Data from: Evolution of pleiotropic costs in experimental populations

The fitness of populations adapting to new environments is expected to decline in different environments, but empirical studies often do not lend support for such adaptation costs. We test the idea that the initial fitness of the selected populations in the environment where the cost is estimated is key for interpreting tests of ecological trade-offs. We isolated single clones of the yeast Saccharomyces cerevisiae every ~250 generations from replicate experimental lineages that had been selected during 5000 generations in a glucose-limited environment. We then selected these clones in a galactose-limited environment for ~120 generations. Finally, we estimated single-clone fitness in both environments, before and after selection on galactose. The pleiotropic effects on glucose of selection on galactose evolved from positive to negative as fitness in glucose increased, providing strong support for the importance of initial fitness for determining the sign and magnitude of pleiotropic effects. This demonstrates that the sign of pleiotropic effects for fitness following adaptation to a new environment can change during long-term adaptation to an original environment. We also found no relationship between the size of the fitness changes in galactose and glucose, such that pleiotropic effects in glucose became relatively smaller as the sizes of direct effects on galactose increased.适应新环境的种群在不同环境中的适合度（fitness）本应下降，但实证研究往往并不支持这类适应成本的存在。我们验证了这一假说：在估算适应成本的环境中，被选择种群的初始适合度，是解读生态权衡（ecological trade-offs）检验结果的关键所在。我们从在葡萄糖限制环境中经过5000代选择的重复实验谱系中，每约250代分离出一株酿酒酵母（Saccharomyces cerevisiae）单克隆菌株。随后我们在半乳糖限制环境中对这些单克隆菌株进行约120代的选择培养。最终，我们分别在半乳糖选择培养前后，测定了两种环境下单克隆菌株的适合度。随着葡萄糖环境中适合度的提升，半乳糖选择对葡萄糖环境产生的多效性效应（pleiotropic effects）由正向转变为负向，这为初始适合度在决定多效性效应的方向与强度上的重要性提供了强有力的支撑。这一结果表明，在适应原始环境的长期过程中，种群适应新环境后其适合度相关多效性效应的方向可能发生改变。我们还发现，半乳糖环境与葡萄糖环境中的适合度变化幅度之间不存在关联，即随着对半乳糖环境直接效应幅度的提升，葡萄糖环境中的多效性效应相对减弱。