In both (A) and (B), the domain is initialized with haploid adults containing 5 different alleles, each geographically isolated to 1/5 of the domain, and each adult colored according to its allelic composition. The model is run for 400 generations. In (A), Ladv = 0 km and Ldiff = 10 km. The allelic composition diffuses isotropically away from initial positions, and no allele is favored over others. In (B), Ladv = 4, so larvae preferentially disperse towards positive x (to the right) and the upstream allele quickly dominates the entire domain. Lreten in (B) is 25 km.