In an experiment funded by the National Science Foundation, the researchers changed the region of a chromosome, thought to be a single gene, that affects the concentration of yellow pigment in petals of monkeyflowers. M. lewisii, the normal favorite of bees, responded with petals of yellow-orange instead of the usual pink. Although its other features flower size, petal shape and amount of nectar were unchanged, the resulting flowers were suddenly being visited 68 times more often by hummingbirds. The flowers were actually shunned by bees, probably because orange is in the spectrum of light they don't see.
In another alteration as part of the experiment, M. cardinalis, usually favored by hummingbirds, responded with petals that were dark pink rather than deep red. These flowers appealed equally to hummingbirds and bees.
Bradshaw and Schemske say altering just the genetic region responsible for the concentration of yellow pigment is much like what might happen during a naturally occurring mutation.
"Perhaps a single mutation having to do with color changed the pollinator milieu back when there was only a single species," Bradshaw says. That one big evolutionary step may then have been followed by many smaller steps triggered by pollinator preferences that led ultimately to different species.
Monkeyflowers, so-called because someone once imagined the face of a monkey in the markings on the blossoms, have been used by researchers interested in ecology and evolution for more than 50 years. The plants readily reveal the effects of crossbreeding and can be planted in native settings so they are useful for experiments.
"A unique aspect of out work is that it combines ecological observations with molecular genetic techniques to elucidate the process of adaptation in natural populations," Schemske says.