Historical contingency in the evolution of antibiotic resistance after decades of relaxed selection

Populations often encounter changed environments that remove selection for the maintenance of particular phenotypic traits. The resulting genetic decay of those traits under relaxed selection reduces an organism’s fitness in its prior environment. However, whether and how such decay alters the subsequent evolvability of a population upon restoration of selection for a previously diminished trait is not well understood. We addressed this question using Escherichia coli strains from the long-term evolution experiment (LTEE) that independently evolved for multiple decades in the absence of antibiotics. We first confirmed that these derived strains are typically more sensitive to various antibiotics than their common ancestor. We then subjected the ancestral and derived strains to various concentrations of these drugs to examine their potential to evolve increased resistance. We found that evolvability was idiosyncratic with respect to initial genotype; that is, the derived strains did not ...

种群常面临环境变化，导致维持特定表型性状的选择压力消失。由此引发的、在放松选择下这些性状的遗传退化，会降低生物体在原环境中的适应度。然而，此类遗传退化是否、以及如何在先前弱化的性状恢复选择压力后改变种群的后续演化潜力，目前尚未得到充分阐释。本研究以长期进化实验（Long-Term Evolution Experiment, LTEE）中的大肠杆菌（Escherichia coli）菌株为研究对象，这些菌株在无抗生素的环境中独立演化了数十年之久。我们首先证实，相较于其共同祖先，这些衍生菌株通常对多种抗生素更为敏感。随后，我们将祖先菌株与衍生菌株暴露于不同浓度的上述抗生素中，以探究它们演化出更高耐药性的潜力。研究发现，演化潜力随初始基因型呈现出特异性差异；换言之，衍生菌株并未……