Fig 2. Types of KRS-systems that evolved in a fixed, densely populated habitat.

Simulations were initialised with bacteria with random genotypes, and then run until evolutionary steady state was reached. Out of the 2000 simulations in the parameter sweep, 228 resulted in a KRS-system. (A) In 206 runs killer cells (genotype (On, On)), resistant cells (genotype (Off, On)) and sensitive cells (genotype (Off, Off)) coexisted, but no regulation evolved. (B) In 22 runs regulation did evolve, and in most of these (17 runs) coexistence was found between cells that regulate their toxin production but constitutively expresses resistance (genotype (Reg, On)), non-regulating resistant cells (genotype (Off, On)), and sensitive cells (genotype (Off, Off)). Parameter values for the example runs shown here are: (A) L_cue = 3.7, L_tox = 16.5, $R_0^{-1}=0.1$, ${\widehat{b}}_{\mathrm{T}}=0.045$, C_R = 0.12, and C_C = 0.07; (B) L_cue = 6, L_tox = 6, $R_0^{-1}=0.125$, ${\widehat{b}}_{\mathrm{T}}=0.32$, C_R = 0.1, and C_C = 0.02.