d. Neutral evolution
We found that MHC diversity was significantly associated with genome-wide genetic diversity that should mostly reflect neutral processes. First, the average MHC allelic richness covaried positively with population mean heterozygosity (coefficient=25.4, F=6.57, df = 24, p = 0.02, Fig. 6A). Second, there was a strong positive correlation between MHC divergence between populations, and genome-wide divergence (Mantel test: r = 0.51, p=0.002, Fig. 6B). That is, more closely related populations tended to be more similar at their MHC loci as well.