Reseаrchers were mоdeling the effects оf repeаted cycles оf isolаtion with occasional interbreeding among five hypothetical fish species (species A, B, C, D, and E) found in two separate lakes (lakes I and II) that are occasionally joined by flooding, as shown in Figure 1. The research team indicated that species A would be considered to be the single common ancestor of species B, C, D, and E. There are two lakes and Lake Roman numeral 1 is to the left of Lake Roman numeral 2. Lake Roman numeral 1 is very small, and contains fish populations A and B. Lake Roman numeral 2 is extremely large and there are three small islands located in Lake Roman numeral 2 on the left side of the lake. The fish populations A, D, and C are along the right side of the lake in that order, and E is on the left side of the lake below the largest island. Figure 1. Current locations of populations of fish species A, B, C, D, and E Which of the following mechanisms could most likely account for the origin of species B in Lake I?