Waples Robin S, Gaggiotti Oscar
Northwest Fisheries Science Center, Seattle, WA 98112 USA.
Mol Ecol. 2006 May;15(6):1419-39. doi: 10.1111/j.1365-294X.2006.02890.x.
We review commonly used population definitions under both the ecological paradigm (which emphasizes demographic cohesion) and the evolutionary paradigm (which emphasizes reproductive cohesion) and find that none are truly operational. We suggest several quantitative criteria that might be used to determine when groups of individuals are different enough to be considered 'populations'. Units for these criteria are migration rate (m) for the ecological paradigm and migrants per generation (Nm) for the evolutionary paradigm. These criteria are then evaluated by applying analytical methods to simulated genetic data for a finite island model. Under the standard parameter set that includes L = 20 High mutation (microsatellite-like) loci and samples of S = 50 individuals from each of n = 4 subpopulations, power to detect departures from panmixia was very high ( approximately 100%; P < 0.001) even with high gene flow (Nm = 25). A new method, comparing the number of correct population assignments with the random expectation, performed as well as a multilocus contingency test and warrants further consideration. Use of Low mutation (allozyme-like) markers reduced power more than did halving S or L. Under the standard parameter set, power to detect restricted gene flow below a certain level X (H(0): Nm < X) can also be high, provided that true Nm < or = 0.5X. Developing the appropriate test criterion, however, requires assumptions about several key parameters that are difficult to estimate in most natural populations. Methods that cluster individuals without using a priori sampling information detected the true number of populations only under conditions of moderate or low gene flow (Nm < or = 5), and power dropped sharply with smaller samples of loci and individuals. A simple algorithm based on a multilocus contingency test of allele frequencies in pairs of samples has high power to detect the true number of populations even with Nm = 25 but requires more rigorous statistical evaluation. The ecological paradigm remains challenging for evaluations using genetic markers, because the transition from demographic dependence to independence occurs in a region of high migration where genetic methods have relatively little power. Some recent theoretical developments and continued advances in computational power provide hope that this situation may change in the future.
我们回顾了生态范式（强调人口统计学凝聚性）和进化范式（强调生殖凝聚性）下常用的种群定义，发现没有一个是真正可操作的。我们提出了几个定量标准，可用于确定个体群体在何种情况下差异足够大，从而可被视为“种群”。这些标准在生态范式下的单位是迁移率（m），在进化范式下的单位是每代迁移个体数（Nm）。然后通过将分析方法应用于有限岛屿模型的模拟遗传数据来评估这些标准。在包括L = 20个高突变（微卫星样）位点以及来自n = 4个亚种群中每个亚种群的S = 50个个体样本的标准参数集下，即使在高基因流（Nm = 25）的情况下，检测偏离随机交配的能力也非常高（约100%；P < 0.001）。一种新方法，即将正确的种群分配数量与随机预期进行比较，其表现与多位点列联检验相当，值得进一步考虑。使用低突变（等位酶样）标记比将S或L减半更能降低检测能力。在标准参数集下，只要真实的Nm ≤ 0.5X，检测低于某个水平X（原假设：Nm < X）的受限基因流的能力也可能很高。然而，制定合适的检验标准需要对几个关键参数做出假设，而这些参数在大多数自然种群中很难估计。不使用先验抽样信息对个体进行聚类的方法，仅在中等或低基因流（Nm ≤ 5）的条件下才能检测到真实的种群数量，并且随着位点和个体样本量变小，检测能力会急剧下降。一种基于对成对样本中等位基因频率进行多位点列联检验的简单算法，即使在Nm = 25时也有很高的能力检测到真实的种群数量，但需要更严格的统计评估。对于使用遗传标记进行评估而言，生态范式仍然具有挑战性，因为从人口统计学依赖到独立的转变发生在高迁移区域，而在该区域遗传方法的能力相对较低。最近的一些理论发展以及计算能力的持续进步给未来这种情况可能发生变化带来了希望。
