Thomas' Plant-Related Blog

On plant science. Mostly.

Insect pollination long before flowering plants

with 7 comments

ResearchBlogging.org

The first flowering plants evolved more than a hundred million years ago, while dinosaurs were still on the scene. Since then, they’ve come to dominate the world, largely outcompeting the plants that were there before, such as conifers, cycads, and ginkgoes. With some exceptions (particularly the taiga, the coniferous forests of Russia and Canada), the vast majority of the vegetation we now see are flowering plants, or angiosperms. That includes things that don’t obviously flower, like grass and oak trees.

There are a few different ideas as to why the new flowering plants did so well. Some modern ones focus on differences in the plants’ water transport: the slow seedling hypothesis says that baby angiosperms can get off to a sprint start, overshadowing competitors before they’d left the starting blocks. Making your food from sunlight might sound like an easy life, but plants have to fight for daylight, and getting on top can be the knock out blow.

Older theories tended to be more focussed on reproduction. It’s not simply a flower that officially distinguishes a flowering plant; unlike other plants, the unfertilised egg is completely enclosed, and the pollen (containing the male sex cells) has to drive a pollen tube through part of the parent plant. Their other name, angiosperms, comes from Greek words for ‘vessel’ and ‘seed’.

Pine pollen on water

Pines produce lots of pollen—inefficient, but it makes some nice abstract patterns on water. Image by finna dat on flickr (link on image).

Flowers are, however, important. The reason for showy flowers is to attract pollinators, most commonly insects. Today, the majority of flowering plants use insects to carry their pollen, whereas most gymnosperms (the older group of plants, including conifers) are pollinated by the wind. Insects have one clear advantage over the wind: they can track down another flower of the same species, so you don’t have to produce huge amounts of pollen. This was the basis for one theory about the rise of angiosperms: they simply did pollination more efficiently.

The new work throws up a big problem with that idea. From insect fossils, it looks like there were pollinators around in the Jurassic, which had evolved together with the gymnosperms that were around at the time. If angiosperms had tried to patent working with insects to transfer pollen, there would have been prior art.

To be precise, the scientists describe several species of scorpionfly, whose mouthparts look like they evolved to suck up some sort of fluid (but blood didn’t seem to have been on their menu). And the relationships of these groups suggest that the same way of feeding evolved several times. This would all fit in with some fossil gymnosperms, which don’t seem to have been terribly well adapted for wind pollination.

As the perspective (second reference below) puts it, however: “a key piece of evidence is missing: The authors failed to find any pollen associated with these fossils.” Pollen still stuck to fossilised insects would really clinch the deal, and is worth hoping for. But if you accept that insect pollination was going on, there are other groups of insects that could also have been involved, and the story’s certainly not far fetched.

Finally, I wonder if it was really gymnosperms which those Jurassic scorpionflies were pollinating. It’s not clear just when the first flowering plants did arise, but it has been suggested that their separate lineage goes back that far. The authors argue that, because several groups of insect evolved the same feature, they must have been using a widespread group of plants, which might rule out the ancestors of today’s flowering plants.

References

Ren, D., Labandeira, C., Santiago-Blay, J., Rasnitsyn, A., Shih, C., Bashkuev, A., Logan, M., Hotton, C., & Dilcher, D. (2009). A Probable Pollination Mode Before Angiosperms: Eurasian, Long-Proboscid Scorpionflies Science, 326 (5954), 840-847 DOI: 10.1126/science.1178338 (Technical)
Ollerton, J., & Coulthard, E. (2009). Evolution of Animal Pollination Science, 326 (5954), 808-809 DOI: 10.1126/science.1181154 (More readable)

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Written by Thomas Kluyver

10 November, 2009 at 12:09 am

Posted in Papers

7 Responses

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  1. Fascinating work and hypothesis! Is it known which species descended from these scorpionflies? In other words, can we track back nectar feeding ability to these species?

    lucas

    10 November, 2009 at 11:04 am

    • Hi Lucas,

      They’re from three extinct families, so I guess they left no direct descendants. There are still scorpionflies around (the order Mecoptera), and Wikipedia reckons, with citations, that the evolutionary group might also include fleas, moths & butterflies, and true flies.

      As for tracking nectar feeding ability, I think its arisen several times independently. Interestingly, the major pollinators are quite closely related: http://www.tolweb.org/Endopterygota/8243
      But on the other hand, ‘major pollinators’ mostly comprises just two groups (bees, and moths/butterflies), so it could just be co-incidence.

      Thomas Kluyver

      10 November, 2009 at 11:33 am

  2. Its really intersting and i will be grateful to u if u send me some more information related to this matter.

    Reshmi Chatterjee

    2 September, 2010 at 3:56 pm

    • What do you want to know about?

      Thomas Kluyver

      3 September, 2010 at 12:06 am

  3. what is the advantage of insect pollination over wind pollination

    Beatriz Torrefranca

    3 January, 2016 at 3:23 am

    • I’d guess that it’s more efficient – when pollen is released into the wind, only a tiny fraction of it will reach the right part of the right species of plant, while most of it is wasted. There’s a good chance that an insect that visits one flower will visit others of the same species and transfer pollen to them. So an insect pollinated plant can produce much less pollen and still have a good chance of passing on its genes.

      There are probably advantages to wind pollination too, though. As any hayfever sufferer knows, there are still plenty of wind-pollinated species around, including grasses and many trees.

      Thomas Kluyver

      4 January, 2016 at 11:22 am

  4. […] Eating voraciously, they facilitate the grand romance of flowering plants or angiosperms. Angiosperms made a major breakthrough about 100 million years ago. The breakthrough using pollinators to fertilize eggs in one plant with sperm in another. link […]


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