Causation without correlation: parasite-mediated frequency-dependent selection and infection prevalence

Parasite-mediated selection is thought to maintain host genetic diversity for resistance. We might thus expect to find a strong positive correlation between host genetic diversity and infection prevalence across natural populations. Here, we used computer simulations to examine host-parasite coevolution in 20 simi-isolated clonal populations across a broad range of values for both parasite virulence and parasite fecundity. We found that the correlation between host genetic diversity and infection prevalence can be significantly positive for intermediate values of parasite virulence and fecundity. But the correlation can also be weak and statistically non-significant, even when parasite-mediated frequency-dependent selection is the sole force maintaining host diversity. Hence correlational analyses of field populations, while useful, might underestimate the role of parasites in maintaining host diversity.

Automated summary

The study found that there may be a strong positive correlation between host genetic diversity and infection prevalence for intermediate values of parasite virulence and fecundity. However, in field populations, the correlation can be weak and statistically non-significant, even when parasite-mediated frequency-dependent selection is the main force maintaining host diversity. Correlational analyses of field populations might therefore underestimate the role of parasites in maintaining host diversity.