Department of Biology, McGill University, Montreal, QC, Canada.
J Evol Biol. 2010 Apr;23(4):791-6. doi: 10.1111/j.1420-9101.2010.01945.x. Epub 2010 Feb 9.
The purpose of this experiment was to find out how a population becomes adapted to extremely stressful conditions as its environment deteriorates. We created a deteriorating environment for experimental selection lines of yeast by a stepwise increase in the concentration of salt in the growth medium. After each step, we tested the ability of the lines to grow at a high concentration of salt near the lethal limit for the ancestral strain. We found that mutations enhancing growth in this highly stressful environment began to spread at intermediate salt concentrations. The degree of enhancement was related to effective population size by a power law with a small exponent. The effect size of these mutations also increased with the population size in a similar fashion. From these results, we interpret adaptation to lethal stress as an indirect response to selection for resistance to previous lower levels of stress in a deteriorating environment. This suggests that the pattern of genetic correlation between successively higher levels of stress is an important factor in facilitating evolutionary rescue.
本实验旨在研究当环境恶化时，种群如何适应极端压力条件。我们通过逐步增加生长培养基中的盐浓度，为酵母的实验选择系创造了一个恶化的环境。在每一步之后，我们测试了系在接近祖先菌株致死限制的高盐浓度下生长的能力。我们发现，在这种高度应激环境中增强生长的突变开始在中等盐浓度下传播。增强的程度与有效种群大小呈幂律关系，指数较小。这些突变的效应大小也以类似的方式随种群大小而增加。根据这些结果，我们将对致死压力的适应解释为对恶化环境中先前较低水平压力的抗性选择的间接反应。这表明，在较高水平的压力之间遗传相关性的模式是促进进化拯救的一个重要因素。
