Figure 7.

Temperate phage, Mixed presentation. Evolution of lytic superinfection: σ₁₂ is for wild-type phage infecting a mutant lysogen, σ₂₁ is for a mutant phage infecting a wild-type lysogen. (a) Lytic superinfection of a wild-type lysogen by the mutant begins to be favored once the probability of lytic superinfection exceeds ∼ 0.01. The evolution is insensitive to the probability of the wild-type phage lytically superinfecting a mutant lysogen. (b) Adding 10⁸ wild-type lysogens (L₁) per cycle somewhat compresses the intermediate zone of mutant evolution, but there is a slightly increased threshold for the mutant to advance (the dark blue region extends slightly higher). (c) Mutant evolution is expedited when changing both lysogeny and lytic superinfection probabilities together. The effects combined are as expected from their separate effects. Recall that lower values of λ₂ are favored. (d) Adding wild-type lysogens improves joint selection of lysogeny and lytic superinfection probability in some zones but worsens it in others—note the no-evolution zone (dark blue) extends further to the left in (d) than in (c). Parameter values are otherwise as given in Fig. 5