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A mathematical model for the spread of multipartite viruses reveals their evolutionary potential

Eugenio Valdano, Susanna Manrubia, Sergio Gómez, Alex Arenas

posted on 26 March 2018

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Multipartite viruses replicate through a puzzling evolutionary strategy. These viruses have their genomes segmented into two or more parts encapsidated in separate particles that propagate independently. The requirement of host co-infection to complete the viral cycle represents a major drawback of this adaptive strategy, while its advantages remain unclear. Still, multipartitism is a successful adaptive solution observed in over 40% of all known viral families, particularly targeting plants. The transition from a monopartite to a bipartite viral form has been described in vitro under conditions of high multiplicity of infection, suggesting that cooperation between defective mutants is a plausible evolutionary pathway towards multipartitism. Here we devise a compartmental model for the spread of a multipartite virus in a population of hosts through vector mediated contacts. Our goal is to disentangle which mechanisms might favor the ecological emergence and persistence of multipartitism. Our analytical and numerical results uncover a rich phenomenology driven by the interplay between viral dynamics, vector driven mobility, and the structure of the host population. In the framework of our model, multipartitism appears as a successful adaptive strategy driven by mobility, that permits the colonization of environments forbidden to the nonsegmented variant. Surprisingly, this is promoted in homogeneous contact networks, which corresponds to the vast majority of farmed plant patterns. This is also in line with the observed rising of multipartitism concomitantly with the agricultural expansion.