Plants That Turn Up the Heat: Cycads’ Steamy Secret to Successful Pollination

Harvard researchers have uncovered evidence that some of the planet’s oldest seed plants use heat, rather than color or scent alone, to communicate with their pollinators — a discovery that reshapes scientists’ understanding of how early plant–animal relationships evolved.

In a new study published as a cover story in Science, the team, led by OEB alum Wendy Valencia-Montoya (PhD '25), reports that cycads, an ancient lineage of seed plants dating back roughly 275 million years, actively heat their reproductive cones to attract beetle pollinators. The beetles, in turn, have evolved specialized infrared-sensitive organs that allow them to detect these thermal signals and shuttle pollen between male and female plants.

The process unfolds in stages. Male cycads first warm their pollen-producing cones, drawing beetles in to feed. Later, female plants heat their ovulate cones, luring the insects away and ensuring that pollen is transferred to fertilize developing seeds. According to the researchers, this use of infrared radiation represents one of the oldest known pollination signals, predating the vivid colors that dominate modern flowering plants.

“This is basically adding a new dimension of information that plants and animals are using to communicate that we didn’t know much about before,” said Valencia-Montoya, currently a junior fellow in the Harvard Society of Fellows.

The research focused on Zamia furfuracea, a small cycad native to Mexico commonly known as the cardboard palm, and its exclusive pollinator, a long-snouted brown weevil. Thermal imaging revealed that heat production is concentrated in the reproductive cones, where tissues are packed with energy-producing mitochondria. In this species, cones can warm to as much as 46 degrees Fahrenheit above the surrounding air temperature.

Across 17 cycad species, the scientists found a consistent daily rhythm: male cones heated at dusk, followed by female cones warming several hours later. Field experiments showed that beetles moved in lockstep with these temperature shifts.

Further investigation revealed how the insects perceive the signal. Using microscopy and physiological tests, the team identified specialized heat-sensing organs in the beetles’ antennae, including a molecular sensor known as TRPA1.

The findings suggest that heat-based signaling was integral to early pollination systems, long before flowers relied on color. The researchers say the signal’s long invisibility to science likely reflects human sensory limits. As Valencia-Montoya noted, “The ones that are hidden are just as important.”

The study was co-authored with Valencia-Montoya's former advisor, Naomi Pierce, and Nicholas Bellano in the Department of MCB.  The research was funded in part by the National Institutes of Health.