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 gen...适应性进化的可重复性取决于其背后的适应性景观（adaptive landscape）的崎岖程度。我们通过测量仅碳源不同（葡萄糖 vs 木糖）的两种环境下，遗传背景各异的荧光假单胞菌（Pseudomonas fluorescens）菌株内部及菌株间的适合度与代谢表型方差，对比了两种环境中适应性景观的相对崎岖程度。所有实验谱系的适合度均有所提升，其中一种环境下适合度趋于平稳，另一种则未出现该现象。重复谱系间的适合度方差模式仅与选择环境相关：在木糖环境中，该方差随实验进程逐渐升高，而葡萄糖环境中则无此变化。代谢表型分析得到两项结果：(1) 菌群通过与对应选择环境特异性相关的遗传改变实现适应性进化；(2) 葡萄糖环境下的终点代谢表型方差低于木糖环境。上述结果表明，尽管在适合度层面，选择响应的可重复性较高，但其背后的遗传...