Ant social stomachs

How many stomachs do ants have? Anatomically, the answer's one. But the real answer is - for some species at least - two, because, by passing stomach contents among themselves, the colony has a shared "stomach" that enables them to distribute resources among all the members. But it's even cleverer than that, because alongside the calories that go into that community larder are a whole host of signals that can help to control how ant society operates, as Adria Le Boeuf explains to Chris Smith...

Adria - All insects, including all ants, have three sections of their stomach. The first section, in some ants, has been commandeered into a social stomach. So it's basically this special sack that they use to hold food that they can then share with their nest mates, something that they can use to hold the nice things that they find outside foraging that they can then regurgitate and share. So we're talking about vomit here.

Chris - Nice. So is, the aim that they'll hang onto this and decide what carries on down the digestive tract and what gets shared. Can they actually exert control over what's in that first stomach?

Adria - We think so, they also add a lot of interesting things that they make themselves into this fluid. So it's not just food that they're sharing around. They're adding a whole bunch of other things in there, either products of their own metabolism or potentially manipulative things, helpful things. This is really exciting because it kind of allows a globalised metabolism over the scale of the colony. Well, this was the idea and that's what we wanted to test.

Chris - How?

Adria - One very convenient thing is that we can, you know, gently squeeze the ants in just the right way, and we can get them to regurgitate and share the contents of this social stomach. So we set about taking different ants within the colony, which we know how different roles: ants that care for the young, and ants that go out to forage. We thought we might see differences between colonies that have kind of different priorities. A young colony is just starting out and they need to rapidly grow. And a mature colony, they need to disperse: new queens, new males to start new colonies. And we thought maybe they would also be sending around different molecules over this social circulatory system.

Chris - And is that what happened?

Adria - What we found we are looking mostly at proteins is that yes, indeed. There are differences between different individuals, the nurses and foragers, and we saw differences, big differences between the young colonies and the mature colonies. The mature colonies seem to be passing around consolidated resources, big storage proteins. So it's as if they are very wealthy and they can consolidate their and process their resources and pass them around over the social circulatory system. While the young colonies, they were sharing simple processing of sugars and in the nurses and foragers these different ants within a colony, we saw that nurses tended to have some sort of anti-aging proteins in their, socially exchanged fluid. And that was cool because it presented two possibilities for why that might be. So nurses tend to be the younger ones, and they're also closer to the queen. And so it is possible that either they make more of these anti-aging proteins themselves, or maybe they're feeding them to the queen, or maybe other individuals in the colony produce them and give them to the nurses or give them to the queen. So, there's a lot more work left to be done.

Chris - Do these stomachs lie downstream in terms of signaling of somewhere else in the ant, or is the stomach the origin of, the signal? So, in other words, if the ant, does the ant get a pheromone, that then changes its behavior in a range of ways. And that impacts also what it does to the stomach contents, or is actually the stomach reacting to what's going into it and, doing something to it.

Adria - We have indications from work that we haven't yet published that other aspects of the, ants physiology control, what they put into the social stomach. We're also doing some work to see if they can perceive what they have there. Is there a message that comes in through the social stomach that they can then perceive? And we don't know. I mean, thinking a little bit about democracy and when is it worthwhile to be able to sort of have polls? It might not be worthwhile to be able to read the ballots that you're receiving.

Chris - The thing that's niggling me, that's, when you used the "V" word earlier, and said " vomit", it's something that we are programmed from an early age to be repelled by because of infection control implications. Is this used slash abused in the way in which infections are controlled or spread, or, other threats are detected and responded to in colonies?

Adria - That's a fantastic question. Yes. Ants are very susceptible to epidemics or illnesses because they live in close quarters like humans and things can spread like wildfire. There have been different results seen in different species about whether ants do more of this fluid exchange when they're sick, or less, there are some species that definitely do more of it. And when we look at the proteins in the social fluid, we do see a number of things that are related to immunity. So I think it's quite likely that at least in the species we're working with is that when they're sick, they produce more of certain things that they can then pass to their nest mates that can protect their nest mates from illness.

Chris - And have you tried manipulating it as in it's one thing, obviously, to do an observational study where you pick up an ant, you establish where it's pecking order is in the queue and, then see what's in its stomach. But if you add something to the stomach, can you change either the behaviour of that or the recipients?

Adria - Yeah. So one of the cool things that we've seen, this social stomach contains all sorts of things, more than proteins. There's small RNAs, there's hormones, there's lots of cool stuff, and we've done some work on the major hormones that we find there; they seem to be targeting the larvae. So when an ant colony is passing around a lot of this hormone called juvenile hormone, it makes the larvae develop into bigger adults and helps them develop faster. And more of them get reared to adulthood. It's kind of like a parallel to breast milk or seminal fluid, where there are all these different kinds of messages that end up in here along with the important cargo. And we've seen from studies in humans and model organisms that there are many things that can shift these kinds of, socially exchanged materials. What we're seeing in the ants is your social role, your behavioural role within the colony. Also the age of the whole colony you're with inside and all these things can impact what is being shared, which is very exciting because it means there's so much to discover in how these different components are manipulating receivers, are communicating important information, and understanding how groups really work together collectively.