Parasite-mediated evolution of the functional part of the MHC in primates

In this study published last year in the Journal of Evolutionary Biology, authors L.Z. Garamszegi and C.L. Nunn set out to test how parasite burden affects MHC polymorphisms with the largest sample size yet for such a comparison. (The authors pulled MHC data from 51 studies and parasite data from 447 studies, ultimately representing data for 41 primate species and 629 different parasites.) First, the relationship between MHC polymorphisms and total parasite richness was examined. MHC polymorphisms were described in terms of nonsynonymous substitution rate at the antigen-binding site (dN-ABS). No relationship was detected between species richness and MHC traits. A second analysis replaced total parasite richness with nematode species richness and actually revealed a positive correlation (between nematode richness and dN-ABS). After controlling for confounding variables such as population size and geographic range, this positive association remained. The authors did however provide a disclaimer, stating that drawing inferences about the strength of such effects would be premature.