FIGURE 3.

Determination of fitness in the Sprengel–Liebig system. (a) The fitness of a phenotype along the range of the phenotypic variation relative to a certain environmental factor is typically distributed normally following Shelford's law of tolerance (Rozhok & DeGregori, 2015), with a certain value of the expression of a phenotype being optimal (highest fitness) and fitness decreasing progressively in phenotypes that deviate more from the optimal expression (pessima). In multifactorial environments, the fitness of a phenotype will be limited by the factor to which the phenotype is most poorly adapted. Here, factor A (blue curve) is the fitness‐limiting curve for both the evolved and mutant phenotypes. The evolved phenotype has higher fitness. (b) Changes in environment shift the distributions of phenotypes relative to environmental optima and, respectively, phenotype‐altering mutations change the position of the resulting phenotype relative to environmental optima. Both processes can alter both the fitness of a phenotype and the factor that limits the phenotype's fitness. Here, an environmental shift in factors A and B has led to the mutant phenotype gaining fitness advantage of the evolved phenotype. The factor that limits the fitness of the evolved phenotype has also changed. This figure is adapted from (Rozhok & DeGregori, 2015)