Flowering plants have long been known for their intricate relationship with pollinators like insects, birds, and mammals. These interactions are central to the reproduction of most angiosperms, or flowering plants, with pollination often involving specialized mechanisms that ensure the transfer of pollen between plants. However, before flowering plants evolved and took over the Earth’s ecosystems, an entirely different group of plants—the cycads—may have had a similar relationship with insects. Recent research has uncovered some remarkable fossil evidence that provides new insights into the ancient pollination strategies of cycads, suggesting that they might have been among the first plants to rely on insect pollinators.
In a study published on August 16 in Current Biology, a team of researchers uncovered fossilized evidence from approximately 99 million years ago in Burmese amber. This discovery revealed an ancient boganiid beetle preserved alongside cycad pollen, marking one of the earliest, most definitive instances of insect pollination in the plant kingdom. The findings offer a rare glimpse into the ancient ecological relationship between cycads and the insects that helped them reproduce during a time long before the dominance of flowering plants.
Cycads, an ancient group of gymnosperms (non-flowering seed plants), have been around for over 300 million years, thriving during the age of dinosaurs. Unlike flowering plants, cycads have cones instead of flowers and rely on wind or animals to transport their pollen. While cycads have been known to interact with pollinators, definitive evidence linking these plants to insect pollination was scarce until this discovery. The recent find suggests that cycads may have been the first plants to develop a specialized relationship with insects for pollination, and this interaction might have begun as early as the Jurassic period, well before the rise of angiosperms in the Cretaceous.
The beetle found preserved in amber belonged to the boganiid family, which today includes beetles that are known to pollinate cycads. These modern beetles, particularly the Australian Paracucujus, are still vital pollinators for a species of cycad called Macrozamia riedlei. The ancient beetle, however, had features that strongly suggest it was a pollinator of cycads as well. Its large mandibles, which are lined with bristly cavities, seemed perfectly adapted for carrying pollen. This was a key observation that caught the attention of Chenyang Cai, a research fellow at the University of Bristol and the lead author of the study.
Upon examining the fossil under a microscope, Cai was able to identify multiple clumps of cycad pollen attached to the beetle’s mandibles. These pollen grains were confirmed to belong to cycads by Liqin Li, an expert in ancient pollen at the Chinese Academy of Sciences. This was an important breakthrough, as it provided solid evidence that this beetle was not just an herbivore or scavenger but was, in fact, engaged in the pollination of cycads. The presence of cycad pollen on the beetle was further confirmed by extensive analysis, which supported the hypothesis that these beetles played an essential role in the reproductive process of cycads, acting as vectors to transfer pollen from one plant to another.
To better understand the evolutionary relationship between this ancient beetle and modern beetles that pollinate cycads, the researchers conducted a detailed phylogenetic analysis. This analysis revealed that the beetle trapped in amber belonged to a sister group to the extant Paracucujus beetles. Modern Paracucujus beetles are known to pollinate certain cycad species in Australia, such as Macrozamia riedlei. This connection between the ancient beetle and modern pollinators strongly supports the idea that the mutualistic relationship between cycads and beetles dates back to at least the Early Jurassic, suggesting that cycads and beetles co-evolved over millions of years.
This discovery has profound implications for our understanding of plant-pollinator relationships in ancient ecosystems. It highlights the role of insects in pollinating plants long before the rise of flowering plants and their specialized pollinators, such as bees. In particular, the study suggests that cycads were at the forefront of developing insect-pollinator partnerships during a time when the Earth’s flora was dominated by gymnosperms. Beetles likely played a crucial role in the evolution of cycads, facilitating their reproduction and ensuring their persistence for millions of years.
The findings also shed light on the distribution patterns of modern boganiid beetles and their cycad hosts. Today, boganiid beetles are found in regions such as South Africa and Australia, where they pollinate certain species of cycads. The discovery of similar beetles in ancient amber supports the idea that this pollinator-plant relationship has existed for tens of millions of years and may have contributed to the spread of cycads across various continents. It also suggests that cycads once had a much broader geographical range than they do today, although their distribution has since been limited to specific tropical and subtropical regions.
One of the challenges researchers face in studying ancient insect-pollinator relationships is the preservation of fossils. Unlike larger animals, which are often preserved in bones or shells, insects are small and delicate, making fossilization a rare occurrence. Furthermore, older Jurassic-era beetles are typically found as compression fossils, where the original body is flattened and lacks the detail that can be seen in specimens preserved in amber. This makes the discovery of the boganiid beetle in amber particularly significant, as it offers a rare and detailed look at the anatomy of ancient pollinators.
Chenyang Cai and his colleagues have been searching for similar beetle fossils for the last five years, hoping to find more evidence of ancient insect-pollinator relationships. The challenge, however, is that most Jurassic beetles are not preserved in amber, which makes it difficult to find such well-preserved specimens. Nevertheless, Cai’s findings open up new possibilities for studying the evolution of pollination, especially in ancient plants like cycads. The study of these ancient relationships is not only important for understanding the history of plant reproduction but also for shedding light on the broader ecological dynamics of prehistoric ecosystems.
Cycads, though now largely overshadowed by flowering plants, remain a fascinating and important part of Earth’s botanical history. They are considered “living fossils” because they have changed very little over millions of years. Understanding their interactions with ancient pollinators like beetles provides valuable insight into the evolutionary history of plant-pollinator relationships and the complex web of life that existed long before the rise of angiosperms. By examining the fossils preserved in amber, researchers are able to piece together the ecological history of the Earth and understand how plants and animals co-evolved to shape the world we live in today.
More information: Current Biology, Cai et al.: “Beetle Pollination of Cycads in the Mesozoic” www.cell.com/current-biology/f … 0960-9822(18)30827-3 , DOI: 10.1016/j.cub.2018.06.036