  Cooperation and competition between pathogens can alter the amount of
individuals affected by a co-infection. Nonetheless, the evolution of the
pathogens' behavior has been overlooked. Here, we consider a co-evolutionary
model where the simultaneous spreading is described by a two-pathogen
susceptible-infected-recovered model in an either synergistic or competitive
manner. At the end of each epidemic season, the pathogens species reproduce
according to their fitness that, in turn, depends on the payoff accumulated
during the spreading season in a hawk-and-dove game. This co-evolutionary model
displays a rich set of features. Specifically, the evolution of the pathogens'
strategy induces abrupt transitions in the epidemic prevalence. Furthermore, we
observe that the long-term dynamics results in a single, surviving pathogen
species, and that the cooperative behavior of pathogens can emerge even under
unfavorable conditions.
