Thermogenesis is a process by which organisms generate internal heat. While it is commonly associated with animals, some plants have also developed this ability. This ability to produce heat allows certain parts of plants, like flowers and inflorescences, to raise their temperature above the surrounding environment. Though rare among plants, this process plays a vital role in plant reproduction and survival, particularly in attracting pollinators and ensuring the proper development of reproductive structures.
Plants that rely on thermogenesis today include cycads and some angiosperms (flowering plants). These plants utilize the heat they generate to volatilize and disperse floral fragrances, which attract pollinating insects such as beetles, flies, and thrips. Additionally, thermogenesis helps plants in cold environments by stabilizing the development of reproductive organs and promoting the growth of pollen tubes. This ensures that reproduction can take place even in cooler climates, making thermogenesis an important adaptation for survival.
Although thermogenesis cannot be directly observed in the fossil record, scientists have inferred its presence in ancient plants by examining their anatomical structures. By studying modern thermogenic plants and comparing them with fossilized plant lineages, researchers have identified similarities that suggest thermogenesis existed in ancient plants. A new study conducted by the Botanical Institute of Barcelona (IBB), in collaboration with institutions like the Complutense University of Madrid and the Smithsonian Institution, supports this theory.
According to the study, thermogenesis in plants may have been a far older phenomenon than previously thought. Researchers believe that the process could have been crucial in the evolutionary success of seed plants and, later, flowering plants. Two hundred million years ago, flowering plants had not yet diversified, but thermogenesis might have played a pivotal role in attracting pollinators and ensuring the survival of these early seed plants. The ability to generate heat would have given thermogenic plants an edge over their non-thermogenic counterparts by enabling them to attract pollinators more effectively.
In thermogenic plants, female reproductive structures often mature before male structures, a process that helps to avoid self-fertilization. Fossil evidence suggests that early angiosperms (flowering plants) had floral chambers where male and female structures matured separately, much like modern thermogenic plants. These reproductive chambers likely trapped pollinators, indicating that thermogenesis could have existed long before the evolution of modern plant species.
The presence of large reproductive structures, such as cones or perianths, in fossilized plants also hints at thermogenesis, as these structures are effective at retaining heat. The study has identified several ancient plant lineages that may have exhibited thermogenic activity, suggesting that this phenomenon has been present in plants for over 200 million years.
Thermogenesis likely gave Mesozoic-era plants a significant evolutionary advantage by helping them attract insect pollinators. This advantage would have contributed to their reproductive success and helped them compete with other non-thermogenic plants. The process of attracting pollinators through heat generation could have preceded other strategies, such as the evolution of bright flower colors, and may have been influenced by changes in climate.
Thermogenesis is also closely linked to the emission of fragrances, another essential factor in pollinator attraction. The heat generated by plants helps release chemical compounds that attract insects, facilitating pollination. This combination of heat and fragrance emission may have been a key factor in the co-evolution of plants and their pollinators over millions of years.
The findings of this study have far-reaching evolutionary implications. Thermogenesis is not just a curious trait of a few plant species but a critical factor in the survival and success of both plants and insects. By attracting pollinators more efficiently, thermogenic plants helped shape the evolutionary landscape of both plant and insect diversity. Today, insects and angiosperms are among the most diverse groups of organisms on Earth, and their evolutionary success may be closely tied to the ancient development of thermogenesis in plants.
This discovery offers a new perspective on the evolution of pollination strategies and highlights the complex interactions between plants and their pollinators throughout history. As researchers continue to study the fossil record and modern plant species, they may uncover even more about how thermogenesis influenced the development of life on Earth.
The study is published in Nature Plants.