Department of Biology, University of Virginia, Charlottesville, Virginia 22904, USA.
Evolution. 2010 May;64(5):1377-85. doi: 10.1111/j.1558-5646.2009.00914.x. Epub 2009 Dec 2.
Studies measuring natural selection acting via different components of fitness may provide insight into such central questions in evolutionary biology as the evolution of life histories and sexual dimorphism. It is often desirable to combine estimates of selection at different episodes to understand how they interact to produce total lifetime selection. When selective episodes are sequential, total directional selection may be calculated by summing directional selection across episodes. However, it is unclear whether lifetime nonlinear (e.g., stabilizing, disruptive, or correlational) selection may be similarly calculated using estimates of quadratic selection from sequential episodes. Here, I show that lifetime quadratic selection depends not only upon the sum total of quadratic selection across episodes but also upon the pattern of directional selection across episodes. In certain cases, the effects of directional selection across episodes may cancel one another, leading to no net directional selection but strong stabilizing selection. This result suggests that true stabilizing selection may be more common than previously thought, especially when the entire life cycle is considered. The equations derived here are easily applicable to empirical data, as is illustrated both with a simulated dataset and with a reanalysis of a study of quadratic selection in dark-eyed juncos.
研究通过不同适应成分的自然选择可以深入了解进化生物学中的核心问题，如生活史和性二型性的进化。通常，希望将不同时期的选择估计值结合起来，以了解它们如何相互作用产生总寿命选择。当选择期是连续的时，可以通过将各期的定向选择相加来计算总定向选择。然而，目前尚不清楚是否可以使用来自连续时期的二次选择估计值来类似地计算寿命非线性（例如，稳定，破坏或相关）选择。在这里，我表明寿命二次选择不仅取决于各期二次选择的总和，而且还取决于各期定向选择的模式。在某些情况下，各期定向选择的影响可能会相互抵消，导致没有净定向选择，但具有强烈的稳定选择。该结果表明，真正的稳定选择可能比以前认为的更为普遍，尤其是在考虑整个生命周期时。此处推导的方程可以很容易地应用于经验数据，这通过模拟数据集和对暗眼灯草雀中二次选择的研究的重新分析得到了说明。
