Asymmetric matching allele models: imperfect matching, stability and the impact of mutation

Abstract

Asymmetric matching alleles models assume that each parasite genotype specializes on a matching host genotype to a different degree. We study system behavior of a single locus di-allelic asymmetric matching alleles model. Inline with other investigators, we make the counter-intuitive observation that intermediate levels of asymmetric matching lead the parasite genotype with the lowest fitness in it's matching host genotype to, on average, be at majority frequencies. The parasite genotype with the highest fitness in its matching host keeps the frequency of this matching host low, which keeps its own frequency low. Further analysis of our asymmetric matching alleles model yields three novel predictions. To begin, a facet of asymmetric matching whose study has been avoided involves the fitness implications of imperfect matching. Imperfect matching permits reduced fitness for parasites enacting a cross infection. Under imperfect matching, increasing the relative fitness for cross infections lowers the level of asymmetric matching required for a parasite genotype to have the highest fitness when infecting any host, which would drive this parasite genotype to or near fixation. Having this high fitness parasite genotype near fixation yields a selection pressure within the host population to mitigate parasite success by having a high frequency of the cross infection host genotype. The second model prediction demonstrates that asymmetric matching can lead to increased system stability by dampening oscillations and lowering the amount of mutation needed for stability. Finally, our analysis predicts that the magnitude of antagonism between parasites and hosts has a large effect on the genetic composition and system behavior of the host-parasite system. We find that parasite and host mutation contribute differently to these antagonism-mediated effects. Overall, studying the single locus system behavior of asymmetric matching allele models should allow for better informed future studies concerning the effects that asymmetric matching has on; polymorphism incidence, recombination rate and mutation rate evolution.