60-Second Science

Plant Passion Truly Hot

The male cycad plant's temperature transitions lead to odor changes that first attract and then repel tiny insects, called thrips. And the comings and goings of the thrips fertilize the female cycads. The research was reported in the journal Science. Cynthia Graber reports.

Plants known as cycads are so old they’re sometimes called living fossils. And their sex life was thought to be pretty boring. The male cone—the sexual part of the plant—has pollen. The female cone has eggs. Scientists thought that wind picked up the pollen and eggs and randomly mixed them together. But recent studies showed that the eggs are too tightly packed to blow away, and in fact insects called thrips pollinate the plants. Now cycad sex is turning steamy.
It turns out that the male plants emit a chemical that attracts thrips. Then the cones heat up between 11 and 3 in the afternoon. They can get up to 25 degrees warmer than the surrounding air. As the plants get hotter, that stinky chemical gets stronger and stronger until it’s so overpowering that it drives the thrips out of the male cycads. The pollen carriers fly around, enter the female cones and drop their pollen packages. As the males cool down, the stink dissipates until it reaches levels that are once again thrip-enticing. This process continues until the males have used up their heating energy reserves, and the females are pollinated. And all are worn out.

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