Primitive plants use heat and odor to woo pollinating insects

The unusual form of sexual reproduction used by some species of cycads – primeval plants known as “living fossils” – may represent an intermediate step in the evolution of plant pollination, the researchers report in the Friday, Oct. 5 issue of the journal Science.

“People think of plants as just sitting there and looking pretty and sending out some odors to attract pollinators, but these cycads have a specific sexual behavior tuned to repel, attract and deceive the thrips [small flying insects] that pollinate them,” says Irene Terry, research associate professor of biology at the University of Utah and principal author of the study.

The thrips enter male cycad cones to eat the pollen, and get covered by it in the process. The “push-pull pollination” method used by some cycads makes the adult thrips fly away, and then lures them back so that some pollen-laden thrips enter female cycad cones and pollinate them.

"They [cycads] are trading food for sex,” says study co-author Robert Roemer, who is Terry’s husband and a professor of mechanical engineering at the University of Utah. “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.”

As a mechanical engineer, Roemer studies heat transfer within the cycad cones.

Terry and Roemer conducted the study of tropical and subtropical cycads and thrips in Australia with three scientists from the University of Queensland: evolutionary biologist Gimme Walter, organic chemist Chris Moore and insect physiologist Craig Hull.-University of Utah