The Genetics Of Becoming An Ant Queen

JOHN DANKOSKY: This is Science Friday. I’m John Dankosky. Ira Flatow is away. Living in a social group is complicated. You have to consider others, not just what you want and your own needs. Everyone needs to cooperate to organize all that needs to get done. And there are certain roles that need to be divided up to make the structure run. There are workers in the higher ups, this might sound like your office, but this also happens in the animal kingdom too. A group of researchers looked at how this occurs in ants, especially the division of roles in the colony. They wanted to know how does an ant become a queen or a worker?

They found out that it’s based on genetics, but not the way you might think, not in terms of who is related to whom. But they were able to pinpoint a certain gene that played a role in determining which ant becomes the queen. These results were published this week in the journal Science. My next guest is one of the authors and she’s here to tell us what this means about the evolution of social organization in the natural world. Ingrid Fetter-Pruneda is a post-doc research associate at Rockefeller University here in New York and she joins me in our CUNY studios in midtown Manhattan. Welcome to Science Friday, thanks for being here.

INGRID FETTER-PRUNEDA: Thank you so much.

JOHN DANKOSKY: Our number is 844-724-8255, that’s 844-SIDETALK if you have questions about ant behavior. So before we go directly to your study, I’m wondering if you could just take us inside the typical ant colony. There’s a queen and what other kinds of ants?

INGRID FETTER-PRUNEDA: Well you have a queen and the workers. And the workers normally do the foraging task and the nursing task. And then depending on the ant species, you can also have other types of workers, like the soldiers and these typically have huge mandibles. I don’t know if you have seen them.

JOHN DANKOSKY: Oh the huge mandibles, they’re just the pincers on the front.

INGRID FETTER-PRUNEDA: Yeah and that’s another kind of ant colonies.

JOHN DANKOSKY: And there’s thousands of types of ants right? And they all behave slightly differently or they all more or less organized the same?

INGRID FETTER-PRUNEDA: They is a lot of diversity but they are more or less organized the same. They all have– well most of them have queens that are the ones that reproduce and make eggs and then the worker class.

JOHN DANKOSKY: So ants weren’t always as social as they are now. They evolved from an ancestor that was a bit more solitary. What can you tell us about that?

INGRID FETTER-PRUNEDA: Well, first you have to imagine that you would lay an egg like the ancestor would lay an egg and then the egg would hatch into a larva and would have to feed and develop right. So what first happened was that something similar to well probably a wasp would parasitize something and lay an egg there and then this larva would hatch there and eat and then develop. But then the actual ancestor to ants started providing food to these larva and that’s like the main issue responding to the larval cues to the need of food.

JOHN DANKOSKY: Why exactly is it advantageous for insect to become social. I mean what’s the evolutionary advantage to developing the social behaviors?

INGRID FETTER-PRUNEDA: That’s a very difficult question and I don’t know the exact answer but what happened was that it made them more successful and you can have, for instance, a colony with just one queen laying all the eggs and due to this reproductive division of labor, and 10 millions of workers helping raise the young of the queen. So it made them extremely successful due to the fact that there was brood care and generations overlapping generations.

JOHN DANKOSKY: You say brood care, so this is the lots of workers taking care of the young essentially. That’s their job.

INGRID FETTER-PRUNEDA: Yes, exactly.

JOHN DANKOSKY: So in your study, you were interested in figuring out if there was a difference between the genes expressed in queens versus workers. You found that there’s one gene that was common in the brain of a bunch of ants. First of all, tell us how you pinpointed this one gene.

INGRID FETTER-PRUNEDA: Yeah so what we did is we compared across seven ant species the genes that were being expressed in brains of queens and brains of workers. And we found that there was these gene which happens to be an ant insulin who was always highly expressed in queens and low in workers. But it was by comparing these seven distantly related ant species that we were able to find this one gene.

JOHN DANKOSKY: So you’re saying this is a type of ant insulin. How are the insulin levels and reproduction related?

INGRID FETTER-PRUNEDA: So it’s related to metabolism and also in insects it known that it regulates how many eggs you can produce. With higher levels of insulin you can produce more eggs and you also increase like the nutritional stores and or due increase in nutritional stores you can increase the amount of eggs you produce, and that’s all regulated by insulin.

JOHN DANKOSKY: So at the top we were talking about this difference between the worker and the queen. And having read through your study and having tried to decipher this, I’m still unclear. I want to understand how does it determine which ant becomes the queen and which ant just goes around being the worker? Is it is it predetermined in some way genetically or is there something specifically that happens to one ant over another?

INGRID FETTER-PRUNEDA: So there are in many ants, in most ant species they’re all genetically identical and what happens is that due to differences in development and the amount of nutrition that they get, there’s like a variability in the size. And some will therefore have more insulin and that’s what we found. And they would also have more ovaries. But we tested all these in the ant species that we study in the lab so we were able to test our hypothesis in the specific ant species that we have now. But it’s related to amount of nutrition and development. Yeah, but genetically they are all identical.

JOHN DANKOSKY: So in your study, you are actually giving some of these worker ants these ants that weren’t reproducing a shot of insulin.

INGRID FETTER-PRUNEDA: Yes.

JOHN DANKOSKY: Right so explain exactly what you did and what you found.

INGRID FETTER-PRUNEDA: So we study very interesting and special ant in the lab, it’s the clonal raider ant.

JOHN DANKOSKY: The clonal raider ant.

INGRID FETTER-PRUNEDA: Exactly so and what’s interesting about this, and I’ll tell you briefly about this ant then how we injected them and tested the function of this insulin like peptides. So the clonal raider ant, all the ants in this colony look the same. You don’t have a real queen. However, they behave like queens for two weeks and then they behave like workers for two weeks. So it’s a different kind of ant species to the ones we were talking at the beginning. And so what we did in these ant species also, when they behave like queens, they have higher levels of insulin, and when they behave like workers they have lower levels of insulin. And so what we did is we got the ant insulin and we developed the particle to inject them.

And we injected and elevated the levels of insulin in ants and in ants that were behaving like workers. And we were able to activate their ovaries and therefore they were starting to produce eggs. And what is interesting is that what we discovered is that again the larvae, the young in the are repressing the ovaries that the sites of egg production in these ants. And once you remove the young, the levels of insulin the ant go up and then they activate ovaries and behave like queens.

JOHN DANKOSKY: OK so if there’s larva around, the ants are essentially being told to not reproduce and to take care of the larva. That’s their job now.

INGRID FETTER-PRUNEDA: Exactly.

JOHN DANKOSKY: And as soon as the larva go away, the ants essentially something kicks in and says, OK no more larva. We’ve got to make new ants.

INGRID FETTER-PRUNEDA: Exactly.

JOHN DANKOSKY: And that’s how it works.

INGRID FETTER-PRUNEDA: Yeah so yeah and that’s fascinating. How these genes became regulated– or not the gene, but the signaling, insulin signaling in general became regulated by the presence of the larva or the young, you know, the social context. That’s what is fascinating.

JOHN DANKOSKY: Now when you say social context in this context what exactly do you mean? Because I mean for us humans, when we think of socialization there’s an awful lot of things that go into that how we behave socially. When you’re talking about social behavior in ants, what exactly are you talking about?

INGRID FETTER-PRUNEDA: Well I’m talking about there are many things that they do that are amazing. But in this specific case I’m talking about the fact that they take care of the brood of their young you know. So the social context means that there are larvae present in the colony. And in this ant that I’m telling you that we study in the lab, in [? O’Connor’s ?] lab, the larvae always are present in during this cycle so they are all the same age. And then at some point they pupate and then you don’t have young anymore that are hungry and that need to be fed. And once they pupate then the adults can again lay eggs and produce a new cohort. So that’s super interesting.

JOHN DANKOSKY: You said that there are many amazing things that these ants do and you kind of get a smile on your face. You really I mean you find these ants fascinating in all sorts of ways beyond just this study.

INGRID FETTER-PRUNEDA: Yeah, definitely

JOHN DANKOSKY: Give me something else, what’s something else fascinating that they do in a social setting?

INGRID FETTER-PRUNEDA: Yeah well they help each other. They cooperate not just to rear the brood but, for instance, they build their nests together in other ant species and they do that by holding their legs together for instance, or they make bridges. There are many examples are they yeah– but this study in specific really gave us a lot of information of how the social environment which I mean by the presence of larva was regulating the behavior of the ants, the reproductive behavior of the ants.

JOHN DANKOSKY: Is there anything that we can learn from these ants that you’re studying about species outside of ants, about other organisms? Is it teaching us something about socialization?

INGRID FETTER-PRUNEDA: I would definitely say yes. We have learned I mean a lot about studying model organisms like yeast and flies, about how genes work, or what the function of genes are. We have learned a lot about studying sea slugs, you know and how– and not just sea slugs but giant squids. And now we have the opportunity to study something really complex, that is social behavior in a simple organism that is an ant. So I think we will learn about even human social behavior eventually by learning the basics of how such a complex system can work.

JOHN DANKOSKY: And that’s what you mean by a model organism, an organism that is able to teach us about others.

INGRID FETTER-PRUNEDA: Yeah, that is able to teach us about others and that we can do very controlled experiments in a laboratory setting.

JOHN DANKOSKY: So what’s the next thing that you’re studying? what are you working on now?

INGRID FETTER-PRUNEDA: Well we are studying also work or division of labor. So this was a reproductive division of labor. What makes them, queens and workers and how this could have evolved, which is a fascinating question. And so the next thing would be what makes them to behave like nurses or like foragers for instance that be another thing.

JOHN DANKOSKY: So it’s the real division of labor in terms of who’s going to do what to make sure that the colony works beyond just reproduction?

INGRID FETTER-PRUNEDA: Yes exactly.

JOHN DANKOSKY: It’s fascinating stuff. Thank you so much for bringing us these ant stories in your study. I really appreciate it.

INGRID FETTER-PRUNEDA: Thank you so much.

JOHN DANKOSKY: Ingrid Fetter-Pruneda is a post-doc research associate at Rockefeller University here in New York and she joined us in our CUNY studios.

Copyright © 2018 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/