Cooper V S, Lenski R E
Center for Microbial Ecology, Michigan State University, East Lansing 48824, USA.
Nature. 2000 Oct 12;407(6805):736-9. doi: 10.1038/35037572.
When organisms adapt genetically to one environment, they may lose fitness in other environments. Two distinct population genetic processes can produce ecological specialization-mutation accumulation and antagonistic pleiotropy. In mutation accumulation, mutations become fixed by genetic drift in genes that are not maintained by selection; adaptation to one environment and loss of adaptation to another are caused by different mutations. Antagonistic pleiotropy arises from trade-offs, such that the same mutations that are beneficial in one environment are detrimental in another. In general, it is difficult to distinguish between these processes. We analysed the decay of unused catabolic functions in 12 lines of Escherichia coli propagated on glucose for 20,000 generations. During that time, several lines evolved high mutation rates. If mutation accumulation is important, their unused functions should decay more than the other lines, but no significant difference was observed. Moreover, most catabolic losses occurred early in the experiment when beneficial mutations were being rapidly fixed, a pattern predicted by antagonistic pleiotropy. Thus, antagonistic pleiotropy appears more important than mutation accumulation for the decay of unused catabolic functions in these populations.
当生物体通过基因适应一种环境时，它们在其他环境中可能会失去适应性。两种不同的群体遗传过程可以产生生态特化——突变积累和拮抗多效性。在突变积累中，突变通过基因漂变在那些不受选择维持的基因中固定下来；对一种环境的适应和对另一种环境适应性的丧失是由不同的突变引起的。拮抗多效性源于权衡，即那些在一种环境中有益的相同突变在另一种环境中是有害的。一般来说，很难区分这些过程。我们分析了在葡萄糖上繁殖20000代的12株大肠杆菌中未使用的分解代谢功能的衰退情况。在那段时间里，有几株大肠杆菌进化出了高突变率。如果突变积累很重要，那么它们未使用的功能应该比其他菌株衰退得更厉害，但未观察到显著差异。此外，大多数分解代谢功能的丧失发生在实验早期，此时有益突变正在迅速固定，这是拮抗多效性所预测的一种模式。因此，对于这些群体中未使用的分解代谢功能的衰退，拮抗多效性似乎比突变积累更重要。
