Figure 4. Epistasis-by-environment interaction is prevalent.

a, Frequency distributions of 8,101 epistasis between mutations in four environments. b, Observed mean fitness of mutants carrying a given number of mutations (solid dots) is lower than expected under no epistasis (open diamonds) in each environment. c, Fractions of mutation pairs that exhibit significant G×G×E for each environment pair (nominal P < 0.05, t-test). d, Epistasis measured in Env₂₃ and that measured in Env₃₀ are highly correlated. Pearson's correlation (r) and Spearman's correlation (ρ) are indicated. The red solid line shows the diagonal, whereas the blue dashed line shows the linear regression.