Special petal cells help bees get a grip

May 14, 2009

Researchers have discovered why most insect-pollinated flowers have special cone-shaped cells on the surfaces of their petals. They literally help bees get a grip, according to a report published online on May 14th in Current Biology, a publication of Cell Press.

What's more, the researchers also showed that bumblebees will preferentially choose to land on petals that are easier to hold on to. The findings exemplify both the intricacy and the elegant simplicity that can be found in nature, the researchers say.

"I have been studying these cells for many years, and had always wondered whether this simple explanation could be the reason for their presence," said Beverley Glover of the University of Cambridge. "It's great to discover that evolution can be this simple; flowers have evolved to make it easier for pollinators to get a grip on them."

Scientists had long recognized that most flowers have surface cells on their petals, which are shaped like little cones or pyramids. Yet nobody knew what those "conical epidermal cells" were for.

By testing the behavior of bumblebees as they interacted with both replicas of petals and snapdragons differing only in the shape of their petal cells, Glover's team found that the insects can recognize the shape of petal surfaces by touch alone. More importantly, Glover said, they also show that bumblebees will select surfaces with conical cells rather than flat surfaces, because the cones make it easier for them manipulate the flower. This means they can extract nectar from the flower more efficiently.

Glover says that the special cells enable a "Velcro-like" attachment between the pollinators' feet and the flower surface. Without the benefit of those cells, she said, the insects are left "scrabbling and sliding." If the bees were mountaineers, the difference would be akin to climbing a rocky surface versus an ice-covered one, she added.

Glover said she expects that the findings in bumblebees and snapdragons will apply to many other insect-pollinator relationships, noting that about 80 percent of flowers studied have these cells.

"I expect that all pollinators that land - including bees, flies, butterflies, bats, and beetles - will have a preference for these structures," Glover said. "However, flowers that are primarily pollinated by hovering animals -moths and hummingbirds, for instance - might be expected not to bother with these grip-providing surfaces."
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Cell Press

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