Plant thermogenesis has played a key role in attracting pollinating insects for at least 200 million years, study finds

Thermogenesis is a process by which organisms generate internal heat. Although it is usually associated with animals, some plants have also evolved this ability. This metabolic process allows certain parts of the plant, such as flowers and inflorescences, to raise their temperature above that of the surrounding environment.

Today, these plants, which include cycads and some angiosperms (flowering plants), rely on insects for pollination. The heat they generate helps volatilize and disperse floral scents and other chemicals that attract insects such as beetles, flies, and trebuchets to the plants. In addition, thermogenesis stabilizes the development of reproductive organs in cold climates and facilitates the growth of pollen tubes.

Evidence in the fossil record

Although thermogenesis cannot be directly preserved in the fossil record, scientists can infer its presence in ancient plants by studying anatomical structures similar to those in present-day thermogenic plants.

A new study led by the Barcelona Botanical Institute (IBB), a joint centre of the Spanish National Research Council (CSIC) and the Consorci Museu Ciències Naturals de Barcelona, ​​in collaboration with the Complutense University of Madrid and other institutions such as the Geological and Mining Institute of Spain (IGME-CSIC), the Smithsonian Institution, the University of Barcelona and the Royal Botanic Gardens in Sydney, has examined the characteristics of current thermogenic plants and compared them to fossil plant lineages.

The work appears in Nature Plants.

“Our results suggest that thermogenesis in plants is an older phenomenon than previously thought,” says David Peris, a researcher at IBB and lead author of the study. “Two hundred million years ago, the diversification of flowering plants had not yet occurred. Therefore, thermogenesis may have been a crucial factor in the evolutionary success of seed plants in general, and flowering plants in particular, as well as their pollinators.”

A discovery with evolutionary implications

In thermogenic plants, female structures mature before male structures to avoid self-fertilization. This is related to the early diverging lineages of angiosperms, which had floral chambers where stamens and carpels closed independently. The presence of reproductive chambers in fossil plants that could have trapped pollinating insects also suggests that this feature existed in the past.

Large reproductive structures, such as perianths or cones, could also indicate thermogenesis, as they retain heat more efficiently. This study allowed scientists to identify fossil plant lineages that may have exhibited thermogenic activity, suggesting that thermogenesis has been present in seed plants for longer than previously thought.

The ability to generate heat may have given some Mesozoic plants, more than 200 million years ago, a competitive advantage over non-thermogenic plants by more effectively attracting pollinating insects, thereby contributing to their reproductive success. This strategy for attracting pollinators may have preceded other strategies, such as bright flower colors, and may have been influenced by past climate changes. In addition, thermogenesis is closely linked to scent emission, another crucial factor in attracting insects.

This study opens new avenues to explore how these interactions have influenced the diversification of plants and their pollinators throughout evolutionary history.

“Plant thermogenesis is not just a botanical curiosity,” says Iván Pérez-Lorenzo, a researcher at IBB and participant in the study. “It is an important factor that has contributed to the success of the two most diverse groups of organisms today: insects and angiosperms, and it has key implications for understanding the evolution of pollination strategies.”