扬子鳄种群的微卫星DNA多态及其遗传多样性保护对策分析

SSR Polymorphism of Alligator sinesis and Conservation Strategy of Genetic Diversity

扬子鳄 (Alligatorsinensis)是中国特有的珍稀保护动物 ,为保护这一濒危物种 ,我国于 80年代初在安徽宣州先后建立了扬子鳄繁殖研究中心和国家级扬子鳄自然保护区 ,现饲养种群存鳄数量已达 10 0 0 0余头。为了揭示扬子鳄种群的遗传结构 ,共采集了 3 9个个体的样品 ,其中包括 6件剥制标本 ,按代系不同 ,分为野生群、F1代饲养群及F2 代饲养群 ,用微卫星DNA分子标记对其进行研究。分析结果显示 :扬子鳄种群在微卫星水平表现出很低的遗传多样性 ,平均等位基因数A =2 3 8,平均有效等位基因数Ne=1 60 ,平均观察杂合度Ho=0 3 74,平均期望杂合度He=0 3 50 ,平均多态信息含量PIC =0 3 2 7,3个群体间A、Ne、Ho、He、PIC及各微卫星位点等位基因频率分布无显著差异 ,但F2 代饲养群在Ami μ 6和Ami μ 2 2 2两个位点表现出极显著的遗传不平衡。扬子鳄种群遗传多样性水平低下的主要原因是近几十年来种群数量大幅减少造成 ,现阶段应将全部现存的扬子鳄作为一个整体加以保护 ,在建立新的繁殖群体时 ,应考虑保存物种遗传多样性所必需的有效种群大小 。

Chinese alligator,Alligator sinesis,is a critically endangered endemic species under legislative protection.Results of recent investigations revealed that the number of the alligator was continuously declining in the past 50 years and less than 150 individuals were surviving in the wild until 2000.In order to prevent the extinguishing of this species,the Reproductive Research Center of Alligator sinesis and the National Nature Reserve of Alligator sinesis were set up in early 1980 s in Xuanzhou,Anhui Province.After 20 years of breeding efforts,the number of captive individuals has been brought up to more than 10,000 in total.In order to reveal the genetic structure of Chinese alligator population,total of 39 individuals including 7 wild individuals outside of the research center were sampled to construct wild,F_1 and F_2 groups according to their generations,and 10 micorsatellite loci selected from 25 primer pairs originally designed for Alligator mississippiensis were employed for investigating the genetic diversity of Alligator sinesis.The results indicated that,contrasting with Alligator mississippiensis and some other endangered species,Chinese alligator had an extremely low genetic diversity level with A=2.38,N_e=1.60,H_o=0.374,H_e=0.350 and PIC=0.327.There were no significant differences of A,N_e,H_o,H_e,PIC and each SSR locus alleles frequency distribution among 3 groups.However,Hardy-Weinberg equilibrium analysis revealed that F_2 captive group showed a remarkable genetic disequilibrium at loci Ami-μ-6 and Ami-μ-222.The reason accounting for the current genetic status of Chinese alligator is dramatically shrink of the population in past decades.Due to the lack of significant difference between wild group and captive group,all survived Chinese alligator should be treated as one ESU in the next conservation practice.More attention regarding the effective population size and low frequency alleles should be emphasized in genetic management of captive alligators and establishing new separate propagation.