Flowers Tailor Petal Iridescence To Suit Bees

Researchers from the University of Cambridge have found that flowers tailor their coloring to a bee's-eye-view, often toning down the iridescence of their petals to attract bees, who in turn spread their pollen around.

The study, led by Professor Beverley Glover from the University of Cambridge's Department of Plant Sciences and Dr. Heather Whitney from the University of Bristol, discovered a subtle amount of iridescence is needed to help bees recognize which flowers are full of nectar. In other words, if there is too much iridescence -- the shiny, color-shifting effect seen on soap bubbles, shells and butterfly wings -- bees get confused as they are unable to distinguish between different shades of purple, for example, and may end up choosing the wrong flower to pollinate.

"In 2009 we showed that some flowers can be iridescent and that bees can see that iridescence, but since then we have wondered why floral iridescence is so much less striking than other examples of iridescence in nature," Glover explained in a news release. "We have now discovered that floral iridescence is a trade-off that makes flower detection by bumblebees easier, but won't interfere with their ability to recognize different colors."

In order to remember which previously visited flowers, of the correct color, are a good source of nectar, bees rely on what researchers call "search images." The idea is that on each foraging trip, bees will retain a mental image of flowers that prove to be a promising source of food.

"So if they find a blue flower that is rich in nectar, they will then visit more blue flowers on that trip rather than hopping between different colors," Glover added. "If you watch a bee on a lavender plant, for example, you'll see it visit lots of lavender flowers and then fly away -- it won't usually move from a lavender flower to a yellow or red flower."

This sort of "visual language," as researchers call it, between the bees and flowers benefits both parties: the insects need nourishment and the plants need help pollinating.

Researchers tested this by creating replica flowers that were too iridescent, naturally iridescent, or non-iridescent. Ultimately, their study revealed bees were much quicker to locate the iridescent flowers than the non-iridescent flowers, and that flowers with too much iridescence impeded the bees' ability to distinguish between the flowers.

"To our eyes most iridescent flowers don't look particularly striking, and we had wondered whether this is simply because flowers aren't very good at producing iridescence," Glover said in the university's release. "But we are not the intended target -- bees are, and they see the world differently from humans."

Their study was recently published in the journal Current Biology.

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