eventually influences their fitness or even causes death. To survive, fish may alter their distribution or behavior to avoid the stress, and perhaps acclimate or evolve resistance to the elevated temperature. Brachymystax lenok tsinlingensis is an endangered cold-water species in China, and it has been found to alter the altitudinal distribution, decrease swimming efficiency and develop resistance under heat exposure, which badly impact the continuing conservation work. To better protect them, it is essential to understand how they respond to thermal stress behaviorally and physiologically. Therefore, the fish were exposed to 24.5 °C and based on the time taken for them to lose equilibrium, they were separately sampled as sensitive and tolerant groups. Both gill and liver tissues were collected from both groups for transcriptome sequencing. Sequencing results demonstrated that control and tolerant groups were similar in transcriptomic patterns and sensitive groups differentially expressed more genes than tolerant ones, suggesting the gene expression of tolerant groups may return to base levels as exposure time increased. Tissue differences were the major factor affecting gene expression, and they also displayed different physiological responses to heat stress. Consistent with other studies, heat shock response, immune response, metabolic adjustment and ion transport were found to be triggered after exposed to elevated temperature. The findings would contribute to a better understanding of responding mechanisms of fish to thermal stress and provide guidance for future conservation programs.

De novo assembly and microsatellite marker development of the transcriptome of the endangered Brachymystax lenok tsinlingensis.

BACKGROUND: Brachymystax lenok tsinlingensis is an endemic freshwater fish in Northeast Asia, but experienced a dramatic population decline due to over-exploitation, deteriorated habitats and global climate change. It has been listed as a threatened or endangered species in South Korea and China, respectively. However, the conservation and restoration work in wild B. lenok tsinlingensis populations require large amount of genetic and molecular data to support effective management of genetic resources, while the corresponding information is very limited. OBJECTIVE: This study was conducted to generate transcriptome assembly and annotation, as well as to develop novel microsatellite markers for B. lenok tsinlingensis. METHODS: We collected gill and liver tissues and performed transcriptome sequencing. Then the first transcriptome for B. lenok tsinlingensis was de novo assembled and annotated. Microsatellite markers were searched in the assembled transcripts and characterized within ninety individuals collected from three natural sites. RESULTS: A total of 110,712 protein-coding transcripts were assembled, of which 82,861 transcripts were successfully annotated. This assembly displayed a high level of completeness with retrieving 94% of the single-copy orthologs conserved across vertebrate species. Furthermore, 75,891 microsatellite loci were identified from this transcriptome assembly and 20 polymorphic markers were randomly selected for characterization. CONCLUSIONS: The microsatellite markers and the first transcriptome assembly would provide valuable resources for investigating genetic diversity and phylogeographic structure of wild populations and molecular mechanisms responding to stressful environments (e.g. increased water temperature) to guide future conservation studies and breeding programs.

Population differentiation and genetic diversity of endangered Brachymystax tsinlingensis Li between Yangtze River and Yellow River in China based on mtDNA.

Brachymystax tsinlingensis Li, distributed scatteredly in Qinling Mountains of China, is an ideal material for studies of conservation and phylogeography. In the present study, the genetic variations and phylogeographical patterns of B. tsinlingensis collecting from the Yangtze River (n = 30) and the Yellow River (n = 70) were compared based on 1082-1163 bp control region with partial tRNA and 912 bp cyt b partial sequence of mtDNA. Analysis of variance indicated that a high proportion of the total genetic variance (96.03%) was distributed among populations, supporting strong geographic structuring of mtDNA polymorphism. Ten haplotypes were assigned to two clades that were related to geographic regions. No haplotype shared between geographic populations from the Yangtze River and the Yellow River, and two clades related to geographic regions can be clearly found from phylogenetic analysis by Bayesian approach, one from individuals in the Yangtze River and the other from individuals in the Yellow River, which probably indicated artificial carrying not happened historically. The mitochondrial results revealed an obvious differentiation of genetic structure of B. tsinlingensis between populations of Yellow River and Yangtze River, and the estimated diverge time around 0.20 MY. It was suggested that each of the two evolutionarily distinct groups of B. tsinlingensis should be protected and crossing individuals between two river systems should be avoided for conservation purpose.

Genetic diversity and population structure of Brachymystax lenok tsinlingensis using mitochondrial DNA sequences.

Brachymystax lenok tsinlingensis is an endangered freshwater fish which is endemic to part of China. To investigate its genetic diversity and population structure, mitochondrial cytochrome b gene and D-loop control region were used to analyze samples from five different locations. Fifteen haplotypes were identified; however, no shared haplotypes were observed among different streams. The analysis of molecular variance (AMOVA) results indicated that 77.38% of total variation was attributed to differentiation between populations, whereas 22.62% from variation within populations. The high genetic differentiation among the populations would provide useful information for building natural reserves and artificially releasing cultured juveniles in the future.