ABSTRACT
Viral co-infection occurs when multiple distinct viral particles infect the same host. This can impact viral evolution through intracellular interactions, complementation, reassortment and recombination. In nature many viral species are found to have a wide range of mechanisms to prevent co-infection, which raises the question of how viral evolution is impacted by this strategic choice. Here, we address this question in a model viral system, the ubiquitous bacteriophage and its host bacteria. Using a stochastic model of phage-host interactions in agent-based simulations, we first characterise the behaviour of neutral mutants and find that co-infection decreases the strength of genetic drift. We then quantify how variations in the phage life history parameters affect viral fitness. Importantly, we find that the growth rate (dis)advantage associated with variations in life history parameters can be dramatically different from the competitive (dis)advantage measured in direct-competition simulations. Additionally, we find that co-infection facilitates the fixation of beneficial mutations and the removal of deleterious ones, suggesting that selection is more efficient in co-infecting populations. We also observe, however, that in populations which allow co-infection, a mutant that prevents it displays a substantial competitive advantage over the rest of the population, and will eventually fix even if it displays a much lower growth rate in isolation. Our findings suggest that while preventing co-infection can have a negative impact on the long-term evolution of a viral population, in the short-term it is ultimately a winning strategy, possibly explaining the prevalence of phage capable of preventing co-infection in nature.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵* df390{at}cam.ac.uk