Fig 8.
The maintenance of a costly CRISPR-Cas system depends on its effectiveness. (A) Fraction of simulations where host and virus coexist and cas genes are maintained after 103 generations (color bar), as a function of a and μ. The small black region at the upper left corner corresponds to viral extinction. The main black region corresponds to the loss of cas genes. (B) The average duration of CAS maintenance in the population. In the white region, where the virus gets extinct, CRISPR becomes useless and cas genes are lost unless periodic reinfections occur. (C) Fraction of encounters between virus and CAS+ hosts with an immune outcome. The dashed line at the bottom corresponds to the innate immunity s = 0.1. The dashed line at the top corresponds to the 90% probability of an immune encounter at which the viral productivity is <1 for the burst size M = 10, causing viral extinction.