Data from: Adaptive landscapes in evolving populations of Pseudomonas fluorescens

The repeatability of adaptive evolution depends on the ruggedness of the underlying adaptive landscape. We contrasted the relative ruggedness of adaptive landscapes across two environments by measuring the variance in fitness and metabolic phenotype within and among genetically distinct strains of Pseudomonas fluorescens in two environments differing only in the carbon source provided (glucose vs. xylose). Fitness increased in all lines, plateauing in one environment but not the other. The pattern of variance in fitness among replicate lines was unique to the selection environment; it increased over the course of the experiment in xylose but not in glucose. Metabolic phenotypes displayed two results: (1) populations adapted via changes that were distinctive to their selection environment, and (2) endpoint phenotypes were less variable in glucose than in xylose. These results indicate that although the response to selection is highly repeatable at the level of fitness, the underlying genetic routes taken were different for each environment and more variable in xylose. We suggest that this reflects a more rugged adaptive landscape in xylose compared to glucose. Our study demonstrates the utility of using replicate selection lines with different evolutionary starting points to try and quantify the relative ruggedness of adaptive landscapes.适应性演化的可重复性取决于其所依托的适应景观（adaptive landscape）的崎岖程度。本研究通过在仅碳源不同（葡萄糖 vs 木糖）的两种环境中，测量不同遗传背景的荧光假单胞菌（Pseudomonas fluorescens）菌株的适合度与代谢表型在株内及株间的方差，对比了两种环境下适应景观的相对崎岖程度。所有演化谱系的适合度均有所提升，在一种环境中达到适合度平台，另一环境则未出现该现象。重复演化谱系间的适合度方差模式因选择环境而异：在木糖环境中随实验进程逐渐升高，而葡萄糖环境中无此变化趋势。代谢表型分析得到两项结果：(1) 种群通过与其选择环境特异性相关的遗传变异实现适应性演化；(2) 葡萄糖环境下的终末表型变异程度低于木糖环境。上述结果表明，尽管适合度层面的选择响应具有高度可重复性，但不同环境下所采取的潜在遗传路径各不相同，且木糖环境中的遗传路径变异程度更高。我们认为，这一现象反映出木糖环境下的适应景观比葡萄糖环境更为崎岖。本研究证实，采用具有不同演化起始点的重复选择谱系以量化适应景观的相对崎岖程度，是一种切实有效的研究方法。