Insect-slapping flower stamens help maximize pollination

For several centuries scientists have noticed that, when a visiting insect’s tongue touches the nectar-producing parts of certain flowers, the stamen containing the pollen snaps forward, deterring the insect from lingering longer. Now, a study led by the Central China Normal University (CCNU) in Wuhan has found that this action increases the flowers’ reproductive success, while reducing the costs of insects lingering too long to feed on the flowers’ nectar.

“We tested three scenarios,” said study lead author Deng-Fei Li, a PhD student in Evolution and Ecology at CCNU. “These included whether snapping stamens help flowers by controlling how much pollen each insect takes, filtering out less proficient pollinators, or reducing the amount of nectar taken by each visitor.”

The scientists immobilized the stamen on the flowers of barberry bushes by dipping the flowers’ floral pedicels in an alcoholic solution for 35 to 45 minutes. This alcohol treatment did not seem to deter pollinators. Then, they compared the behavior of insects and the pollination success of flowers with mobile versus immobile stamens, and tracked how efficiently the insects transported the pollen to other flowers.

The analysis revealed that insects visiting flowers with immobilized stamens stayed 3.6 times longer and removed more nectar than those visiting flowers with mobile stamens. Nonetheless, these insects deposited two times fewer pollen grains for each flower visit. Moreover, insects deposited pollen from flowers with mobile stamens on three times more flowers, as well as on flowers further away, thus increasing the likelihood of the plants’ reproductive success.

“Our study helps resolve the mystery of the purpose of insect-triggered movement of flower parts that has troubled botanists since Linnaeus first observed mobile stamen in 1755,” concluded senior author Shuang-Quan Huang, a professor of Evolution and Ecology at CCNU. “We’ve shown that plants use rapidly moving stamens to enhance the turnover of bees and flies on their flowers, thereby reducing their nectar costs per successfully transported pollen grain.”

The study is published in the journal eLife.

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By Andrei Ionescu, Earth.com Staff Writer