Impacts of infection avoidance for populations affected by sexually transmitted infections

Sexually transmitted infections are ubiquitous in nature and affect many populations. The key process for their transmission is mating, usually preceded by mate choice. Susceptible individuals may avoid mating with infected individuals to prevent infection provided it is recognizable. We show that accounting for infection avoidance significantly alters host population dynamics. We observe bistability between the disease-free and endemic or disease-induced extinction equilibria, significant abrupt reduction in the host population size and disease-induced host extinction. From the population persistence perspective, the best strategy is either not to avoid mating with the infected individuals, to prevent disease-induced host extinction, or to completely avoid mating with the infected individuals, to prevent pathogen invasion. Increasing sterilization efficiency of the infection leads to lower population sizes and reduced effect of mating avoidance. We also find that the disease-free state is more often attained by populations with strong polyandry, whereas a high-density endemic state is more often observed for populations with strong polygyny, suggesting that polygamy rather than monogamy may be promoted in denser host populations.