SUMMARY Reproduction of RNA viruses is typically error-prone due to the infidelity of their replicative machinery and the usual lack of proofreading mechanisms. The error rates may be close to those that kill the virus. Consequently, populations of RNA viruses are represented by heterogeneous sets of genomes with various levels of fitness. This is especially consequential when viruses encounter various bottlenecks and new infections are initiated by a single or few deviating genomes. Nevertheless, RNA viruses are able to maintain their identity by conservation of major functional elements. This conservatism stems from genetic robustness or mutational tolerance, which is largely due to the functional degeneracy of many protein and RNA elements as well as to negative selection. Another relevant mechanism is the capacity to restore fitness after genetic damages, also based on replicative infidelity. Conversely, error-prone replication is a major tool that ensures viral evolvability. The potential for changes in debilitated genomes is much higher in small populations, because in the absence of stronger competitors low-fit genomes have a choice of various trajectories to wander along fitness landscapes. Thus, low-fit populations are inherently unstable, and it may be said that to run ahead it is useful to stumble. In this report, focusing on picornaviruses and also considering data from other RNA viruses, we review the biological relevance and mechanisms of various alterations of viral RNA genomes as well as pathways and mechanisms of rehabilitation after loss of fitness. The relationships among mutational robustness, resilience, and evolvability of viral RNA genomes are discussed.

概括由于RNA复制机制的不忠实以及通常缺乏校对机制，因此RNA病毒的复制通常容易出错。错误率可能接近杀死病毒的错误率。因此，RNA病毒种群由具有各种适应水平的异类基因组表示。当病毒遇到各种瓶颈并且单个或少数偏离的基因组引发新的感染时，这尤其重要。但是，RNA病毒能够通过保守主要功能元件来保持其身份。这种保守性源自遗传稳健性或突变耐受性，这主要归因于许多蛋白质和RNA元件的功能简并以及阴性选择。另一个相关的机制是遗传损伤后恢复健康的能力，也是基于复制的不忠行为。相反，容易出错的复制是确保病毒可进化性的主要工具。在少数人群中，使衰弱的基因组发生变化的可能性要高得多，因为在缺乏强大竞争者的情况下，低适应基因组可以选择各种轨迹沿健身环境漫游。因此，低适应人群本质上是不稳定的，可以说，先行一步对于绊倒很有用。在本报告中，我们着重于小核糖核酸病毒并考虑了其他RNA病毒的数据，我们综述了病毒RNA基因组的各种变异的生物学相关性和机制，以及失去适应性后的康复途径和机制。变异鲁棒性之间的关系，