Bennett A F, Lenski R E
Department of Ecology and Evolutionary Biology, University of California, Irvine 92697, USA.
EXS. 1997;83:135-54. doi: 10.1007/978-3-0348-8882-0_8.
We studied both phenotypic and evolutionary adaptation to various thermal environments using the bacterium Escherichia coli as an experimental model system. We determined that 42 degrees C was stressful to a bacterial clone adapted to 37 degrees C, based on reductions in both absolute and competitive fitness, as well as induction of a heat stress response. This clone was also used to found replicated populations that were propagated for thousands of generations under several different thermal regimes, including 42 degrees C. Evolutionary adaptation of the populations to 42 degrees C resulted in an increase in both absolute and relative fitness at that temperature, measured respectively as an increase in the number of descendants (and their biovolume) and in competitive ability relative to the ancestral clone. The replicated experimental lineages achieved their evolutionary improvement by several distinct pathways, which produced differential preadaptation to a non-stressful nutrient environment. Adaptation to this stressful temperature entailed neither a change in the ancestral thermal niche nor any pronounced trade-offs in fitness within the thermal niche, contrary to a priori predictions. This study system was several important advantages for evaluating hypotheses concerning the effects of stress on phenotypic and evolutionary adaptation, including the ability to obtain lineages that have evolved in controlled and defined environments, to make direct measurements of fitness and to quantify the degree of stress imposed by different environments.
我们以大肠杆菌作为实验模型系统，研究了其对各种热环境的表型适应和进化适应。基于绝对适合度和竞争适合度的降低以及热应激反应的诱导，我们确定42摄氏度对适应37摄氏度的细菌克隆具有压力。这个克隆还被用于建立多个重复群体，这些群体在包括42摄氏度在内的几种不同热环境下繁殖了数千代。群体对42摄氏度的进化适应导致在该温度下绝对适合度和相对适合度均有所增加，分别以后代数量（及其生物量）的增加以及相对于原始克隆的竞争能力的增加来衡量。这些重复的实验谱系通过几种不同的途径实现了进化改进，这些途径产生了对无压力营养环境的不同预适应。与先验预测相反，适应这种压力温度既没有改变原始的热生态位，也没有在热生态位内的适合度上出现任何明显的权衡。这个研究系统在评估关于压力对表型和进化适应影响的假设方面具有几个重要优势，包括能够获得在受控和明确环境中进化的谱系、直接测量适合度以及量化不同环境施加的压力程度。
