人工养殖与选育对罗氏沼虾遗传多样性的影响

为探讨人工养殖与选择育种对罗氏沼虾(Macrobrachium rosenbergii)遗传多样性的影响,实验测定了孟加拉野生群体、缅甸野生群体、浙江养殖群体、广西养殖群体及选育群体"南太湖2号"共111只罗氏沼虾核糖体转录间隔区2(Internal transcribed spacer 2,ITS2)基因序列,结果发现58个碱基变异位点,定义56个单倍型。在5个群体中,孟加拉野生群体的遗传多样性最高(平均核苷酸差异数K和核苷酸多态性指数Pi分别为7.186和0.0155),依次为缅甸野生群体、浙江养殖群体、广西养殖群体,选育群体"南太湖2号"遗传多样性最低(K和Pi分别为3.032和0.0065)。5个群体间配对Fst分析表明,养殖群体与野生群体遗传分化显著(P<0.01),选育群体"南太湖2号"不仅与野生群体遗传分化显著,同时还与广西养殖群体产生了显著的遗传分化(P<0.01)。系统树显示,孟加拉野生群体和缅甸野生群体聚为一支,浙江养殖群体、广西养殖群体和选育群体"南太湖2号"则聚为另一支。研究结果表明,人工养殖和选育降低了罗氏沼虾的遗传多样性水平,并导致群体间发生了显著的遗传分化。

EFFECT OF ARTIFICIAL CULTURE AND SELECTIVE BREEDING ON THE GENETIC DIVERSITY OF MACROBRACHIUM ROSENBERGII

The giant freshwater prawn(Macrobrachium rosenbergii) is one of the most important crustaceans in inland aquaculture,especially in many tropical and subtropical areas.China has become the largest producer of the giant freshwater prawn in the world.For protecting species resources and then achieving selective breeding,it is necessary to study the effect of artificial culture and selective breeding on the genetic diversity of M.rosenbergii.In this study,the ribosomal internal transcribed spacer 2(ITS2) of 111 individuals from 5 populations(Bengal wild population,Burma wild population,Zhejiang culture population,Guangxi culture population and selected population "South Tailake No.2") were sequenced and analyzed in order to estimate the genetic diversity and genetic differentiation of M.rosenbergii.Genomic DNA was isolated following the standard method from muscle tissue,and then was kept at 20℃.PCR primers were synthesized by Shanghai Generay Biotech Co.,Ltd.The PCR reaction mixture contained 25 μL,thermal cycling consisted of an initial denaturing at 94℃ for 2min,followed by 30 cycles of denaturing at 94℃ with each cycle of 30s,45s annealing at 55℃,and 1min extension at 72℃,and concluded with a final extension at 72℃ for 10min.The PCR products,which were purified and sequenced by Shanghai Generay Biotech Co.,Ltd and analyzed using CLUSTL W,Dna SP 4.10,Mega 4.0 and Arlequin 3.0 softwares.The results showed that 58 variations and 56 haplotypes were revealed in the 111 sequences.The mean contents of A,T,C and G were 21.6%,24.4%,19.5% and 34.6% in ITS2,and the content of G + C was significantly higher than A + T.It was also found that Bengal wild population had the highest genetic diversity with 7.186 for the average of nucleotide differences(K) and 0.0155 for nucleotide diversity(Pi).In decreasing order of genetic diversity,the others were Burma wild population,Zhejiang culture population,Guangxi culture population in turn.And selected population "South Tailake No.2" had the lowest genetic diversity(K and Pi were 3.032 and 0.0065,respectively) among the five populations of M.rosenbergii.Pairwise Fst of control region sequence analysis among five populations showed that there were significant differences between the wild populations and the culture populations(P<0.01).Significant differences were also found not only between selected population "South Tailake No.2" and wild populations,but also between selected populations "South Tailake No.2" and Guangxi culture population(P<0.01).Genealogical tree showed that Bengal wild population and Burma wild population clustered together,Zhejiang culture population,Guangxi culture population and selected population "South Tailake No.2" clustered together.The results indicated that the ITS2 sequence was a good molecular marker for detecting genetic variation of M.rosenbergii populations,in addition,artificial culture and breeding had led to decreases in genetic diversity and significant genetic differentiation among M.rosenbergii populations.After a 4-generation selection,there was clear genetic differentiation between new selected population "South Tailake No.2" and the base population,and the new breed with stable characteristics would lay a foundation for breeding other new varieties.