October 4, 2007 / 8:46 PM / 12 years ago

Primitive plants have hot, stinky sex

CHICAGO (Reuters) - One of Earth’s oldest types of plants, the primitive cycad, uses heavy perfume, heat and a bit of guile to lure tiny insects into a strange pollination dance, U.S. researchers said on Thursday.

“They’re pretty bizarre plants,” said Irene Terry, research associate professor of biology at the University of Utah, whose study appears in the journal Science.

Terry and colleagues from the University of Queensland studied Australian Macrozamia cycads, which are ancient tropical plants with large seed cones that are often taken for palm trees. These plants date back nearly 300 million years.

“They reached their heyday during the age of the dinosaurs, but they are older than dinosaurs,” Terry said in a telephone interview.

During the pollination period, called coning season — which occurs every year or once every several years — the male plants emit a scent to attract flying insects called thrips into their pollen-filled, pine cone-like structures.

Once the thrips have dallied a while — eating and covering their tiny bodies with pollen — male cycads turn up the heat and the stink, literally.

Male cycads can heat their cones up some 25 degrees hotter than the surrounding air, with some males reaching 100 degrees Fahrenheit (38 degrees Celsius).

They also emit a strong odor — the chemical beta-myrcene — which is attractive to thrips at low levels, but becomes repellent at higher concentrations.

The whole process is designed to evict the pollen-covered thrips from the male cones.

That’s where the female cycads, with their more subtle fragrance, offer a more attractive and hospitable environment.

The thrips stumble in, find no food, and leave pollen behind.

“They’re luring them in, not giving them any reward,” Terry said, adding, “The plants are almost behaving to make the pollinator do what they want.”

For many years, researchers thought cycads were pollinated by the wind. But Terry said the cones of these Australian cycads are closed too tightly for that to be the case.

She said understanding complex pollination systems like this may help as scientists try to conserve forests and natural habitats.

“We know a lot about crop pollination,” she said. “But if our interest is to help preserve plants on the planet, we need to understand how these pollination systems work.”

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