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Epistasis mediates the role of negative frequency-dependent selection in bacterial strain structure

Fig 3

The geometry of competitive interactions shapes epistasis and allelic associations in a competition-colonisation trade-off model.

(a) A linear relationship between all the competition parameters leads to additivity in how fitness effects combine across loci and thus no epistasis, see Eq (8). However a concave or a convex geometry will lead to epistasis of constant sign, as shown with solid lines. More complex geometries which are not purely concave or convex can produce epistasis which sign is frequency-dependent. The red dashed line scenario leads to PFDS wherein the most frequent pair of non-overlapping strains (those associated with either positive or negative linkage) is favoured. In contrast, the blue dashed line geometry leads to NFDS at the genotype level, favouring the least frequent pair of strains and thus abolishing allelic associations. D’ trajectories are shown in (b,c) using the parameter sets shown in panel (a), starting from both positive and negative initial D’. Other parameter values: . See Fig K in S1 File Supplementary Information and L in S1 File Supplementary Information for equilibrium LD from simulations for a wider range of parameters.

doi: https://doi.org/10.1371/journal.pcbi.1014083.g003