Pretty Petals to Pull in Pollinators
Chris - We'd better pick up our first passenger and that is Beverley Glover from Plant Sciences. Welcome.
Beverley - Hi, Chris.
Chris - I know I promised you a ride down the river Cam, a boat ride or a cruise or something and this is the best we can do. It's a low budget show!
Beverley - It's alright. We're quite used to it in Cambridge!
Chris - Now you're from Plant Sciences. What are you devoting most of your time to at the moment?
Beverley - Most of our work at the moment is about the surface of the flower, particularly the surface of the petals, and how different structures affect the way that the animals interact and collect its pollen and pollinate it.
Chris - How do flowers actually work?
Beverley - A flower is basically a bright advertising thing that says to animals there's something good to eat over here. The animal comes along looking for the reward, a good thing to eat, which is usually nectar and in doing so picks up a bit of the plant's pollen. It transfers it then to another flower and that way the plant gets fertilised and makes the seed.
Chris - What about the way the flower mechanically works? If you zoom in with a microscope and look at it in more detail what's actually there?
Beverley - Different flowers have different surface structures depending on what they're trying to attract. Different animals have different preferences. One thing we've looked at is if cell structures give grip so that if they're trying to land in high wind or at difficult angles they have something to get a grip on. Another thing we've been looking at is much smaller surface structures on a nanometre scale which affect the light that's being refracted and can give you iridescence on the flower.
|Mimulus flower photographed in visible light (left) and ultraviolet light (right) showing a nectar guide visible to bees but not to humans. © Plantsurfer @ wikipedia|
Chris - So this will presumably mean that different animals or different insects can differentially see the flower and therefore it's more attractive to certain species than others.
Beverley - Yes, exactly. One thing that plants can do with structure is make sure they reflect very highly in the ultraviolet end of the spectrum which we can't see but many insects can. That makes the flower look much brighter to an insect than it is to us and makes it very attractive to them.
Chris - Why do insects want to see the UV? Where do they get that trait from?
Beverley - Not all insects have the same colour vision but bees which is what we mostly work with have three photoreceptors like we do but whereas we see the primary colours they see the ultraviolet, blue and green. The world looks very different to them and the flowers are adapted to how they want to look, not how we want them to look.
Chris - Is it anything to do with the fact that on a cloudy day UV can still come through and other wavelengths might not?
Beverley - It may well be. There is quite a lot of evidence that pollinator colour vision, or bee colour vision at least, evolved before flowers. It's as if the flowers have had to suit their colours to what the animals already had. It's not the other way around, the animals weren't going, "the flowers are red so I need to see red." That worked for them and then the flowers have adapted to suit.
Chris - Why would they need colour vision if there was no flower around to pollinate?
Beverley - That's a good question. One possibility was for the animals to see one another. A lot of insects are shiny in the ultraviolet or iridescent and that helps them attract mates or identify enemies and so on. Colour vision's important for seeing one another too.
Chris - Going back to the petals for a second. Those cells you're looking at to give grip - is that just all they do, they're sort of sticky to certain insects or do they have other jobs?
Beverley - No that's not all they do. I wish it was that simple. They also change the way the flower looks because they act as little lenses that focus the light on the flower to make it look brighter so we can see that effect. Animals can see it to; insects can see it too but it may not be very important to them. They can see it but they don't really care. They may also make the flower warmer by trapping heat. When they trap light they trap energy and so they make the flower slightly warmer. That to some pollinators in some environments maybe the most significant factor of the flower. It means that you don't have to spend as much energy warming yourself up to be able to fly.
Chris - You had a paper in Nature exploring that a couple of years ago.
Beverley - Yes, that's right. We showed that even a perfectly normal bumble bee at ambient temperature would prefer a warmer flower to a cooler one given the choice if the reward's the same in both. I think the difference these cells can make to how warm the flower is isn't very great for a flower on a sunny day or normal habitat. To pollinators that are foraging perhaps at dawn when the flowers are still quite cold, they might make enough of a difference to be significant.
Chris - Why does it make a difference? Why does an insect want to drink warm nectar?
Beverley - because it doesn't have to spend any energy warming it up itself. Bess have to spend some energy warming their bodies up just to be able to fly. It's like you having a hot drink. If the nectar comes in warmer then you don't have to spend as much energy warming it up.
Chris - Do all plants have these cells or is it just the preserve of ones that want to specifically attract certain insects?
Beverley - About 80% of plants have these flowering cells. We think that some are doing it for tactile reasons to give the animal a grip, some are doing it for other reasons. Some might be doing it for the effect it has on the flower looks. It seems to be an ancestral trait. Flowers seem to have had it from when they were first flowers. The plants that don't have it seem to have lost it That's actually something we're quite interested in is exploring those plants and why they've lost something that seems to be so useful.
Chris - Plants that don't rely on insects to get pollinated, do they not have them?
Beverley - Most wind-pollinated plants have lost petals entirely so they don't have these structures which are only on the petals.
Chris - Looking beyond that where do you think this is going to go next? There must presumably be mutant flowers that don't have these cells and are they less fit? Do they grow less well?
Beverley - Yes. We have a mutant line of snap dragon (Antirrhinum majus) and also a mutant line of petunia that don't make these cells. I think they're perfectly fit and grow perfectly well in the greenhouse. If we plant them out we find they don't set as much seed. They don't get pollinated as well. They're not as attractive to bees. Those mutants have let us identify the genes that control this process. We can start to understand in the plants that have 'deliberately' lost them, the flowers that never have them, what's happened to those genes - where they've gone and why they're not working any more.
Chris - So does this mean that if gave the plants more of these genes or made them express more of these cells you could make them more fertile, more fit and you'd get better yields off them?
Beverley - It would depend on the plant but that's certainly something we're thinking about. For instance, a lot of the members of the tomato family have lost these cells because of the way the flower is pollinated. The animals hat are attracted to them don't need them either for grip of for vision. The tomato itself hasn't lost them so one other thing we're interested at the moment is if we knock those genes out of tomato can we make it more attractive to pollinators to sew more fruit.
Chris - They're buzz pollinators, aren't they? In Australia they have to import bumble bees that can buzz at the right frequencies to make the pollen come out.
Beverley - Exactly. They're attracted to the anther which is the bright yellow thing that produces the pollen. That's what they're trying to collect to feed to their larvae, not the nectar out of the petals. The petals have become irrelevant and so we think for most buzz-pollinated species these cells have been lost because you're not trying to make the petals stand out. Tomato for some reason hasn't lost them so that's something we'd like to explore.
Chris - And just lastly, with a name like Beverley Glover working on Plant Sciences have you never been tempted to add the word fox in the middle so you could be a plant scientist called Beverley Fox Glover?
Beverley - You know it's funny. My husband makes that joke all the time!