Fig. 2.

Classification of fitness landscapes. Column 1 shows five possible shapes for the r-function, and three possible shapes for the q-function. In some cases, these functions have asymptotes, shown as dashed horizontal lines. Columns 2–6 show the fitness (Upper) and substitution (Lower) trajectories for the 15 landscapes that arise through combinations of r − and q-functions. Substitution trajectories for landscapes with q-function of type A, B, and C are shown in green, dark orange, and purple, respectively. In some cases, the fitness or substitution trajectories possess asymptotic slopes, shown as dashed lines in the corresponding color. In these cases, the asymptotic slope equals the asymptotic value of the corresponding r − or q-function (except for the substitution trajectories in case V). Landscapes V-B and V-C both have asymptotically linear substitution trajectories, and therefore fall into the same class.