An ‘Epidemic Diversity’ conceptual model explains how host genetic diversity affects variation in parasite success

According to conventional wisdom, disease transmission rate is usually higher in more genetically homogenous host populations. Previous studies have principally considered how host population genetic diversity impacts the mean of parasite infection performance. However, when considering risks from epidemics and the emergence of novel infectious diseases, variability in parasite success may be just as important as the mean. Here we propose an Epidemic Diversity Model for how host-parasite population genetic diversity influences both the mean and variability in parasite success. We evaluate this conceptual model by re-analysing effect size data from two meta-analyses, including 211 comparisons of high versus low genetic diversity host populations from 48 studies. Our analysis challenges previous understanding by demonstrating that high host population genetic diversity only reduces mean parasite success for specialist parasites with narrow host range, but not for generalist multi-host parasites. We also find that the combination of host range and parasite population genetic diversity determine the effect of host population genetic diversity on the variability in parasite success. These results have important implications for the management of host population genetic diversity for natural populations.