Ancient Cycads Deployed Infrared Heat Signaling to Guide Insect Pollinators

A groundbreaking study published in the journal Science in 2025 has unveiled that ancient cycads utilized thermal, or infrared, signaling as a method to attract their pollinators. Scientists estimate this sophisticated strategy originated approximately 275 million years ago. This approach predates the evolution of flowering plants and their reliance on visual cues by millions of years, positioning thermal emission as one of the earliest forms of communication language within the plant kingdom.

The research, spearheaded by Wendy Valencia-Montoya of Harvard University, provided concrete evidence demonstrating that the reproductive structures of cycads, specifically the cones of the species Zamia furfuracea, actively generate heat. Experimental data, captured through thermal imaging, revealed that the male cones possess the capability to elevate their temperature by as much as 15 degrees Celsius above the ambient surroundings. This metabolic intensity is comparable to the energy expenditure observed in hummingbirds. This process of thermogenesis adheres strictly to a circadian rhythm: the male cones warm up as evening approaches, and roughly three hours later, the female structures follow suit, ensuring a sequential transfer of pollen.

Cycads achieve this elevated thermal state by metabolizing stored starch within their mitochondria, a highly energy-intensive undertaking. The moderate heating of the male cones functions as an initial 'come hither' signal. Conversely, an excessive temperature rise appears to prompt the insects to move toward the female reproductive organs. This push-and-pull mechanism, which integrates heat, scent, and humidity, effectively directs the beetles away from the pollen-bearing male cones and toward the female structures necessary for fertilization.

A crucial component of this long-standing symbiotic relationship lies in the specialized adaptations found in the pollinating beetles, particularly the weevil species Rhopalotria furfuracea. The investigators determined that the antennae of these insects are equipped with specialized thermoreceptors containing the TRPA1 protein. This protein grants the beetles the ability to precisely detect infrared radiation, even when light levels are low, which is vital for their crepuscular pollination activities. When researchers blocked this specific receptor, the beetles became completely unresponsive to the thermal cues. Furthermore, scentless 3D models of the cones that were artificially heated successfully lured the insects without fail.

Cycads first appeared around 275 million years ago and reached their peak diversity during the Jurassic period. Today, however, they face significant threats as flowering plants, which rely on visual signals, dominate the landscape. According to the lead author, this discovery unlocks a 'new dimension of information' that had previously gone unnoticed due to inherent human sensory bias. The heat-based interaction between cycads and their associated beetles represents one of the most ancient examples of co-evolution documented on Earth.