Figure 2.

Trajectories of the beneficial allele (red) for the three modes of convergent adaptation. Populations i and j are under selection with present-day allele frequencies $x_i$ and $x_j$ at a neutral locus, derived from an ancestral population with allele frequency ε. The populations share some amount of drift proportional to $f_{ij}$ before reaching the ancestral population. (A) Independent mutations model. Beneficial mutations, indicated by the orange triangles, occur independently in the selected populations after they have become isolated. Selection begins, indicated by the blue triangles, once the beneficial allele is present in the population. The beneficial allele sweep to fixation in $t_s$ generations. (B) Standing variant model. The beneficial allele is standing at frequency g in the ancestral population. After the selected populations split, it is still standing at frequency g for t generations prior to the onset of selection. (C) Migration model. The beneficial allele arises in population i and begins sweeping in population i. Meanwhile, there is a continuous low level of migration from population i into population j. The beneficial allele establishes in j after δ generations, where it is swept to fixation in $t_s$ generations.