Fig 1. Inclusive fitness functions and optima without signalling cost.

(A) G = ½; (B) G = 0.08 (as in [7]). Inclusive fitness functions parameterized by z are shown as yellow curve for parent’s (function u according to Eq 2 without signal cost f(x)) and (blue curve for offspring (function v according to Eq 1 without signal cost f(x)). The x coordinate value of parent’s curve is the parent’s own fitness contribution g(c, z), the y coordinate value is the fitness contribution the offspring (γ h(c, z)); similarly, the x value of the offspring’s curve is the parent’s contribution (ψ g(z)), the y value is the offspring’s own fitness h(c, z). The actual inclusive fitness value is the sum of the appropriate coordinate values, both for parent and offspring. Parameters are Z = 2, γ = 1/2, ψ = ½, U = 1, c = 3. Yellow and blue stars indicate parent’s and offspring’s optima, respectively. Dashed lines are the calculated derivative tangents that touch optima at 45°, indicating maximum fitness. The optimum z value for parent and offspring are not identical: the yellow dot indicates what the parent’s fitness is at the offspring’s optimum z; blue dot is the offspring’s fitness in case of parent’s optimum z.