Factors and processes shaping the temperature dependence of the point mutation rate

突变将变异引入生物体的基因组，因此，没有突变，进化就不可能发生。一个物种的突变率长期以来被认为是一个与环境无关的常数。然而，在最近的一项研究中，我们第一次全面地证明了环境温度实际上强烈地决定了突变率。有一个最佳温度，在此温度下突变率最低。任何一个方向的偏差都会导致速率的增加。这些结果立即提出了几个重要的问题：观察到的最佳曲线背后的过程是什么？是什么过程导致了突变率的变化？为什么两种极端温度下突变率都会增加？是什么决定了最优突变率在温标上的位置？它是物种特有的常数，还是根据当地的温度条件而进化的？在这个项目中，我的目标是了解观察到的突变率的温度依赖性的因果过程，并探索其进化的原因和后果。具体来说，将测试两种不同的假设：观察到的突变率增加到低于最佳温度是由于世代长度。氧化性冷应激是低温下突变率增加的原因。这些假设是通过实验解耦产生时间与温度。种群间突变率的热最优值因其进化过程中所经历的气候而异，具有局地适应性。备选：突变率的热最佳值是一个物种特异性常数。这一假设在一个普通的花园设计中通过确定冷适应和暖适应种群突变率的温度依赖性来验证。

Mutations introduce variation into the genomes of organisms and are thus the process without which evolution would not be possible. The mutation rate of a species has long been considered an environmentally independent constant. However, in a recent study, we were able to comprehensively show for the first time that environmental temperature actually strongly determines the mutation rate. There is an optimum temperature at which the mutation rate is lowest. Deviations in either direction cause the rate to increase. These results immediately raise several important questions: What are the processes behind the observed optimum curve? What processes drive the variation in mutation rate? Why does the mutation rate increase toward both extreme temperatures? What determines the position of the optimum of the mutation rate on the temperature scale? Is it a species-specific constant or does it evolve in response to local temperature conditions? With this project, I aim to understand the causal processes for the observed temperature dependence of the mutation rate and explore its evolutionary causes and consequences. Specifically, two different hypotheses will be tested: The observed increase in mutation rate to lower than optimal temperatures is due to generation length. Oxidative cold stress is responsible for the increase in mutation rate at lower temperatures. These hypotheses are tested by experimentally decoupling generation time from temperature. The thermal optimum of mutation rate differs between populations depending on the climate experienced in their evolution, thus it is locally adapted. Alternative: the thermal optimum of mutation rate is a species-specific constant. This hypothesis is tested in a common-garden design by determining the temperature dependence of the mutation rate of cold-adapted and warm-adapted populations.