Figure 17.12: Flower Color and Reproductive Isolation Most Phlox drummondii individuals have pink flowers, but in regions where the species is sympatric with P. cuspidata—which is always pink—most P. drummondii individuals have red flowers. Most pollinators preferentially visit flowers of one color or the other. In this experiment, Donald Levin explored whether flower color acts as a prezygotic isolating mechanism that lessens the chances of hybridization between the two species.a