温度对突变率和种群分化速率影响的实验进化研究

Three hypotheses have been proposed for the effects of temperature on the rates of evolution: (i) shorter generation time, (ii) higher rates of spontaneous mutations, and (iii) stronger natural selection, at higher temperatures. There has been rich evidence for the generation time hypothesis. The mutation rate hypothesis has received much theoretical attentions; and it has been suggested that higher temperatures accelerate metabolic activities and thus yield more free radicals that cause DNA damages. However, empirical evidence has been lacking. The selection strength hypothesis has not been studied rigorously, either theoretically or empirically. Evolutionary biologists have proposed the three hypotheses mostly for explaining the latitude patterns in speciation rates. However, the mechanical bases are individual- and population-level processes. This project is aimed to experimentally testing the mutation rate and selection strength hypotheses, using an experimental evolution approach. Experiments will be carried out with the model bacterium Escherichia coli. First, a mutation accumulation experiment will be performed at several temperatures, followed by whole-genome re-sequencing work to estimate spontaneous mutation rates. We will test the idea derived from the ecological metabolic theory, that is, neutral mutation rate is determined by metabolic energy expended by per unit mass of tissue. Second, we will run an adaptive evolution experiment in laboratory environment that contains multiple substitutive resources and investigate whether or not higher temperature can lead to faster adaptive evolution and stronger within-population diversification.

环境温度影响物种进化速率的可能机制有三个：高温缩短生物世代时间，高温加速自发突变的产生，高温强化自然选择过程。高温缩短世代时间这一观点被普遍接受。关于温度对突变率影响，有一些理论探讨；但是经验证据不足。关于温度是否影响自然选择强度而改变进化速率，尚没有明确的机理讨论，也几乎没有验证工作。进化生物学家提出这些假说的初衷是解释物种形成速率表现出的纬度格局，但这些机制本身是发生在个体和种群水平上的过程。申请者计划以模式微生物大肠杆菌对后两个假说进行实验验证。首先，在多个温度下开展突变累积实验并对进化菌株测序，分析自发突变速率是否受温度影响；对生态代谢理论关于“突变速率由生物个体单位质量消耗的代谢能量决定”这一核心观点进行验证。其次，在含有多个可替代性资源的环境中开展适应性进化实验，研究高温是否导致更快的适应性进化和更强烈的种群内生态位分化。

研究进化速率对温度依赖性的机制，不仅有助于理解生物多样性格局的形成，也有助于预测全球变化的深远影响。该项目针对温度影响进化速率的生理学机制进行了实验研究，有以下主要研究成果。（1）证明了高温可以加速突变产生，并且发现突变率和代谢速率二者对温度的依赖性高度相似，支持代谢生态学理论关于代谢速率决定突变率的预测。（2）首次具体阐述了高温强化有利突变后果并加速自然选择的假说，并给出了实验证据。（3）在一个实验适应辐射系统中证明了高温加速种群分化，也促进多样性的维持。（4）此外也研究了温度通过生态学过程影响种群分化的机制，描述了对抗性种间关系可以降低和强化局域适应的若干可能情形。这些研究发现表明温度本身就是决定进化速率的最普遍最重要的环境因素之一——而不仅仅只是表征了生物可利用能量的影响。也说明在气候变暖情形下生物种群可以通过发生更快适应进化的可能性——温度上升不仅仅意味着有新的选择压力出现，也意味着加速进化过程的基础过程（比如突变的产生）得以强化。该项目迄今在Ecology Letters、Proceedings B等刊物发表论文9篇。

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