Department of Biological Sciences, University of Idaho, Moscow, Idaho 83843, USA.
Genetics. 2012 Feb;190(2):655-67. doi: 10.1534/genetics.111.132134. Epub 2011 Nov 17.
In relating genotypes to fitness, models of adaptation need to both be computationally tractable and qualitatively match observed data. One reason that tractability is not a trivial problem comes from a combinatoric problem whereby no matter in what order a set of mutations occurs, it must yield the same fitness. We refer to this as the bookkeeping problem. Because of their commutative property, the simple additive and multiplicative models naturally solve the bookkeeping problem. However, the fitness trajectories and epistatic patterns they predict are inconsistent with the patterns commonly observed in experimental evolution. This motivates us to propose a new and equally simple model that we call stickbreaking. Under the stickbreaking model, the intrinsic fitness effects of mutations scale by the distance of the current background to a hypothesized boundary. We use simulations and theoretical analyses to explore the basic properties of the stickbreaking model such as fitness trajectories, the distribution of fitness achieved, and epistasis. Stickbreaking is compared to the additive and multiplicative models. We conclude that the stickbreaking model is qualitatively consistent with several commonly observed patterns of adaptive evolution.
在将基因型与适应度相关联时，适应模型既需要在计算上易于处理，又需要与观察到的数据在质量上相匹配。可计算性不是一个微不足道的问题的一个原因来自组合问题，即无论一组突变以何种顺序发生，它都必须产生相同的适应度。我们将其称为簿记问题。由于它们的可交换性质，简单的加性和乘法模型自然地解决了簿记问题。然而，它们预测的适应轨迹和上位模式与实验进化中常见的模式不一致。这促使我们提出一个同样简单的新模型，我们称之为折断棒模型。在折断棒模型下，突变的内在适应度效应通过当前背景与假设边界的距离来缩放。我们使用模拟和理论分析来探索折断棒模型的基本特性，例如适应轨迹、达到的适应度分布和上位性。折断棒模型与加性和乘法模型进行了比较。我们得出结论，折断棒模型在质量上与几种常见的适应性进化模式一致。
