Fig 4.
(A) CRISPR immunity pc is a function of only the ratio of the length L of the CRISPR array and the total number Nt of distinct viral proto-spacers. The graph is obtained by varying the spacer incorporation probability a and the viral mutation rate μ across the range of virus-host coexistence while keeping the rest of the parameters fixed at b = 10−4, d = 0.5, ℓ = 0.05, and s = 0.1. Solid lines are the predictions of equation 1 with the parameter α = 4, which reflects the strength of correlation between spacers and proto-spacers. This correlation seems to be independent of the number Ns of protospacers per virus. (B) Varying the viral burst size M at a fixed Ns shows that the correlation between the spacers and proto-spacers reflected by the parameter α grows roughly linearly with the burst size M.