Bees prefer warmer flowers
Pollinators may be seeking more than just food as a reward when they choose one flower over another. Researchers at Cambridge University have found that bees bask in warmer flowers. They get a metabolic reward which helps in flight. Flowers it seems are cleverer than previously thought.
Robyn Williams: Did you hear Chris Smith on ABC Radio National Breakfast a few days ago talking about the way bees have been found to prefer warm flowers, seek them out in fact? The work was published in the journal Nature by Beverley Glover and Heather Whitney, and here they are with Chris.
Heather Whitney: We were actually starting out looking at conical cells which are raised on the petals of flowers, and this had been found to warm up petals. It had been observed before that insects appeared to bask in the warmer flowers. It hadn't been shown that bees had a definite preference for warmer flowers.
Chris Smith: I suppose it's obvious that they would like warmer flowers because they would get some energy for nothing.
Heather Whitney: Exactly. It is a metabolic reward, but instead of in terms of nutrition, it's warming themselves up, so helping with flight energetics.
Chris Smith: So how did you actually go and test this theory? What did you do?
Heather Whitney: We first of all tested to see if bees liked warmer nectar. This is basically where we just had two feeders, one which was at a cool temperature and one at a warm temperature, and then we just noted to see which of the feeders the bees then had a preference for, and consistently it was the warmer feeder. So we knew then that they definitely liked warmer nectar. We were then interested to see if the bees could use another cue to actually sort of seek out warmer flowers, so for that we used different coloured flowers, one of which was at a warmer temperature. The two flowers were fairly similar colours, there wouldn't be a colour preference because bees can show a colour preference, so one was pink and one was purple. And then we did the alternate experiment as well to show that it wasn't a preference for purple over pink.
Chris Smith: So the bees weren't particularly colour selective? They didn't mind the colour, it was definitely the temperature?
Heather Whitney: Yes, whether you did the pink as warmer or the purple as warmer, they consistently chose the colour that was the warmer temperature.
Chris Smith: Let's just turn to Beverley Glover who is one of the co-authors. Beverley, what are the implications of finding this?
Beverley Glover: Well, the implication that we're really most excited about is that flowers are cleverer than we thought they were. They can use tricks to persuade pollinators to visit them without actually expending any energy or much anergy, providing a greater reward. So this is a very simple trick; light is trapped into the flower and heat with it using a lens-shaped cell, and that costs the flower very little to produce and yet in exchange it gets the benefit of extra pollinator attention.
Chris Smith: Do pretty much all flowers show this?
Beverley Glover: There's quite a lot of variability in different systems for warming the flower. The lens-shaped cells or the conical cells that we're interested in are shown by around 80% of flowering plants, but they vary in how conical they are and how big they are, and that's one of the things that we're hoping to work on in the future is to try and actually get into more detail of different specifics of lens-shaped cells and see how they work.
Chris Smith: What about other insects?
Beverley Glover: You would expect that other animals would as well but you have to look at the physiology of other animals. For a bumblebee, flight is quite an expensive business and they do need, particularly in the mornings, to warm up quite a lot before they can fly. So it may be more significant for them than for some other animals, but then a humming bird also suffers the same constraint so it may also prefer warmer flowers, something we'd like to be able to test.
Chris Smith: Heather, in your experiment you looked just at artificial flowers that you'd created. Are you now going to go and say let's go and see if this is for real, can we do this with real flowers, and see if the same thing occurs?
Heather Whitney: We are measuring both Antirrhinum snapdragon flowers that have conical cells, and a mutant version that has flat cells. We're hoping to track how the temperature of these two different flower types which are identical in every other way, how their temperature changes through the day, and then we're also going to map onto that how the pollinator behaviour changes both between the two flower types and during the day to see if we can find a correlation between flower temperature and pollinator behaviour.
Robyn Williams: Heather Whitney and Beverley Glover in Cambridge with Chris Smith of Nature Podcasting. Nice to think of those little bees getting a warm cuddle among the snapdragons.
- Beverley Glover
- Department of Plant Science
- Heather Whitney
- Department of Plant Science
- Chris Smith
- Nature Podcasting
- Robyn Williams
- David Fisher