Whether evolution will be rapid enough to rescue declining populations will depend upon population size, the supply of genetic variation, the degree of maladaptation and the historical direction of selection. We examined whether the level of environmental stress experienced by a population prior to abrupt environmental change affects the probability of evolutionary rescue (ER). Hundreds of populations of two species of yeast, Saccharomyces cerevisiae and Saccharomyces paradoxus were exposed to a range of sublethal concentrations of salt for approximately a hundred generations before transfer to a concentration of salt lethal to the ancestor (150 g l(-1) NaCl). The fitness of surviving populations of both species was a quadratic function of yield: fitness was greatest for large populations that had been selected on low salt concentrations (less than 20 g l(-1) NaCl) and small populations that had adapted to high salt (more than 80 g l(-1) NaCl). However, differences occurred between species in the probability of ER. The frequency of ER was positively correlated with salt concentration for S. cerevisiae, but negatively correlated with salt concentration in S. paradoxus. These results not only demonstrate that past environmental conditions can determine the probability of ER after abrupt environmental change, but also suggest that there may even be differences between closely related species that are worth further exploration.

译文

进化是否足够快以挽救不断下降的种群,将取决于种群规模,遗传变异的供应,适应不良的程度和选择的历史方向。我们检查了在突然的环境变化之前人口经历的环境压力水平是否会影响进化救援 (ER) 的可能性。在转移到对祖先致命的盐浓度 (150g l(-1) NaCl) 之前,将两种酵母,酿酒酵母和悖论酵母的数百个种群暴露于一定范围的亚致死浓度的盐,持续约一百代。两种物种的存活种群的适应性是产量的二次函数: 对于以低盐浓度 (小于20g l(-1) NaCl) 选择的大种群和适应高盐 (大于80g l(-1) NaCl) 的小种群,适应性最高。然而,物种之间的ER概率存在差异。ER的频率与酿酒酵母的盐浓度呈正相关,而与食盐浓度呈负相关。这些结果不仅表明过去的环境条件可以确定环境突然变化后ER的可能性,而且还表明密切相关的物种之间甚至可能存在差异,值得进一步探索。

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