The relationship between insects and flowering plants might be the greatest symbiotic success story on Earth, allowing both to flourish to an extraordinary degree. Some biologists have started to suspect, however, that insect pollination preceded the rise of the angiosperms, or flowering plants. Now a single beetle trapped in amber has convinced them.
Animal pollination of plants addresses the central problem of each kingdom. Animals can’t produce their own food, and directly or indirectly need photosynthesizers to do that for them. Plants can’t move, so if they are to mate with others at a distance they need assistance, and the wind is an unreliable disperser of seed.
By each giving the other what they needed most, angiosperms and insects achieved dominance so great we take it for granted. However, Dr Chenyang Cai of the Chinese Academy of Sciences and the University of Bristol has shown they did not invent the idea.
Some plants like ferns do without seeds entirely, but even among the spermatophytes – plants that produce seeds – flowers are not universal. Cycads like conifers are classified as gymnosperms, meaning naked seeds, and lack the attractive packages in which flowering plants wrap their seeds.
Where other gymnosperms are wind-pollinated, cycads are fertilized by beetles. Although 330 species survive, they are outnumbered by flowering plants almost 1,000 to 1. During the age of the dinosaurs, it was a different matter. The fossil record shows cycads made up much of the world’s forests until developments in the mid-Cretaceous gave angiosperms important advantages, resulting in a swift rise to dominance.
Around 99 million years ago, right about the time cycads were being displaced, a boganiid beetle became trapped in amber in what is now Myanmar. When shown this specimen, Cai noticed its large mandibles, resembling those used to pollinate cycads today.
Closer examination revealed the beetle, now named Cretoparacucujus cycadophilus, carried tiny pollen grains, which were confirmed as being from a cycad.
The beetle in question has a living relative, Cai reports in Current Biology, the Australian Paracucujus, a specialist pollinator of the cycad Macrozamia riedlei. The fact that Cretoparacucujus was in Asia suggests the lineage predates the break-up of Pangea.
Cai’s beetle itself probably postdates the flowering plant/insect alliance. However, if its divergence from Paracucujus is as long ago as suspected, the family has likely been carrying cycad seeds around for many millions of years, probably back to at least the early Jurassic.
The timing of the angiosperms’ origins is still debated, but likely happened after the first beetles and cycads formed their symbiotic relationship. Thus, it seems the cycads were the originators, and indeed may have created a pool of insects sufficiently adaptable to become the angiosperms' pollinators, setting the stage for the wealth of richness and beauty flowers bring into the world.