Monday, 22 March 2010

Flowers Bloomed Before Modern Insects Buzzed



The latest estimation of when flowering plants first appeared on Earth has moved back to 215 million years ago. This is up to 75 millions years earlier than thought previously and places the first flower before the evolution of modern insects like bees and wasps.

Stephen Smith from the National Evolutionary Synthesis Center, and Jeremy Beaulieu and Michael Donoghue both from Yale University, have just published a paper in Proceedings of the National Academy of Sciences. They use molecular sequencing to show that the flowering plant branch of the 'tree of life' is older than we thought.

From what we see in fossils, it appears that bees, flies and wasps that feed on nectar and pollen evolved first, with flowers coming later, perhaps around 140 million years ago. That is, the insects must have got their food from elsewhere before flowering plants came along. This new finding brings these insects and flowering plants closer together, suggesting a more intimate co-evolution may have been at work in the early years of both groups.

The story might go something like this. A plant produces nectar to get rid of some waste product and this becomes a food source for particular insects. The nectar might come from the stem at first but sometimes close to a flower. If more is produced near the flower there is more chance a visiting insect will also carry pollen from one plant to another - leading to more successful reproduction.

Plants producing nectar near or in flowers produce more offspring. Insects that find this nectar produce more insect offspring. The two organisms could then evolve together so that the insect gets a steadier food source and the plant a more regular pollinator. Or it could be far more complicated...

The 'first flower' is a topic I've blogged on a few times. Until now the dating had relied on fossils. As the authors of the paper note, it's possible flowering plants may not have been very abundant at first, leaving little imprint in the fossil record. In this scenario, their appearance in the fossil record would represent an explosion of species.

However under this model the authors quite correctly add that it would be unlikely for early flowering plants to have such a major impact on the evolution of insects. They admit that the molecular dating may be wrong - the methods are notoriously open to interpretation - so there is some more checking to do.

Alternatively, a earlier fossil may turn up that proves the 'long fuse burning and then KABOOM!' model, as Donoghue describes it. Donoghue is also quoted in the media release as saying '...the gap [between the first flower appearing in the fossil record and the date implied by molecular data] is getting wider... And in the end, that might actually be interesting".

Which is what science is all about, following up interesting leads.

Image: Some flowers from a garden in the Southern Highlands - what the insects had in store for them after the KABOOM.

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