PATHOGEN GROWTH AND VIRULENCE DYNAMICS DRIVE THE HOST EVOLUTION AGAINST COINFECTIONS

ABSTRACT Coinfections, or the simultaneous infection of hosts by multiple pathogens, are widespread in nature with significant negative impacts on global health. Can hosts evolve against such coinfections as effectively as they would against individual pathogens? Also, what roles do individual pathogens play during such evolution? Here, we combined theoretical models and experiments with Tribolium castaneum populations evolving against two coinfecting bacterial pathogens, with contrasting growth and virulence dynamics, to reveal that fast-growing pathogens inflicting rapid mortality surges (i.e., fast-acting) restrict adaptive success against coinfections. While hosts rapidly evolved better survival against slow-growing bacteria causing long-lasting infections, evolution against coinfection was significantly delayed and resembled slow adaptation against fast-acting pathogens. Moreover, limited scopes of immunomodulation against fast-acting pathogens during coinfections can drive the observed adaptive patterns. Overall, we provide new insights into how adaptive dynamics and mechanistic bases against coinfections are critically regulated by individual pathogens’ growth and virulence dynamics.