Plants known as 'living fossils' use insects for sex

Oct 5, 2007, 14:55 GMT

Washington - Plants have long had a symbiotic relationship with insects, but the ancient cycad tops the lot using heat, chemistry and food to lure and repel their insect sex-agents like an undulating yo-yo.

The plants, whose fossil record dates back to the time of the dinosaurs about 290 to 250 million years ago, use little bugs called thrips to carry pollen from their male parts to the female, according to an article appearing Friday in the journal Science.

Irene Terry, professor of biology at the University of Utah, and her husband Robert Roemer, a professor of mechanical engineering at the university, carried out the study to uncover the secret of the plant's reproduction system.

Until the study, it was thought that pollination of the cycads was carried out randomly by the wind. But the scientists found that some of the eggs produced were buried too deep to have been thus reached.

Instead, the scientists found that the male 'cone' lures the thrips into its centre to eat its pollen, then heats up to produce a toxic smell that drives them out. The female cone then gives off a more attractive odour to draw the pollen-covered thrips into its midst and become pollinated.

The cycads 'are trading food for sex,' Roemer said. 'Pollen is the only thing these thrips eat, so they totally rely on the plants. And the thrips are the only animals that pollinate the plants.'

Roemer, a mechanical engineer, used his knowledge of heat transfer to help in the study.

Cycads are known as 'living fossils' because of their ancient lineage.