Virulence evolution of a generalist plant virus in a heterogeneous host system

Modelling virulence evolution of multihost parasites in heterogeneous host systems requires knowledge of the parasite biology over its various hosts. We modelled the evolution of virulence of a generalist plant virus, Cucumber mosaic virus (CMV) over two hosts, in which CMV genotypes differ for within-host multiplication and virulence. According to knowledge on CMV biology over different hosts, the model allows for inoculum flows between hosts and for host co-infection by competing virus genotypes, competition affecting transmission rates to new hosts. Parameters of within-host multiplication, within-host competition, virulence and transmission were determined experimentally for different CMV genotypes in each host. Emergence of highly virulent genotypes was predicted to occur as mixed infections, favoured by high vector densities. For most simulated conditions, evolution to high virulence in the more competent Host 1 was little dependent on inoculum flow from Host 2, while in Host 2, it depended on transmission from Host 1. Virulence evolution bifurcated in each host at low, but not at high, vector densities. There was no evidence of between-host trade-offs in CMV life-history traits, at odds with most theoretical assumptions. Predictions agreed with field observations and are relevant for designing control strategies for multihost plant viruses.

在异质宿主系统中开展多宿主寄生虫毒力演化的建模研究，需掌握该寄生虫在不同宿主中的生物学特性。本研究针对一种泛宿主性植物病毒——黄瓜花叶病毒（Cucumber mosaic virus, CMV），在两种宿主中的毒力演化进行建模；其中，CMV不同基因型在宿主体内增殖能力与毒力水平上存在差异。基于CMV在不同宿主中的生物学特性相关研究基础，本模型允许宿主间存在接种体流动，同时支持竞争病毒基因型对宿主的共感染过程，且此类竞争会影响病毒向新宿主的传播效率。针对两种宿主中的不同CMV基因型，我们通过实验测定了宿主体内增殖、宿主体内竞争、毒力以及病毒传播相关的参数。模型预测，高毒力基因型会以混合感染的形式出现，且高媒介密度会对该过程产生促进作用。在多数模拟场景下，传播能力更强的宿主1中，病毒演化至高毒力的过程几乎不受宿主2接种体流动的影响；而宿主2中的高毒力演化则依赖于来自宿主1的病毒传播。在低媒介密度条件下，两种宿主的毒力演化均呈现分叉现象，但在高媒介密度下未出现该现象。未发现CMV生活史性状存在宿主间权衡的证据，这与多数现有理论假设相悖。本模型的预测结果与野外观测结果一致，可为多宿主植物病毒的防控策略设计提供参考依据。