Forget Flowers: These Ancient Plants Attract Pollinators by Getting Hot
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Some of the earliest plants attracted pollinators by producing heat that made these plants glow with infrared light, according to a new set of experiments.
The work, published in the journal Science, suggests that long before brightly colored flowers evolved, these ancient plants would metabolically rev themselves up when they had pollen at the ready. Nocturnal insects such as beetles could then see that heat from afar and home in on the target.
These heat-producing plants, called cycads, exist today in tropical forests around the world, although they're one of the most endangered plant groups.
"Some people call them dinosaur plants because they were much more dominant when the dinosaurs were around," says Wendy Valencia-Montoya, a cycad expert at Harvard University.
Fossils from over 200 million years ago, compared to cycads that exist today, show that "the plants look exactly the same," she says. "So they haven't changed much in hundreds of millions of years."
They're related to pines, and male and female plants each produce fleshy, pine-cone-like structures that contain the pollen and the seeds. "That's something very unique among this group of ancient plants," says Valencia-Montoya, who says these are the oldest known plants that have pollen.
A couple of centuries ago, botanists noticed that these plants produced heat in their reproductive structures. Compared to the ambient air temperature, they can be hotter by 15 to 25 degrees Fahrenheit, or even more.
"We think of producing heat as something that mammals do, or birds do, but in fact, plants can do it too," she says, although it's not common in the plant world and takes a lot of energy.
[...] To try to understand more about what was going on, Valencia-Montoya and her colleagues painted some pollinating beetles with fluorescent markers to watch when the beetles went to the plant. And they found that the beetles were clearly going to the plant cones when they heated up.
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