Flowers change their shape to attract insects
35% of our food comes directly from plants that need pollinating, so it really is in our best interests to understand the relationships between plants and their pollinators. And a new study has made a fascinating discovery that some flowering plants can alter the chemistry of their petals to change the shape of their cuticle - that’s the plant outer “skin” - and this produces crinkled formations, called striations, on the flower surfaces. The result is a more jagged texture that also alters the colour of the flower, making it more blue. But why do this? Speaking with Will Tingle, from Cambridge’s Sainsbury Laboratory, Edwige Moyroud…
Edwige - We were really surprised to find that all sorts of plants keep creating the striations. And what was interesting is that they're not perfect. So what I mean by that is they don't have exactly the same thickness. They have a bit of variation in how spread they are on the cell. And this is what we call disorder and different flowering plants had different amounts of disorder. But this disorder always creates the same color, always shifts the effect toward the blue UV end of the spectrum. And that was the first clue that this wasn't by chance because in theory you could create disorder that creates all sorts of different colors. So why is it that it always shifts toward the blue? And one thing we know about is that actually blue and UV are colours that pollinators can see really well. We can't see in the UV, but lots of insects can. So our idea was maybe this is a way plants create blue. And this was particularly interesting because it's quite difficult to make blue by other means. Using pigment to make blue is really tricky. People have been trying to create blue roses for a long time and it's never worked. It's never blue. It's like dark purple. And one idea we've got, it's also quite expensive and complicated to produce this pigment, whereas the cuticle is there no matter what. So creating the striation is quite simple and it's a nice way to appear blue when you shouldn't because you don't have the right pigment for it. So this was just an idea. And then we did all sorts of bee experiments to see if really bees can see it. And the long story short is, they can see it. And actually if you create this striation, if you create this blue effect, it makes the flowers stand out more. So instead of spending a lot of time looking for flowers, the bee can see them much more efficiently. So our idea is that by creating this kind of structural color, this allows flowers to really stand out from the crowd and it gives them an advantage.
Will - Was this striation the same in a plant that lived here as opposed to perhaps the same species of plant that lived in the tropics?
Edwige - We use a collection of the garden. So lots of these species are not native to the UK. Some of them are weeds and they spread everywhere. Some of them are much more local. So in theory, this kind of phenomenon can happen pretty much everywhere. What we realize is it's not so much a characteristic from where the plant lives, it's more a characteristic of the flower. So you can have flowers, complex shapes. Some are really close, some are open. What we realize is all the flowers on which we detected this, they're kind of simple shapes, a bit like a cup, meaning that they are directly exposed to light. Because if you develop striation inside the flower that's closed, it makes little sense. You can't interact with the light. So it's more characteristic that these flowers have. The other characteristic is many of them that don't remain open for very long, meaning that they have one shot at attracting pollinators. So maybe that's an extra selective pressure to be really shiny and really attractive.
Will - How does that play into our ability to conserve insects? Because a third of our food is created by pollinating. So hopefully that means that we could perhaps use this information to better conserve them.
Edwige - Yeah, absolutely. So in theory, one of the motivations we've got to understand how plants fabricate this structure is once you understand how they are made, it gives you you the ability to maybe engineer them, make them better, or transfer them to plants that cannot create this structure. So we haven't generated striation in plant that can't striaite yet and study the effect. But in theory it's something we could do. And more importantly, without even modifying the plant, this can give us some idea of, if you want to enhance pollination, what kind of species would be good to introduce to a new medium? What kind of species are likely to stand out. And species called iridescent species, the species that can do this trick of the light, might be a good way of making flour more salient.
Will - And how do you think this can help us conserve these plants?
Edwige - In terms of conservation, it's difficult because we are a long way from understanding how the pollinator interacts with the plant in its natural habitat. All the experiments we've done with pollinators are in control condition, which is really helpful for us because we can be sure that what we observe is really due to the specific traits. So presence of striation, ability to create a colour. What we need to do next is to go into the field and really observe what is happening. Especially we have some regions where we are very similar species, but some with striation, some without. And there is at least one case when the species without striation seems to be declining. So it's easy for us to say, huh, it's declining because it's losing the striation, but we don't really know. So that's one thing we need to understand better.