Slower environmental change hinders adaptation from standing genetic variation
Slower environmental change hinders adaptation from standing genetic variation
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DOI：
10.1371/journal.pgen.1007731
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发表时间：
2018-11-01
期刊：
影响因子：
4.5
通讯作者：
Teotonio, Henrique
中科院分区：
文献类型：
--
作者：
Guzella, Thiago S.;Dey, Snigdhadip;Teotonio, Henrique
进化对环境变化的反应取决于在环境退化导致灭绝之前可用于适应的时间。对这种关系的明确测试仅限于微生物，其中适应通常取决于从头突变的顺序固定，不包括基因型与环境适应性相互作用的常设变异，这对大多数自然物种来说都是关键。对于从长期遗传变异进化而来的自然物种，由于遗传漂变或奠基者效应，在最极端环境下的最佳基因型可能在进化过程中丢失，因此可能阻碍对环境变化较慢的适应。为了解决这一假设，我们进行实验进化的线虫秀丽隐杆线虫的自我繁殖人口和发展的推理模型来描述自然选择现存的基因型环境变化下。在环境突变的情况下，我们发现，在最极端的环境中，选择会迅速增加高适应度基因型的频率。相比之下，在逐渐的环境变化下，选择首先有利于在最极端的环境中更差的基因型。我们用第二组进化实验证明，由于环境变化较慢，因此达到最极端环境的时间较长，遗传漂变和创始人效应可能导致最有益基因型的丧失。我们进一步发现，在最极端的环境中，由于最佳基因型之间的干扰，维持现有的遗传变异可以延迟最佳基因型的固定。两者合计，这些结果表明，较慢的环境变化会阻碍适应常设遗传变异，他们支持的理论模型表明，常设的基因型与环境适应相互作用的变化，严重改变了环境变化下的适应的步伐和结果。
Evolutionary responses to environmental change depend on the time available for adaptation before environmental degradation leads to extinction. Explicit tests of this relationship are limited to microbes where adaptation usually depends on the sequential fixation of de novo mutations, excluding standing variation for genotype-by-environment fitness interactions that should be key for most natural species. For natural species evolving from standing genetic variation, adaptation at slower rates of environmental change may be impeded since the best genotypes at the most extreme environments can be lost during evolution due to genetic drift or founder effects. To address this hypothesis, we perform experimental evolution with self-fertilizing populations of the nematode Caenorhabditis elegans and develop an inference model to describe natural selection on extant genotypes under environmental change. Under a sudden environmental change, we find that selection rapidly increases the frequency of genotypes with high fitness in the most extreme environment. In contrast, under a gradual environmental change selection first favors genotypes that are worse at the most extreme environment. We demonstrate with a second set of evolution experiments that, as a consequence of slower environmental change and thus longer periods to reach the most extreme environments, genetic drift and founder effects can lead to the loss of the most beneficial genotypes. We further find that maintenance of standing genetic variation can retard the fixation of the best genotypes in the most extreme environment because of interference between them. Taken together, these results show that slower environmental change can hamper adaptation from standing genetic variation and they support theoretical models indicating that standing variation for genotype-by-environment fitness interactions critically alters the pace and outcome of adaptation under environmental change.