Compared substitution maps for pairs (56, 57) and (109,110) of the SRK data set (see table 3). Black squares indicate an average number of substitutions greater than 0.9, gray squares indicate an average number lower than 0.9. Only nodes with at least one black square have been depicted for clarity. Two black squares on the same branch indicate a co-substitution event. The map on the left is for pair (56, 57), which is not detected as coevolving. The map on the right is for detected pair (109, 110), exhibiting several cosubstitution events.