Evolutionary dynamics of the read-through error rate ρ. (*A*) Coevolution of ρ and of the number of cryptic sequences that are deleterious, *L*_{del}. The optimal value of ρ as a function of *L*_{del}, calculated as the value maximizing Eq. **2** (*Methods*), is represented by a thick gray line, and ρ evolves toward this line when *L*_{del} is fixed. The equilibrium values of *L*_{del} as functions of log_{10}(ρ) are represented by thin lines, for population sizes *N* = 10^{3} and *N* = 10^{5}. *L*_{del} evolves toward these lines when ρ is fixed. The values of ρ and *L*_{del} obtained by simulation are represented by solid crosses (centered on the mean, ±2 SD across replicate populations), each matching the intersection of the thick and one thin line. Movie S1 shows the simulated coevolutionary dynamics. (*B*) The evolved error rate ρ is low in small populations, high in large populations, and bistable for intermediate populations. Solid and open symbols (error bars ±2 SD; *x* values were slightly changed to avoid superposition) represent the results of simulations starting with (log_{10}(ρ), *L*_{del}) = (−5, 400) and (−2, 0), respectively. (*C*) The ranges of *N* at which ρ is low or bistable increase with the total number of loci, *L*_{tot}. Bistable outcomes were identified by comparing the results of simulations obtained with the same initial conditions as in *B*, using a *t* test with critical value 0.005. Parameter values: γ = 0.01, *p*_{del} = 0.4, *p*_{−}_{del} = 0.1, δ = 10^{−2.5}, μ = 10^{−8}, and *L*_{tot} = 500 (*A* and *B*).

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