Supplementary Fig. S1.

Change in the mean number of heterozygous SNPs within multiple-genotype infections (MIs) is independent of the threshold used for calling MIs. We examined whether the use of different thresholds (≥1, ≥2 or ≥4 heterozygous SNPs) for categorizing infections as either single-genotype or multiple-genotype infections would have an effect on the association observed between the number of heterozygous SNPs within infections and sampling year. Regardless of whether ≥1, ≥2 or ≥4 heterozygous SNPs were used as the cut-off for defining multiple-genotype infections (MIs), the mean number of heterozygous SNPs within MIs was found to decrease significantly over time (p < 0.05).