Heat generated by plants: a key factor in the evolutionary history of pollination?

To what extent has the ability of some plants to generate a significant amount of heat played a crucial role in the evolutionary history of pollination? A new study has sought to answer that question.

Although thermogenesis, a process by which organisms generate heat internally and which occurs in some plants, cannot be directly preserved in the fossil record, scientists can infer its presence in ancient plants by studying similar anatomical structures today.

A new study led by the Botanical Institute of Barcelona (IBB), a joint centre of the Spanish National Research Council (CSIC) and the Barcelona Natural Sciences Museum Consortium (CMCNB), has examined the characteristics of current thermogenic plants, those that have the capacity to produce their own heat from internal metabolic processes, and has compared them with the characteristics that can be deduced from various lineages of fossil plants.

The work has been carried out in collaboration with several institutions, including the University of Barcelona (UB), the Complutense University of Madrid (UCM) in Spain, the Geological and Mining Institute of Spain (IGME, part of the CSIC), the Smithsonian Institution in the United States, and the Sydney Botanic Gardens in Australia.

Thermogenesis is often associated with animals, but some plants have also evolved this ability. This metabolic process allows certain parts of the plant, such as flowers and inflorescences (clumps of flowers), to raise their temperature above that of the environment. The heat they generate helps volatilize and disperse floral fragrances and other chemical compounds that attract insects such as beetles, flies, and others to the plants, facilitating their pollination. In addition, thermogenesis stabilizes the development of reproductive organs in cold climates and facilitates the growth of pollen tubes.

“Our findings suggest that thermogenesis in plants is an older phenomenon than previously thought,” explains David Peris, a researcher at IBB and first author of the study. “200 million years ago, the diversification of angiosperms, flowering plants, had not yet occurred. Therefore, thermogenesis could have been a crucial factor in the evolutionary success of seed plants in general, and flowering plants in particular, and also of their pollinators.”

Bee, a typical pollinating insect. (Photo: NPS/Christina Martin)

A discovery with evolutionary implications

In thermogenic plants, the female structures mature before the male ones to avoid self-fertilization. This feature is identified in the most primitive extant groups of angiosperms, where the stamens and carpels (the male and female reproductive parts respectively) were enclosed separately in small chambers. Furthermore, the fact that some fossil plants had reproductive chambers that could have trapped pollinating insects suggests that this feature already existed in plants before the appearance of flowers.

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

According to the authors of the research, the ability to generate heat may have given certain Mesozoic plants, more than 200 million years ago, a competitive advantage over non-thermogenic plants, by attracting pollinating insects more efficiently, thus contributing to their reproductive success. This strategy of attracting pollinators may have preceded others, such as the striking colours of flowers, and may have been influenced by global climate changes in the past. In addition, thermogenesis is closely linked to the emission of fragrances, another crucial factor in attracting insects.

This study opens new avenues to explore how these interactions influenced the diversification of plants and their pollinators throughout evolutionary history. “Thermogenesis in plants is not just a botanical curiosity,” says Iván Pérez-Lorenzo, a researcher at the IBB and also a participant in the study, “but it is an important factor that has contributed to the success of the two most diverse groups of organisms today: insects and angiosperms, and has key implications for understanding the evolution of pollination strategies.”

The study is titled “The impact of thermogenesis on the origin of insect pollination”. It has been published in the academic journal Nature Plants. (Source: IBB / CSIC)