Figure 2.

Invasion of the allele for stress susceptibility, causing increased mortality when relative fertility is low, occurs for any value of theta higher than the plotted critical value. (a) The critical value of θ is plotted as a function of r for different values of α, with n=20. (b) The critical value of θ is plotted as a function of r for different values of n, with α=0.2. We studied the population dynamics for different values of r, n, α and θ. The critical value of θ increases as a function of r, α (a) and deme size n (b). That is, invasion requires that variation in fertility within the population (θ) be high enough, and that the population be sufficiently structured (α and n small enough). Invasion occurs more easily when the locus affecting mortality is linked more tightly to the locus inducing low fertility (lower r). μ=0.001, and the expected longevity is 10 mating seasons for stress-susceptible individuals when under stress, and 50 mating seasons for all other individuals.