Pollinators can drive evolution of flower traits: study

Oct 15, 2010 By Krishna Ramanujan
A bee forages for nectar while pollinating a foxglove beardtongue (Penstemon digitalis) flower. Image: Amy Parachnowitsch

(PhysOrg.com) -- Pretty flowers aren't produced so we can show them off in vases -- they serve the purpose of attracting such pollinators as bees, butterflies and hummingbirds, which enable them to produce seeds for the next generation.

Now, confirming scientists' assumptions for years, a new Cornell study has proven that such pollinators are agents of natural selection in -- at least in the foxglove beardtongue (Penstemon digitalis) plant.

"It was assumed that pollinators drive evolution on floral traits because pollinators prefer certain floral characteristics," said Andre Kessler, assistant professor of ecology and evolutionary biology and senior author of a paper published recently in the journal New Phytologist. "In this species, we found that pollinators are the agents of selection on flower morphology [a flower's physical characteristics]," he added.

"These findings are important because it is only by understanding the agents of natural selection that we understand why evolutionary change occurs," said Amy Parachnowitsch, Ph.D. '10, the paper's lead author and a former graduate student in Kessler's lab.

To test their theories, the researchers allowed and other insects to pollinate the flowers of 150 beardtongues in a field; they also hand-pollinated every flower on another 150 plants in the same field. Since the hand-pollinated plants were not dependent on pollinators, they acted as a baseline of natural selection by other forces to which open-pollinated plants could be compared. The researchers could then assess whether pollinators were exerting natural selection on seven floral traits tested by comparing the open-pollinated with hand-pollinated plants. If pollinators were driving on floral traits, then they would have found stronger selection in the open-pollinated plants.

In fact, they found that insect- or open-pollinated plants showed statistically stronger selection for two traits: larger and more flowers. The results definitively showed that pollinators were the agents of selection for both these traits.

The researchers also found that for the number of flowers in open-pollinated plants, a phenomenon called stabilizing selection was at work -- just as it isn't good for human babies to be born too big or too small, it was best for plants to have an intermediate number of blossoms in the open-pollinated plants.

Common sense suggests it is always better to have more flowers because having more flowers often leads to more fruits and seeds. However, Kessler said there can be a cost for plants having too many large flowers -- lots of large, showy flowers boosts the odds that flowers end up pollinating other flowers on the same plant. Showy displays can also attract herbivores that eat both seeds and flowers.

The researchers suspect that the stabilizing selection by keeps the beardtongues from evolving to have ever-bigger displays and, thus, plants avoid inbreeding.

The study was funded by the Botanical Society of America, National Science Foundation and Cornell's Department of Ecology and .

Explore further: 'Femme fatale' emerald ash borer decoy lures and kills males

Related Stories

Study of flower color shows evolution in action

Jun 29, 2009

Scientists at UC Santa Barbara have zeroed in on the genes responsible for changing flower color, an area of research that began with Gregor Mendel's studies of the garden pea in the 1850's.

Bees attracted by floral iridescence

Jan 09, 2009

(PhysOrg.com) -- Plants and their pollinators are the focus of ground-breaking research by Dr Heather Whitney, recently appointed Lloyds Fellow in the School of Biological Sciences. Her latest work, carried ...

Probing Question: Why are flowers beautiful?

Jan 24, 2008

In the 1930s, American artist Georgia O'Keefe wrote: "What is my experience of the flower if it is not color?" O'Keefe is best known for her vibrantly colorful close-ups of petals and stamens on large canvases.

Recommended for you

Meteorite that doomed dinosaurs remade forests

1 hour ago

The meteorite impact that spelled doom for the dinosaurs 66 million years ago decimated the evergreens among the flowering plants to a much greater extent than their deciduous peers, according to a study ...

New camera sheds light on mate choice of swordtail fish

3 hours ago

We have all seen a peacock show its extravagant, colorful tail feathers in courtship of a peahen. Now, a group of researchers have used a special camera developed by an engineer at Washington University in ...

App helps homeowners identify spiders

6 hours ago

Each autumn the number of spiders seen indoors suddenly increases as males go on the hunt for a mate. The Society of Biology is launching a new app to help the public learn more about the spiders that will ...

User comments : 0