Can in-situ pollen link fossil plants to floral visitors?

Flowering plants and insects are the most diversified and widespread groups of plants and animals on earth. The parallel diversification of flowering plants and various flower visiting/feeding insect lineages, including beetles, bees, butterflies, moths, and flies, suggests a mutualistic interaction between flowering plants and their major pollinators. Flowering plant interaction with pollinators seems also to be the driver behind specialization and subsequent diversification in both plants and insects. To test hypotheses regarding evolutionary dynamics of flowers and their insect visitors, the examination of the fossil record of flower-insect interactions is essential. To investigate the Paleogene co-evolution between insects and flowering plants in- situ pollen from the anthers of fossil flowers and from the exterior or internal organs of fossil insects will be studied. This project will be the first test whether in-situ fossil pollen can link insects and flowers from the same fossil assemblage. It will be the first study to include a large number of different insects and flowers from the same fossil assemblage, and from different periods of the Paleogene. In addition, it will provide large-scale direct evidence for flower-insect interaction during the time of major radiations of both insect pollinators and flowering plants, adding crucial information to the evolutionary history of interactions between flowers and their insect visitors. Finally, fossil pollen from three sources of the same assemblages will be investigated; i.e. dispersed pollen from sedimentary rock samples, in-situ pollen from fossil flowers, and pollen from the exterior or internal organs of fossil insects. This will for the first time show how representative dispersed palynofloras are of the "actual" paleovegetation.

Flowering plants and insects form one of the most important partnerships in nature. Today, nearly 90% of flowering plants depend on animal pollinators, mainly insects, to reproduce. These interactions are essential for maintaining biodiversity and ecosystem stability. However, understanding how such relationships developed over millions of years remains difficult, because direct fossil evidence is extremely rare. The project "Flower Power: can in-situ pollen link fossil plants to floral visitors?" set out to uncover these ancient interactions by studying fossil pollen preserved directly on insects and within fossil flowers. Pollen grains are highly distinctive and can often be linked to specific plant groups. When found attached to fossil insects, they provide rare, direct evidence of which plants these insects visited. The research focused on exceptionally well-preserved fossil sites in Europe, dating from approximately 66 to 23 million years ago. These ancient lake deposits contain fossils of insects, flowers, and pollen in remarkable detail. Using a combination of light microscopy and advanced electron microscopy, individual pollen grains were carefully extracted and analysed, allowing precise identification and comparison with modern plants. The project revealed that early pollination systems were already complex. Fossil bees were found carrying pollen from multiple plant groups, showing that they acted as important and flexible pollinators early in their evolutionary history. In one case, an early large carpenter bee was preserved with pollen from two different plant families, providing direct evidence of its foraging behaviour. These findings demonstrate that diverse plant-insect interactions were already established tens of millions of years ago. At the same time, the results show that pollination systems have changed over time. A fossil flower of the genus Ludwigia was found associated with beetles carrying its pollen, indicating that beetles likely played a key role as pollinators in the past. Today, however, Ludwigia species are mainly pollinated by bees. This suggests that pollination strategies can shift significantly over evolutionary time. Overall, the project delivers rare, direct evidence of how plants and insects, especially bees, interacted in the distant past. These findings improve our understanding of the evolution of pollination and the development of complex ecosystems. They also provide an important foundation for future research on biodiversity and how ecological relationships respond to environmental change over long timescales.