Yukilevich Roman, Lachance Joseph, Aoki Fumio, True John R
Department of Ecology and Evolution, State University of New York, Stony Brook, New York 11794, USA.
Evolution. 2008 Sep;62(9):2215-35. doi: 10.1111/j.1558-5646.2008.00445.x. Epub 2008 Jun 28.
Gene networks are likely to govern most traits in nature. Mutations at these genes often show functional epistatic interactions that lead to complex genetic architectures and variable fitness effects in different genetic backgrounds. Understanding how epistatic genetic systems evolve in nature remains one of the great challenges in evolutionary biology. Here we combine an analytical framework with individual-based simulations to generate novel predictions about long-term adaptation of epistatic networks. We find that relative to traits governed by independently evolving genes, adaptation with epistatic gene networks is often characterized by longer waiting times to selective sweeps, lower standing genetic variation, and larger fitness effects of adaptive mutations. This may cause epistatic networks to either adapt more slowly or more quickly relative to a nonepistatic system. Interestingly, epistatic networks may adapt faster even when epistatic effects of mutations are on average deleterious. Further, we study the evolution of epistatic properties of adaptive mutations in gene networks. Our results show that adaptive mutations with small fitness effects typically evolve positive synergistic interactions, whereas adaptive mutations with large fitness effects evolve positive synergistic and negative antagonistic interactions at approximately equal frequencies. These results provide testable predictions for adaptation of traits governed by epistatic networks and the evolution of epistasis within networks.
基因网络可能控制着自然界中的大多数性状。这些基因的突变通常表现出功能性上位相互作用，从而导致复杂的遗传结构以及在不同遗传背景下产生可变的适应性效应。理解上位遗传系统在自然界中如何进化仍然是进化生物学中的重大挑战之一。在此，我们将一个分析框架与基于个体的模拟相结合，以生成关于上位网络长期适应性的新预测。我们发现，相对于由独立进化的基因控制的性状，上位基因网络的适应性通常具有以下特征：选择性清除的等待时间更长、现存遗传变异更低，以及适应性突变的适应性效应更大。这可能导致上位网络相对于非上位系统要么适应得更慢，要么更快。有趣的是，即使突变的上位效应平均而言是有害的，上位网络也可能适应得更快。此外，我们研究了基因网络中适应性突变的上位性质的进化。我们的结果表明，具有小适应性效应的适应性突变通常进化出正协同相互作用，而具有大适应性效应的适应性突变以大致相等的频率进化出正协同和负拮抗相互作用。这些结果为上位网络控制的性状的适应性以及网络内上位性的进化提供了可检验的预测。
