Storz Jay F, Beaumont Mark A, Alberts Susan C
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, 85721, USA.
Mol Biol Evol. 2002 Nov;19(11):1981-90. doi: 10.1093/oxfordjournals.molbev.a004022.
The purpose of this study was to test for evidence that savannah baboons (Papio cynocephalus) underwent a population expansion in concert with a hypothesized expansion of African human and chimpanzee populations during the late Pleistocene. The rationale is that any type of environmental event sufficient to cause simultaneous population expansions in African humans and chimpanzees would also be expected to affect other codistributed mammals. To test for genetic evidence of population expansion or contraction, we performed a coalescent analysis of multilocus microsatellite data using a hierarchical Bayesian model. Markov chain Monte Carlo (MCMC) simulations were used to estimate the posterior probability density of demographic and genealogical parameters. The model was designed to allow interlocus variation in mutational and demographic parameters, which made it possible to detect aberrant patterns of variation at individual loci that could result from heterogeneity in mutational dynamics or from the effects of selection at linked sites. Results of the MCMC simulations were consistent with zero variance in demographic parameters among loci, but there was evidence for a 10- to 20-fold difference in mutation rate between the most slowly and most rapidly evolving loci. Results of the model provided strong evidence that savannah baboons have undergone a long-term historical decline in population size. The mode of the highest posterior density for the joint distribution of current and ancestral population size indicated a roughly eightfold contraction over the past 1,000 to 250,000 years. These results indicate that savannah baboons apparently did not share a common demographic history with other codistributed primate species.
本研究的目的是检验是否有证据表明，在更新世晚期，草原狒狒（东非狒狒）的种群扩张与非洲人类和黑猩猩种群的假定扩张同步。其基本原理是，任何足以导致非洲人类和黑猩猩种群同时扩张的环境事件，预计也会影响其他同域分布的哺乳动物。为了检验种群扩张或收缩的遗传证据，我们使用分层贝叶斯模型对多位点微卫星数据进行了合并分析。马尔可夫链蒙特卡罗（MCMC）模拟用于估计人口统计学和系统发育参数的后验概率密度。该模型旨在允许突变和人口统计学参数在位点间存在差异，这使得检测单个位点异常的变异模式成为可能，这些异常模式可能是由突变动态的异质性或连锁位点上的选择效应导致的。MCMC模拟结果与各基因座间人口统计学参数的零方差一致，但有证据表明，进化最慢和最快的基因座之间的突变率相差10至20倍。模型结果提供了有力证据，表明草原狒狒的种群规模经历了长期的历史衰退。当前和祖先种群规模联合分布的最高后验密度模式表明，在过去1000至25万年中，种群规模大约收缩了八倍。这些结果表明，草原狒狒显然与其他同域分布的灵长类物种没有共同的种群历史。
