Host phenology can select for multiple stable parasite virulence strategies

Host phenology is an important driver of parasite transmission dynamics and evolution. Prior research has demonstrated that host phenology can drive monocyclic, obligate-killer parasites to evolve an intermediate virulence strategy where all parasites kill their host just before the season ends to limit the death of parasite progeny in the environment. The impact of host seasonality on parasites that are not constrained to a monocyclic life-cycle, however, cannot be inferred from these results. Here we present a mathematical model that demonstrates that many, but not all, seasonal host activity patterns support multiple evolutionarily stable parasite strategies (ESS), although these strategies cannot coexist in the same system. The specific monocyclic and polycyclic parasite evolutionarily stable strategies in each phenological pattern are interspersed with less-fit mono- and polycyclic strategies (evolutionary repellors). The ESS that dominates each system at equilibrium is a function of the strategy of the parasite introduced into the system. The results demonstrate that host phenology can, in theory, maintain diverse parasite strategies among isolated geographic locations.