How Flowers Are Turning Up The Heat

Chris - Here's Beverley Glover from Cambridge University who works on plants and has also found out how they're using jiggery pokery to attract pollinating insects. What's your work about and how is this all achieved?

Beverley - What we're interested in are the adaptations flowers have that make them particularly attractive to pollinators. If you think about a flower, the petals - the bright shiny bit that you like to look at - is really there for only one reason: to attract animals. Different plants have come up with different ways of making those attractive to animals. The one we've been working on most recently is miniature lenses on the petal cells that warm it up a few degrees. We've been doing some work with bumble bees in labs and in flight arenas to test whether they prefer warmer flowers and whether that would be an advantage if the flower could attract more pollinators in the wild.

Chris - And does it work?

Beverley - It seems to work. Having those lens-shaped cells makes the flower warmer and the effect is strongest at dawn and at dusk and we know that bumble bees need extra help at dawn and dusk when it's hard for them to get that big fat body off the ground to fly. So what we've been doing is giving them artificial flowers of different temperatures and seeing whether they prefer the warmer ones and whether they can learn which colours of flowers might be warmer than other colours. It seems as though they can. They can work out that some colours are warmer than others.

Chris - Because the dark colours absorb more energy?

Beverley - Well that would be one way of doing it and it certainly seems that in the wild, from our very early preliminary work, dark coloured flowers are generally warmer than light coloured flowers.

Chris - So why are they all dark then?

Beverley - Because there are all sorts of other ways of doing it and it's not just about warmth. A pollinating animal is interested in being able to spot the flower easily from a distance so it needs visual contrast to the green of the leaves. It also needs to be able to work out where to get into the flower at a short distance, and so there are short distance visual effects. And there's beginning to be some data from work of ours as well about them liking the feel of different flowers, so tactile effects might have a role too. So temperature is just one part of the bag of tricks if you like.

Chris - But why do they like it when it's warmer? Why should that be more attractive?

Beverley - For a bumblebee we think it's about metabolic reward. They need the sugar from the flower to make energy to fly but they, like you on a cold day, might get more energy more quickly from a warm drink than a cold drink. It saves them from using their own energy to warm that nectar up if the flower's already providing it at a warmer temperature.

Helen - And with the bumblebees it's all about being cold blooded. They're not like us mammals; they rely much more on their surroundings to get themselves warm and active for the day's activity.

Beverley - Yes that's right. There's a lot of evidence out there that many insects will back in warm flowers just to get the heat. What we've done that's different is just to show that just warming the flower up by a couple of degrees, just warming the nectar up to give a warmer drink, makes the difference as well. It's not just about sun bathing; it's about getting a warm drink as well.

Chris - How far back in evolutionary terms do you think this goes or is that a very difficult question to answer because there's not a fossil record for plants quite as well as there is for other things?

Beverley - You'd be surprised how good the fossil record for flowers actually is. But it's a difficult question to answer because there's probably a whole range of different ways of warming a flower up and some of them won't fossilise, so for instance tracking the sun. This is not something you'd pick up from a fossil and there are certain plants that do that. The cells we've been looking at, the little lens-shaped ones that warm the flower up, we know that around 80% of flowering plants have those including if not the oldest flowering plant family that's still alive today. Probably the second or third oldest groups have those cells, which suggests that it could have evolved quite early.

Chris - Because insects have been around for quite a few million years. So does that mean that plants have been up to this trick ever since then?

Beverley - It's an interesting question. There's a lot of debate out there as to whether the flowering plants, which are very very rich in species number compared to non-flowering plants, actually underwent that radiation into so many species because the insects were also radiating into so many species at the same time. In the fossil record there are a lot of flowering plants appearing as some of the insect groups expand, so it's possible that that link has been there for quite a long time but it's difficult to prove.