Data from: Escherichia coli populations adapt to complex, unpredictable fluctuations by minimizing trade-offs across environments

In nature, organisms are simultaneously exposed to multiple stresses (i.e. complex environments) that often fluctuate unpredictably. Although both these factors have been studied in isolation, the interaction of the two remains poorly explored. To address this issue, we selected laboratory populations of Escherichia coli under complex (i.e. stressful combinations of pH, H2O2 and NaCl) unpredictably fluctuating environments for ~900 generations. We compared the growth rates and the corresponding trade-off patterns of these populations to those that were selected under constant values of the component stresses (i.e. pH, H2O2 and NaCl) for the same duration. The fluctuation-selected populations had greater mean growth rate and lower variation for growth rate over all the selection environments experienced. However, whereas the populations selected under constant stresses experienced trade-offs in the environments other than those in which they were selected, the fluctuation-selected populations could bypass the across-environment trade-offs almost entirely. Interestingly, trade-offs were found between growth rates and carrying capacities. The results suggest that complexity and fluctuations can strongly affect the underlying trade-off structure in evolving populations.在自然界中，生物体同时面临多种胁迫（即复杂环境），且这些胁迫往往呈现不可预测的波动。尽管学界已分别对这两类因素开展过独立研究，但二者的交互作用仍未得到充分探索。为解决这一问题，我们在由pH、过氧化氢（H₂O₂）与氯化钠（NaCl）组成的复杂胁迫组合的不可预测波动环境中，对大肠杆菌（Escherichia coli）的实验室种群开展了约900代的选择培养。我们将这些经波动胁迫选择的种群，与在相同时长下、于各单一胁迫因子（即pH、H₂O₂与NaCl）恒定值环境中完成选择的种群的生长速率及相应权衡（trade-off）模式进行了对比。经波动胁迫选择的种群，在所有经历的选择环境中均展现出更高的平均生长速率，且生长速率的变异程度更低。与之相对的是，经恒定胁迫选择的种群在自身适配选择环境之外的其他环境中均出现了权衡效应，而经波动胁迫选择的种群则几乎完全规避了跨环境权衡效应。值得注意的是，研究还发现生长速率与环境容纳量（carrying capacity）之间存在权衡关系。上述结果表明，环境复杂性与波动可显著影响进化种群的内在权衡结构。