Data from: The evolution of trade-offs under directional and correlational selection

Using quantitative genetic theory we develop predictions for the evolution of trade-offs in response to directional and correlational selection. We predict that directional selection favoring an increase in one trait in a trade-off will result in change in the intercept but not the slope of the trade-off function, with the mean value of the selected trait increasing and that of the correlated trait decreasing. Natural selection will generally favor an increase in some combination of trait values, which can be represented as directional selection on an index value. Such selection induces both directional and correlational selection on the component traits. Theory predicts that selection on an index value will also change the intercept but not the slope of the trade-off function but because of correlational selection, the direction of change in component traits may be in the same or opposite directions. We test these predictions using artificial selection on the well-established trade-off between fecundity and flight capability in the cricket, Gryllus firmus and compare the empirical results with a priori predictions made using genetic parameters from a separate half-sib experiment. Our results support the predictions and illustrate the complexity of trade-off evolution when component traits are subject to both directional and correlational selection.

本研究基于数量遗传学理论（quantitative genetic theory），针对定向选择（directional selection）与相关选择（correlational selection）作用下的性状权衡（trade-off）演化过程构建预测模型。我们预测：当定向选择倾向于提升某一权衡关系中的单个性状（trait）时，仅会改变该权衡函数（trade-off function）的截距而非斜率，此时被选择性状的均值将上升，而关联性状的均值则会下降。自然选择（natural selection）通常会青睐部分性状值的组合提升，这一过程可被表征为对指数值（index value）的定向选择。此类选择会对组分性状（component traits）同时产生定向选择与相关选择效应。理论预测，对指数值的选择同样仅会改变权衡函数的截距而非斜率；但由于相关选择的存在，组分性状的变化方向可能相同，也可能相反。我们通过对灰褐蟋蟀（Gryllus firmus）中已被广泛验证的繁殖力（fecundity）与飞行能力（flight capability）之间的权衡关系开展人工选择（artificial selection）实验，对上述预测进行验证；同时利用另一项半同胞实验（half-sib experiment）获取的遗传参数生成先验预测（a priori predictions），并将实证结果（empirical results）与该先验预测进行对比。本研究结果支持上述预测，同时阐明了当组分性状同时受到定向选择与相关选择作用时，性状权衡演化过程的复杂性。