With the flip of a single genetic switch, a flower can pull in a whole new set of pollinators. The discovery, reported in the 13 November issue of Nature, demonstrates that a minor mutation may have the potential to split one species in two.
The Sierra Nevada Mountains of California are home to two closely related species of monkeyflower. Although their geographic ranges overlap, the red Mimulus cardinalis are a big hit among hummingbirds, which favor scarlet flowers. But they fly right by the pink Mimulus lewisii, which attracts bumblebees in an equally exclusive relationship.
Petal color for both flowers is heavily influenced by a gene known as YUP, which permits or prevents the deposition of yellow pigments. Researchers Toby Bradshaw of the University of Washington, Seattle, and Douglas Schemske of Michigan State University, East Lansing, realized that a mutation in YUP might change the preference of pollinators. To test their theory, the scientists spliced M. lewisii's YUP gene into M. cardinalis, and vice-versa. The mutant M. lewisii now sported yellow-orange flowers, while the engineered M. cardinalis flowers turned a dark pink. The researchers set out arrays of 50 mutants and 50 wild-type plants in areas where both species normally grow and tracked pollinator visits to each type of flower.
Color is a big selling point for pollinators. Hummingbirds flocked to M. lewisii when it was yellow-orange, chalking up 68-fold more visits than when its flowers were the usual pink. At the same time, bumblebees suddenly became much more attracted to M. cardinalis when it was dark pink, although they ignored the plant when it had standard-issue colors. Together, the findings suggest that a simple color change may have played a major role in switching animal pollinators for some plants, Bradshaw says. That switch would prevent the flow of pollen between differently colored flowers, creating reproductive isolation. Subsequent evolutionary changes would have made the populations even more physically distinct, he says.
"To have an example of how a potential single mutation could make this radical a change in pollinators in nature is exciting," says evolutionary biologist Scott Hodges of the University of California, Santa Barbara. Indeed, similar experiments could help scientists turn back the evolutionary clock and recreate other examples of speciation, says biologist Lawrence Rieseberg of Indiana University, Bloomington.