School of Life Sciences, University of Sussex, Brighton, United Kingdom ; Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom.
Centre for Computational Systems Biology, Fudan University, Shanghai, China.
PLoS One. 2014 Jan 7;9(1):e84540. doi: 10.1371/journal.pone.0084540. eCollection 2014.
It is likely that the strength of selection acting upon a mutation varies through time due to changes in the environment. However, most population genetic theory assumes that the strength of selection remains constant. Here we investigate the consequences of fluctuating selection pressures on the quantification of adaptive evolution using McDonald-Kreitman (MK) style approaches. In agreement with previous work, we show that fluctuating selection can generate evidence of adaptive evolution even when the expected strength of selection on a mutation is zero. However, we also find that the mutations, which contribute to both polymorphism and divergence tend, on average, to be positively selected during their lifetime, under fluctuating selection models. This is because mutations that fluctuate, by chance, to positive selected values, tend to reach higher frequencies in the population than those that fluctuate towards negative values. Hence the evidence of positive adaptive evolution detected under a fluctuating selection model by MK type approaches is genuine since fixed mutations tend to be advantageous on average during their lifetime. Never-the-less we show that methods tend to underestimate the rate of adaptive evolution when selection fluctuates.
由于环境的变化，作用于突变的选择强度很可能随时间而变化。然而，大多数群体遗传学理论假设选择强度保持不变。在这里，我们使用 McDonald-Kreitman（MK）风格的方法研究了选择压力波动对适应性进化定量的影响。与之前的工作一致，我们表明，即使突变的预期选择强度为零，选择压力的波动也可以产生适应性进化的证据。然而，我们还发现，在波动选择模型下，有助于多态性和分歧的突变往往在其一生中受到正选择。这是因为偶然波动到正选择值的突变往往比波动到负选择值的突变在种群中达到更高的频率。因此，通过 MK 类型的方法在波动选择模型下检测到的正向适应性进化的证据是真实的，因为固定突变在其一生中平均往往是有利的。尽管如此，我们还是表明，当选择波动时，方法往往会低估适应性进化的速度。
