Leroi A M, Bennett A F, Lenski R E
Department of Ecology and Evolutionary Biology, University of California, Irvine 92717.
Proc Natl Acad Sci U S A. 1994 Mar 1;91(5):1917-21. doi: 10.1073/pnas.91.5.1917.
Phenotypic acclimation is generally assumed to confer an advantage in the environment that stimulates the response. To test this beneficial acclimation assumption explicitly, we investigated the consequences of temperature acclimation for the fitness of Escherichia coli at two temperatures, 32 degrees C and 41.5 degrees C. Both temperatures permit growth and long-term persistence of the genotypes in serial culture. We found that prior acclimation to 32 degrees C, relative to acclimation to 41.5 degrees C, enhanced fitness at 32 degrees C, consistent with the assumption. But prior acclimation to 41.5 degrees C actually reduced fitness at 41.5 degrees C, relative to acclimation to 32 degrees C. Hence, the assumption that acclimation always confers an advantage is demonstrated to be false. Acclimation to 41.5 degrees C did, however, improve survival at 50 degrees C, a lethal temperature. This protective response has been shown to be associated with the induction of stress proteins. The reduced competitive fitness caused by acclimation at 41.5 degrees C may reflect a physiological burden associated with expression of stress proteins when they are not needed to prevent lethal damage. Whatever the cause, acclimation to the higher temperature decreased competitive fitness at that temperature.
一般认为表型适应能在刺激该反应的环境中赋予某种优势。为了明确检验这种有益适应的假设，我们研究了温度适应对大肠杆菌在32摄氏度和41.5摄氏度这两个温度下适应性的影响。这两个温度都能使这些基因型在连续培养中生长并长期存活。我们发现，相对于适应41.5摄氏度，预先适应32摄氏度能提高在32摄氏度时的适应性，这与该假设相符。但相对于适应32摄氏度，预先适应41.5摄氏度实际上降低了在41.5摄氏度时的适应性。因此，适应总是能赋予优势这一假设被证明是错误的。然而，适应41.5摄氏度确实提高了在50摄氏度（一个致死温度）下的存活率。这种保护反应已被证明与应激蛋白的诱导有关。在41.5摄氏度下适应所导致的竞争适应性降低，可能反映了在不需要应激蛋白来防止致命损伤时，其表达所带来的生理负担。无论原因是什么，适应较高温度都会降低在该温度下的竞争适应性。
