Suppose a species of grasshopper normally breeds in June and lays its eggs on the young shoots of an annual grass that comes up in June. A mutant female grasshopper in the population produces a batch of eggs that carry a new allele that delays sexual development until August. Her offspring feed on the young shoots of another grass, in the very same habitat, that comes up in August. Her offspring mate successfully with one another producing a new generation of August-mating grasshoppers. The August-mating sub-population of grasshoppers is a good candidate for