But many plants are unable to self-fertilize even when pollinated by hand. For these plants a more likely adaptation is to improve its attractiveness to pollinators by, for instance, increasing the size of the flower petals, or some other change that brings them crowding in.
"My plants did a little of both," said plant researcher Sarah Bodbyl of Michigan State University's W. K. Kellogg Biological Station. She has conducted experiments with an Oregon monkey flower, Mimulus guttatus, to see if they would tend, after a few generations, towards self-pollination with fewer pollinators around -- which they did. They also, perhaps coincidentally, got slightly larger flowers.
In some cases wooing pollinators better could help the pollinators too, Cheptou pointed out. If, for instance, more pollinators are coming because they get more nectar from certain plants, that would be good for the pollinators. But if all they get is a flashier flower to look at, it's more difficult to see any advantage for pollinators, he said.