Department of Ecology and Evolutionary Biology, University of California 321 Steinhaus Hall, Irvine, California, 92697.
Ecol Evol. 2013 Jul;3(7):2103-15. doi: 10.1002/ece3.600. Epub 2013 Jun 4.
Giant viruses contain large genomes, encode many proteins atypical for viruses, replicate in large viral factories, and tend to infect protists. The giant virus replication factories can in turn be infected by so called virophages, which are smaller viruses that negatively impact giant virus replication. An example is Mimiviruses that infect the protist Acanthamoeba and that are themselves infected by the virophage Sputnik. This study examines the evolutionary dynamics of this system, using mathematical models. While the models suggest that the virophage population will evolve to increasing degrees of giant virus inhibition, it further suggests that this renders the virophage population prone to extinction due to dynamic instabilities over wide parameter ranges. Implications and conditions required to avoid extinction are discussed. Another interesting result is that virophage presence can fundamentally alter the evolutionary course of the giant virus. While the giant virus is predicted to evolve toward increasing its basic reproductive ratio in the absence of the virophage, the opposite is true in its presence. Therefore, virophages can not only benefit the host population directly by inhibiting the giant viruses but also indirectly by causing giant viruses to evolve toward weaker phenotypes. Experimental tests for this model are suggested.
巨型病毒含有大型基因组，编码许多非典型病毒蛋白，在大型病毒工厂中复制，并倾向于感染原生生物。巨型病毒复制工厂反过来又可能被所谓的噬病毒体感染，噬病毒体是更小的病毒，会对巨型病毒的复制产生负面影响。一个例子是感染原生生物棘阿米巴的拟菌病毒，而它们自己又被噬病毒体“卫星”感染。本研究使用数学模型研究了该系统的进化动态。虽然模型表明噬病毒体种群将进化到对巨型病毒抑制的程度越来越高，但它进一步表明，由于在广泛的参数范围内存在动态不稳定性，这使得噬病毒体种群容易灭绝。讨论了避免灭绝所需的影响和条件。另一个有趣的结果是，噬病毒体的存在可以从根本上改变巨型病毒的进化过程。在没有噬病毒体的情况下，巨型病毒预计会朝着增加其基本繁殖率的方向进化，而在有噬病毒体的情况下则相反。因此，噬病毒体不仅可以通过抑制巨型病毒直接使宿主种群受益，还可以通过使巨型病毒朝着较弱的表型进化而间接地使宿主种群受益。建议对该模型进行实验测试。
