【摘要】 以我国特有的濒危裸子植物白豆杉为材料,采用RAPD标记对其分布于浙江、江西、湖南和广西的11个天然种群予以检测,通过贝叶斯法估测了种群的遗传分化程度,并和由其他算法得出的结果进行了比较。求出的θB(Hickory)、GST(Nei)及ΦST(AMOVA)值分别为0.5018、0.5865和0.5436;而经由Shannon指数计算出的种群间遗传多样性所占比例为0.4839,同贝叶斯法估计出的结果最为接近。和其他松杉类植物相比,白豆杉种群间发生了极其显著的遗传分化,这可能是因为:(1)种群长期处于星散分布状态;(2)雌雄异株,而生于林下的雌株经常不能正常受粉;(3)种群取样跨越的地理范围宽广。Mantel检验表明,种群间的遗传分化程度和地理距离之间显著相关(r=0.719,P=0.003)。此外还发现白豆杉的遗传变异水平偏低,推测瓶颈效应和遗传漂变对小种群的作用是造成这一后果的重要因素。对白豆杉种群的保育和管理提出了建议。更多还原

【Abstract】 Random amplified polymorphic DNA（RAPD） markers are a useful tool for plant population genetic studies.However,as these markers are dominant,heterozygotes and homozygotes for a particular locus are indistinguishable as they will produce a band of similar amplification intensity.This makes it impossible to calculate allelic frequencies directly from RAPD profile data and limited their usefulness in the survey of genetic differentiation among plant populations.To obviate this problem,a Bayesian hierarchical model was presented in terms of the classical F-statistics for partitioning genetic diversity as assessed with dominant markers;and,through the use of Markov chain Monte Carlo（MCMC） simulation,the posterior distribution of θ^B,an analogue to F_ST,can be numerically approximated.Pseudotaxus chienii（Taxaceae） is an endangered conifer endemic to China.In this research,11 of its relictual populations located in Zhejiang,Jiangxi,Hunan and Guangxi provinces were examined using RAPD markers.The degree of genetic differentiation among these populations was estimated by Bayesian approaches and several conventional methods as well.With a burn-in of 50000 iterations and sampling run of 250000 iterations from which every 50th sample is retained for posterior calculations,the estimate for θ^B was obtained as 0.5018 and its 95% credible interval is [0.4672,0.5322].The G_ST and Φ_ST values are 0.5865 and 0.5436,respectively.Interestingly,when using Shannon’s index of phenetic diversity to quantify and further partition the amount of genetic diversity,it was found that 48.39% of the total genetic diversity occurred among populations,very close to the θ^B estimate.Comparison with the estimates based on RAPD analyses of other conifer species indicated that a significantly high degree of genetic differentiation occurred among populations of P.chienii,possibly because:（1） its natural distribution has long been restricted in disjunct isolates characteristic of a fragmented population;（2） the species is dioecious,tending to grow under dense canopy,which hinders the female cone from being pollinated;and（3） the sample collection covers almost the entire range of the species,a large geographical distance.Mantel test showed that the degree of population genetic differentiation is significantly related with geographic distance（r=0.719,P=0.003）.In addition,a low level of RAPD variation was revealed within P.chienii.We propose that the low amount of genetic variation is the result of bottleneck effects as well as genetic drift from small population size.In terms of the above results,the development of conservation strategies for P.chienii was discussed.更多还原