Fig 4. Linkage disequilibrium (measured as D′) between resistances in a two drug model with ten assortatively mixing host groups, as a function of the Spearman correlation between antibiotic consumption rates for the two antibiotics across the ten host groups.

For each drug, five of these host groups consume antibiotics at a high rate (τ_high = 0.075 which selects for resistance when μ = 1) and five consume antibiotics at a low rate (τ_low = 0.025 which selects for sensitivity when μ = 1). Consumption rates vary from perfectly anticorrelated (all host groups consuming the first antibiotic at high rate consume the second antibiotic at low rate) to perfectly correlated (all host groups consuming the first antibiotic at a high rate also consume the second antibiotic at a high rate). Left-hand panel: all host groups have the same clearance rate (μ = 1). Middle panel: small variation in clearance rate between host groups (0.5 ≤ μ ≤ 1.5). Each red marker corresponds to one possible configuration of antibiotic consumption and clearance rates (see Methods for details), the black markers represent the average of all possible configurations with the same correlation between antibiotic consumption rates (horizontal jitter is for visualisation purposes only). Right-hand panel: similar to middle panel but with larger variation in clearance rate between host groups (0.25 ≤ μ ≤ 2). Other parameters are β = 2, c_β = 0.95 for both antibiotics, c_μ = 1 for both antibiotics.