突变积累(MA)具有深远的生态和进化后果。一个例子是,条件中性突变的积累导致异质栖息地之间的适应性权衡,从而导致种群差异。这里我们建议温度,控制所有生化和生物物理过程的速率,应该在确定突变效应方面发挥关键作用。特别是,温度升高可能会减轻一些影响,不是全部,有害突变并在MA效应中引起更强的环境依赖性。
我们通过测量十种大肠杆菌基因型在十种温度下对六种碳资源的生长性能,对上述假设进行了实验测试,其中十种基因型来自单个祖先菌株并积累了自发突变。我们分析了MA对生长产量的影响的资源依赖性。相对于祖先类型,MA基因型通常显示出降低的生长产量;在中间温度下,降低的幅度较小。在较高温度下,观察到MA对生长性能的影响对资源的依赖性更强。具体来说,当在较低温度下生长时,MA基因型更有可能在所有六种碳资源上显示出受损的生长性能;但仅在某些情况下遭受生长性能损失,不是所有的六个,碳基板在较高的温度。
较高的温度增加了MA引起有条件的中性健身效果的机会,而MA更有可能引起健身损失,而无论在较低温度下的可用资源如何。这一发现对理解人口差异的地理模式可能如何出现有意义,以及保护实践,特别是保护不同的微生境,可以减轻全球变暖的影响。
Mutation accumulation (MA) has profound ecological and evolutionary consequences. One example is that accumulation of conditionally neutral mutations leads to fitness trade-offs among heterogenous habitats which cause population divergence. Here we suggest that temperature, which controls the rates of all biochemical and biophysical processes, should play a crucial role for determining mutational effects. Particularly, warmer temperatures may mitigate the effects of some, not all, deleterious mutations and cause stronger environmental dependence in MA effects.
We experimentally tested the above hypothesis by measuring the growth performance of ten Escherichia coli genotypes on six carbon resources across ten temperatures, where the ten genotypes were derived from a single ancestral strain and accumulated spontaneous mutations. We analyzed resource dependence of MA consequences for growth yields. The MA genotypes typically showed reduced growth yields relative to the ancestral type; and the magnitude of reduction was smaller at intermediate temperatures. Stronger resource dependence in MA consequences for growth performance was observed at higher temperatures. Specifically, the MA genotypes were more likely to show impaired growth performance on all the six carbon resources when grown at lower temperatures; but suffered growth performance loss only on some, not all the six, carbon substrates at higher temperatures.
Higher temperatures increase the chance that MA causes conditionally neutral fitness effects while MA is more likely to cause fitness loss regardless of available resources at lower temperatures. This finding has implications for understanding how geographic patterns in population divergence may emerge, and how conservation practices, particularly protection of diverse microhabitats, may mitigate the impacts of global warming.