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，进化是不可能的。长期以来，一个物种的突变率一直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，我们首次全面表明，环境温度实际上强烈地决定了突变率。存在一个最佳温度，在该温度下突变率最低。任何一个方向的偏差都会导致这一比率增加。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？为什么这两种极端温度的突变率都会增加？是什么决定了突变率在温度标度上的最佳位置？它是物种特有的常量，还是随着当地温度条件的变化而演变？通过这个项目，我的目标是了解观察到的温度依赖突变率的因果过程，并探索其进化原因和后果。具体地说，将检验两种不同的假设：观察到的突变率增加到低于最佳温度是由于世代长度的原因。氧化冷应激是低温下突变率增加的原因。通过实验将生成时间与温度解耦，验证了这些假设。不同种群在进化过程中所经历的气候条件不同，其突变率的最适温度也不同，因此是局部适应的。替代：突变率的最适温度是一个物种特有的常数。通过确定冷适应和暖适应种群突变率的温度依赖关系，在普通花园设计中验证了这一假设。

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.