Epigenetic mechanisms such as DNA methylation modulate gene expression in a complex fashion and are consequently recognized as among the most important contributors to phenotypic variation in natural populations of plants, animals and microorganisms. Interactions between genetics and epigenetics are multifaceted and epigenetic variation stands at the crossroad between genetic and environmental variance, which make these mechanisms prominent in the processes of adaptive evolution. DNA methylation patterns depend on the genotype and can be reshaped by environmental conditions, while transgenerational epigenetic inheritance has been reported in various species. On the other hand, DNA methylation can influence the genetic mutation rate and directly affect the evolutionary potential of a population. The origin of epigenetic variance can be attributed to genetic, environmental or stochastic factors. Generally less investigated than the first two components, variation lacking any predictable order is nevertheless present in natural populations and stochastic epigenetic variation, also referred to spontaneous epimutations, can sustain phenotypic diversity. Here, potential sources of such stochastic epigenetic variability in animals are explored, with a focus on DNA methylation. To this day, quantifying the importance of stochasticity in epigenetic variability remains a challenge. However, comparisons between the mutation and the epimutation rates showed a high level of the latter, suggesting a significant role of spontaneous epimutations in adaptation. The implications of stochastic epigenetic variability are multifold: by affecting development and subsequently phenotype, random changes in epigenetic marks may provide additional phenotypic diversity, which can help natural populations when facing fluctuating environments. In isogenic lineages and asexually reproducing organisms, poor or absent genetic diversity can hence be tolerated. Further implication of stochastic epigenetic variability in adaptation is found in bottlenecked invasive species populations and in populations using a bet-hedging strategy.

中文翻译：

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随机性在动物种群表观遗传变异起源中的作用

DNA 甲基化等表观遗传机制以复杂的方式调节基因表达，因此被认为是植物、动物和微生物自然种群表型变异的最重要因素之一。遗传学和表观遗传学之间的相互作用是多方面的，表观遗传变异处于遗传变异和环境变异之间的十字路口，这使得这些机制在适应性进化过程中变得突出。DNA 甲基化模式取决于基因型，可以被环境条件重塑，而跨代表观遗传已在各种物种中得到报道。另一方面，DNA甲基化会影响基因突变率，直接影响种群的进化潜力。表观遗传变异的起源可归因于遗传、环境或随机因素。通常比前两个组件研究较少，但自然种群中存在缺乏任何可预测顺序的变异，随机表观遗传变异，也称为自发表观突变，可以维持表型多样性。在这里，探索了动物中这种随机表观遗传变异的潜在来源，重点是 DNA 甲基化。直到今天，量化表观遗传变异性中随机性的重要性仍然是一个挑战。然而，突变和表观突变率之间的比较显示后者的高水平，表明自发表观突变在适应中的重要作用。随机表观遗传变异的影响是多方面的：通过影响发育和随后的表型，表观遗传标记的随机变化可能会提供额外的表型多样性，这可以在面临波动的环境时帮助自然种群。因此，在等基因谱系和无性繁殖生物体中，可以容忍遗传多样性差或缺乏。在瓶颈入侵物种种群和使用对冲策略的种群中发现了适应性随机表观遗传变异的进一步含义。