Disentangling genetic variance for pathogen avoidance and resistance

Hosts can use avoidance (e.g., behavior) to reduce their contact rates with pathogens; after contact, they can use resistance (e.g., immunity) to reduce the establishment and proliferation of an infection. Because both defenses preserve host fitness and reduce pathogen fitness, we expect that their epidemiological and evolutionary effects will be inter-dependent. This study used a two-locus model to understand the evolution of allelic associations (i.e., linkage disequilibrium) between genes determining levels of avoidance and resistance in the presence of an infectious disease or parasite. We found that polymorphism in both avoidance and resistance was possible, but only for a limited range of parameter values of avoidance and resistance; at equilibrium, avoidance and resistance alleles were negatively associated in these polymorphic populations. However, most commonly, whichever defense was more effective and less costly went to fixation. This result suggests that avoidance and resistance may be more likely to covary negatively across than within populations.