Bennett Albert F, Lenski Richard E
Department of Ecology and Evolutionary Biology, University of California, Irvine, California, 92697.
Center for Microbial Ecology, Michigan State University, East Lansing, Michigan, 48824-1325.
Evolution. 1997 Feb;51(1):36-44. doi: 10.1111/j.1558-5646.1997.tb02386.x.
Acclimation refers to reversible, nongenetic changes in phenotype that are induced by specific environmental conditions. Acclimation is generally assumed to improve function in the environment that induces it (the beneficial acclimation hypothesis). In this study, we experimentally tested this assumption by measuring relative fitness of the bacterium Escherichia coli acclimated to different thermal environments. The beneficial acclimation hypothesis predicts that bacteria acclimated to the temperature of competition should have greater fitness than do bacteria acclimated to any other temperature. The benefit predicted by the hypothesis was found in only seven of 12 comparisons; in the other comparisons, either no statistically demonstrable benefit was observed or a detrimental effect of acclimation was demonstrated. For example, in a lineage evolutionarily adapted to 37°C, bacteria acclimated to 37°C have a higher fitness at 32°C than do bacteria acclimated to 32°C, a result exactly contrary to prediction; acclimation to 27°C or 40°C prior to competition at those temperatures confers no benefit over 37°C acclimated forms. Consequently, the beneficial acclimation hypothesis must be rejected as a general prediction of the inevitable result of phenotypic adjustments associated with new environments. However, the hypothesis is supported in many instances when the acclimation and competition temperatures coincide with the historical temperature at which the bacterial populations have evolved. For example, when the evolutionary temperature of the population was 37°C, bacteria acclimated to 37°C had superior fitness at 37°C to those acclimated to 32°C; similarly, bacteria evolutionarily adapted to 32°C had a higher fitness during competition at 32°C than they did when acclimated to 37°C. The more surprising results are that when the bacteria are acclimated to their historical evolutionary temperature, they are frequently competitively superior even at other temperatures. For example, bacteria that have evolved at either 20°C or 32°C and are acclimated to their respective evolutionary temperatures have a greater fitness at 37°C than when they are acclimated to 37°C. Thus, acclimation to evolutionary temperature may, as a correlated consequence, enhance performance not only in the evolutionary environment, but also in a variety of other thermal environments.
驯化是指由特定环境条件诱导的表型可逆的、非遗传的变化。一般认为驯化能提高生物体在诱导其发生变化的环境中的功能（有益驯化假说）。在本研究中，我们通过测量适应不同热环境的大肠杆菌的相对适合度，对这一假设进行了实验检验。有益驯化假说预测，适应竞争温度的细菌应比适应任何其他温度的细菌具有更高的适合度。该假说所预测的益处仅在12次比较中的7次中被发现；在其他比较中，要么未观察到统计学上可证明的益处，要么证明了驯化具有有害影响。例如，在一个进化上适应37°C的谱系中，适应37°C的细菌在32°C时比适应32°C的细菌具有更高的适合度，这一结果与预测完全相反；在27°C或40°C竞争前适应这些温度，与适应37°C的形态相比并无益处。因此，有益驯化假说作为对与新环境相关的表型调整必然结果的一般性预测必须被摒弃。然而，当驯化温度和竞争温度与细菌种群进化所处的历史温度一致时，该假说在许多情况下得到支持。例如，当种群的进化温度为37°C时，适应37°C的细菌在37°C时比适应32°C的细菌具有更高的适合度；同样，进化上适应32°C的细菌在32°C竞争时比适应37°C时具有更高的适合度。更令人惊讶的结果是，当细菌适应其历史进化温度时，即使在其他温度下它们通常也具有竞争优势。例如，在20°C或32°C进化并适应其各自进化温度的细菌，在37°C时比适应37°C时具有更高的适合度。因此，适应进化温度可能作为一种相关结果，不仅在进化环境中，而且在各种其他热环境中提高性能。
