Fig. 4.

Starting frequencies of protective alleles necessary to create a Pacific Island population first-contact-like pattern if genetic changes can contribute to a drop in mortality rates. We assumed that heterozygosity and homozygosity for each protective allele provided 100% protection against death from the relevant pathogen (i.e. p_1,ijk = 1, where i > 1, p_2,ijk = 1, where j > 1, etc.). We used Latin Hypercube Sampling to select different starting frequencies for each of the three possible protective alleles, where each allele could start at a frequency between 0 and 1. 25 000 different combinations of starting allele frequencies were tested. Panels (a–f) illustrate combinations of starting allele frequencies (s₁–s₃) which produced a first-contact-like pattern (as described in the Methods section) under six different pathogen mortality scenarios. s₁ is the starting frequency of the allele that protects against the pathogen where R₀ = 1·5; s₂, R₀ = 3·5 and s₃, R₀ = 15. Values of the three pathogen-specific maximum mortality rates, θ₁, θ₂ and θ₃ are given in the title of each panel. In all panels, γ = 0. All other parameters are as given in the Methods section.