As gardeners get busy filling tubs and borders with colourfulbedding plants, scientists at the Universities of Cambridge andBristol have discovered more about what makes flowers attractive tobees rather than humans. Published in the British EcologicalSociety's journal Functional Ecology, their research reveals thatVelcro-like cells on plant petals play a crucial role in helpingbees grip flowers - especially when the wind gets up. The study focuses on special cells found on the surface of petals,whose stunning structure is best seen under an electron microscope.According to lead author, Dr Beverley Glover: "Many of our commongarden flowers have beautiful conical cells if you look closely -roses have rounded conical petal cells while petunias have reallylong cells, giving petunia flowers an almost velvety appearance,particularly visible in the dark-coloured varieties." Glover's group previously discovered that when offered snapdragonswith conical cells and a mutant variety without these cells, beesprefer the former because the conical cells help them grip theflower. "It's a bit like Velcro, with the bee claws locking intothe gaps between the cells," she explains. |
Compared with many garden flowers, however, snapdragons have verycomplicated flowers; bees have to land on a vertical face and pullopen a heavy lip to reach the nectar so Glover was not surprisedthat grip helps. But she wanted to discover how conical cells helpbees visiting much simpler flowers. "Many of our garden flowers like petunias, roses and poppies arevery simple saucers with nectar in the bottom, so we wanted to findout why having conical cells to provide grip would be useful forbees landing on these flowers. We hypothesised that maybe the griphelped when the flowers blow in the wind." Using two types of petunia, one with conical cells and a mutantline with flat cells, Glover let a group of bumblebees that hadnever seen petunias before forage in a large box containing bothtypes of flower, and discovered they too preferred theconical-celled flowers.
They then devised a way of mimicking the way flowers move in thewind. "We used a lab shaking platform that we normally use to mixliquids, and put the flowers on that. As we increased the speed ofshaking, mimicking increased wind speed, the bees increased theirpreference for the conical-celled flowers," she says. The results, Glover says, give ecologists a deeper insight into theextraordinarily subtle interaction between plant and pollinator."Nobody knew what these cells were for, and now we have a goodanswer that works for pretty much all flowers," she concludes."It's is too easy to look at flowers from a human perspective, butwhen you put yourself into the bee's shoes you find hidden featuresof flowers can be crucial to foraging success." Katrina Alcorn, Heather Whitney and Beverley Glover (2012). 'Flowermovement increases pollinator preference for flowers with bettergrip', doi: 10.1111/j.1365-2435.2012.02009.x is published inFunctional Ecology on Tuesday 29 May 2012.
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