Distinguishing causes of virulence evolution: reply to Alizon & Michalakis

In a recent study of the symbiosis between bacteria and plasmids, the available evidence suggests that experimental evolution of plasmid virulence was primarily driven by within-host competition caused by superinfection. The data do not exclude the possibility, however, that a trade-off between virulence and infectious transmission to uninfected bacteria also played a minor role.