The Hive Mind - How Ants Know Their Place
Chris - Now this week, we're looking at some of the creatures that live a colonial lifestyle and not just humans, but bees and ants. It's an incredibly complicated world inside an ant colony, with different types of ant doing lots of different jobs. In order to shed some light on what's going in there, researchers have found some interesting ways to follow individual ants around their colonies, and that includes gluing tiny radio tags onto each ant. Dr. Elva Robinson, from York University, is doing just that to find out how a colony comes to a decision, and she's with us today. Hello, Elva.
Elva - Hello, Chris.
Chris - Welcome to the Naked Scientists. Thank you very much for joining us. First of all, the question that must be going through everyone's mind - how on earth do you glue a radio tag to an ant?
Elva - Well, it's a very fiddly process and obviously, it has to be done under a microscope because the ants that I have been tagging are just 2 to 3 millimetres long, and the radio tags themselves are just half a millimetre across. Without a microscope, they just look like little bits of glitter.
Chris - And how do you stick them on?
Elva - Well I use just a very tiny, tiny amount of glue and put that onto the thorax of the ant and then placed the tag on top of that.
Chris - So Araldite or should I say Aral-mite perhaps?
Elva - (Laughs) It is Araldite that we use actually, yes.
Chris - And what did this show? What were the questions you were trying to answer by tagging these ants?
Elva - I'm very interested in how colonies organise themselves and how the individual ants contribute to the overall collective processes in the colony. The great thing about the RFID system is that it's possible to uniquely tag every ant in the colony so that each tag has got its own unique ID. So when an ant passes the RFID reader, I know which ant it is and where it is and what time it's been there.
Chris - Talk us through the experiment. So this is in a laboratory colony of ants, presumably, because it will be almost impossible to try and do this out in someone's garden...
Elva - Yes. With these tags, because they're so very small, they don't have a very long read range. So at the moment, it's only appropriate for laboratory use. We have several colonies in the lab. What I was interested in with this particular experiment is how the ants decide which job to do in the colony. You've got some ants which are looking after the broods and some which are caring for the queen, and others which might be patrolling the nest, constructing the cavity or going out and searching for food. I'm interested in how the ants decide which job to do and in this experiment, I changed the demand for particular jobs - for foraging and also for brood care - and looked at which ants switch to take on that extra job.
Chris - How do the ants know that x number of ants have gone out of the colony or that there's a certain amount of food out there they have to bring in? How is that message relayed around the colony?
Elva - That's the very interesting thing because the individual ants don't have any overall idea of those kind of things - of how much food is available or how much food is required. So, one of the things we're interested in is how does an ant know that it should go out and forage? And the RFID system meant I was able to look at a whole lot of different factors affecting the ants because I knew for each ant, where it had been before in the nest, and what jobs it had been doing previously. Also, I knew how old it was - the ant, and I knew how much fat it had got stored. I was then able to look and see which ants went outside and foraged when I increased the demand for foragers, and how that was predicted by all those different factors.
Chris - So is it a bit like humans, where we give the menial jobs to people who are pretty junior and we give the important jobs to the senior ones? Is there a pecking order in the ants or does it work out some other way?
Elva - Well yes, it's not quite like that. There are age differences in what jobs the ants do, so it does tend to be the older ants that go outside and forage. But what our study showed was that there's also big differences in how much fat is stored in the individual ants, and the fat stores are very valuable to the colony. So we found that although on average, the younger ants had more fat than the older ants, there was a lot of overlap in the distribution. And we found that it was the amount of fat that an ant had stored that was much more important than any of the other factors in determining whether an ant went outside.
Chris - So how do ants size each other up then? Do they have some kind of pheromone that's responsive to how much fat they've got on board and the fatter they are basically, the lazier they are because they get to stay indoors?
Elva - We don't really know what the mechanism of this is yet, but it's quite possible that the ant is able to perceive its own fat level through some kind of internal physiological hormonal process or even through its physical weight as it moves around. An ant only needs to be able to perceive its own weight, not that of the other ants in the colony. We suggest that as an ant gets leaner, it becomes more likely to go outside and forage. But this isn't just because it's getting more hungry because what the ants tend to do is go outside and forage, collect food, and then bring it back and pass it on to the other ants in the colony which were already quite fat, and those ants will then convert the new food to fat and store it. The other ants will remain lean and carry on foraging.
Chris - Is that because foraging is risky and when you go outside, there's a reasonably high chance that you're not going to come home?
Elva - That's a possible ultimate evolutionary explanation for what we're seeing. That the fat ants are very valuable to the colony and the lean ants are less valuable, and also, if they're older, they're less valuable. They might get lost through predation or they might just get blown away when they're outside foraging. But interestingly, what we found is that for the same level of fat, it didn't actually matter whether the ant was an older ant or a younger ant. So the age per se didn't really matter. It was the amount of fat stores. But on average, the older ants are leaner, so it is older ants which were going out, but it's not because of their age. It's because of their fat stores.
Chris - Apart from obviously being extremely academically interesting to understand how these complex colonies work - because there are thousands of individuals in the colony, aren't there? Are there any ways in which this can inform the big picture? Can we make human systems, computers and so on work better because of understanding how these organisms organise themselves?
Elva - These ants are great examples of self-organisation because each ant is making a decision based only on the information that it has about itself. It doesn't have to know the overall system of the colony and that's quite an important lesson for lots of human systems where we tend to focus a lot on centralised control where you have one control centre collecting all the information and deciding what to do. But obviously, if there's a problem with that control centre then your whole system will break down. For ants, decisions are processed in a very distributed way, so all the individuals contribute. And if any one individual is taken out of the system, it will still work. So in the case of our experiment, if some ants were removed as we did in our experiment, then the next leanest ants will go out. And if you keep on removing ants then more and more corpulent ants - more fat ants - will start to go outside. So it's all very self regulating.