Wasik Brian R, Bhushan Ambika, Ogbunugafor C Brandon, Turner Paul E
Current Address: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York, 14583.
Evolution. 2015 Jan;69(1):117-25. doi: 10.1111/evo.12544. Epub 2014 Nov 20.
Life-history theory predicts that traits for survival and reproduction cannot be simultaneously maximized in evolving populations. For this reason, in obligate parasites such as infectious viruses, selection for improved between-host survival during transmission may lead to evolution of decreased within-host reproduction. We tested this idea using experimental evolution of RNA virus populations, passaged under differing transmission times in the laboratory. A single ancestral genotype of vesicular stomatitis virus (VSV), a negative-sense RNA Rhabdovirus, was used to found multiple virus lineages evolved in either ordinary 24-h cell-culture passage, or in delayed passages of 48 h. After 30 passages (120 generations of viral evolution), we observed that delayed transmission selected for improved extracellular survival, which traded-off with lowered viral fecundity (slower exponential population growth and smaller mean plaque size). To further examine the confirmed evolutionary trade-off, we obtained consensus whole-genome sequences of evolved virus populations, to infer phenotype-genotype associations. Results implied that increased virus survival did not occur via convergence; rather, improved virion stability was gained via independent mutations in various VSV structural proteins. Our study suggests that RNA viruses can evolve different molecular solutions for enhanced survival despite their limited genetic architecture, but suffer generalized reproductive trade-offs that limit overall fitness gains.
生活史理论预测，在不断进化的种群中，生存和繁殖的性状无法同时达到最大化。因此，对于诸如传染性病毒这样的专性寄生虫而言，在传播过程中提高宿主间生存率的选择可能会导致宿主体内繁殖能力的下降。我们通过在实验室中对RNA病毒群体进行不同传播时间的传代实验进化来验证这一观点。使用水疱性口炎病毒（VSV，一种负链RNA弹状病毒）的单一祖先基因型来建立多个病毒谱系，这些谱系在普通的24小时细胞培养传代或48小时的延迟传代中进化。经过30次传代（病毒进化120代）后，我们观察到延迟传播选择了提高细胞外生存率，但这是以降低病毒繁殖力为代价的（指数种群增长变慢，平均蚀斑大小变小）。为了进一步研究已确认的进化权衡，我们获得了进化病毒群体的全基因组共有序列，以推断表型与基因型的关联。结果表明，病毒生存率的提高并非通过趋同实现；相反，通过VSV各种结构蛋白中的独立突变获得了更高的病毒粒子稳定性。我们的研究表明，RNA病毒尽管其遗传结构有限，但仍可进化出不同的分子解决方案来提高生存率，但会面临普遍的繁殖权衡，从而限制整体适应性的提高。
