Institute of Earth, Life and Environment (ILEE), University of Namur, 61 rue de Bruxelles, Namur, 5000, Belgium.
Integr Comp Biol. 2020 Dec 16;60(6):1544-1557. doi: 10.1093/icb/icaa047.
Epigenetic mechanisms such as DNA methylation modulate gene expression in a complex fashion 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 populations using a bet-hedging strategy.
表观遗传机制（如 DNA 甲基化）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贡献者之一。遗传与表观遗传之间的相互作用是多方面的，而表观遗传变异处于遗传和环境变异的交叉路口，这使得这些机制在适应进化过程中显得尤为重要。DNA 甲基化模式取决于基因型，并可受环境条件的影响而重塑，而跨代的表观遗传遗传已在各种物种中得到报道。另一方面，DNA 甲基化可以影响基因突变率，并直接影响种群的进化潜力。表观遗传变异的起源可以归因于遗传、环境或随机因素。与前两个因素相比，通常较少受到研究的是缺乏任何可预测顺序的变异，但它仍然存在于自然种群中，而随机的表观遗传变异，也称为自发的表观突变，可以维持表型多样性。在这里，探讨了动物中这种随机表观遗传变异性的潜在来源，重点是 DNA 甲基化。迄今为止，量化随机在表观遗传变异性中的重要性仍然是一个挑战。然而，突变率和表观突变率之间的比较表明后者水平很高，这表明自发的表观突变在适应中具有重要作用。随机表观遗传变异性的影响是多方面的：通过影响发育，随后影响表型，随机的表观遗传标记变化可能提供额外的表型多样性，当自然种群面临波动的环境时，这有助于它们。在同基因系和无性繁殖的生物中，可以容忍较差或缺乏遗传多样性。在瓶颈入侵物种种群和采用风险分散策略的种群中，也发现了随机表观遗传变异性在适应中的进一步影响。
