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. While 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, while 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 by-pass 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.

在自然环境中，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特征。此前针对这两类要素的研究多为单因素独立分析，二者的交互作用仍有待深入探究。为填补这一研究空白，我们将大肠杆菌（Escherichia coli）的实验室种群置于由pH、过氧化氢（H₂O₂）与氯化钠（NaCl）组合构成的复杂胁迫环境中开展传代选择，该环境的胁迫强度会随机波动，整个实验持续约900代。我们将该波动胁迫选育种群的生长速率及其对应的权衡（trade-off）模式，与在相同实验周期内、仅处于单一组分胁迫恒定环境下选育的种群进行了对比。经波动胁迫选育的种群，在其所经历的全部选择环境中，平均生长速率更高，且生长速率的变异程度更低。但仅在恒定单胁迫环境下选育的种群，会在非选育环境中出现适应性权衡；而经波动胁迫选育的种群则几乎完全规避了跨环境适应性权衡。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。本研究结果表明，环境复杂性与胁迫波动可对进化种群的潜在权衡结构产生显著影响。