SOLS Podcasts

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Peggy Coulombe: Hi, this is Peggy Coulombe of the School of Life Sciences at Arizona State University, and welcome to Science Studio. With me is Juergen Gadau, assistant professor in the School of Life Sciences and a researcher in the Center for Social Dynamics and Complexity at ASU. Today he and I are going to talk about how genetic studies of some solitary insects can potentially reveal stepping-stones behind the evolution of species and sociology in insect society. Welcome, Juergen.

Juergen Gadau: Welcome.[laughter]Thank you for inviting me here.

Peggy: As I understand it, your favorite model organisms are hymenoptera, which are ants, bees, and wasps. Pliny the Elder, a Roman scholar who penned the book "The Natural History" way back in 77 AD shared this fascination, mainly for bees and hives. Why is it that social insects have captured so much interest for so long?

Juergen: I think because they are resembling a little bit us, or they were taken as models for what would be the ideal society. You have individuals, as in honeybees, which donate all their life and energy and resources to a bigger being--society. The other thing is that it was one of the first species which humans take in as agricultural species, so they had them around. Of course, people were interested in how it really functions, how it works.

Peggy: Did your interest in insects start early in your childhood, or was it something that you came to later?

Juergen: No, I didn't have a particular interest in insects when I was younger. I started out with watching birds and particularly was interested in plants. I never wanted to go into animals. Then later in university, I got interested in more theoretical issues like speciation and evolution.Insects have a great advantage over other systems. First of all, they have a short generation time. Since evolutionary changes accumulate over time you don't want to work on elephants, which live 30 or 40 years and you get one generation, or two if you're lucky, in your lifetime. On the other side, bacteria or microbiology wasn't that interesting because you couldn't see things. Insects were a compromise.I got drawn into insects more and more because they are really fascinating. That's the group that has the most species. If you look at their variety in forms, colors it's very fascinating. And also, all my plant professors were really boring.

Peggy: [laughs]

Juergen: The professors who truly attracted me most were working with insects.

Peggy: And you decided you wanted to be one of those interesting insect professors, as opposed to a boring plant professor.Tell me what distinguishes a social insect from a solitary one, besides numbers.

Juergen: You speak about social insects or a species becoming social when one of the individuals gives up part of its reproduction to help another individual to reproduce. That's what we call an evolutionary sense and altruistic behavior. Humans, usually, if you talk about altruism it's more broad-scale concepts--saying he's altruistic or she's altruistic.It helps a little bit if you can think about a family: the mother produces offspring and her daughters, instead of going off and producing their own offspring, help the mother to rear more offspring. That only makes sense if the chances of the daughters going out and getting their own families is very low. But if they stay they can get at least some of their genes (more sisters) to the next generations. In that sense whenever we have a situation where it doesn't pay off to go off on your own and produce offspring on your own then we will have a scenario where social behavior can evolve.

Peggy: Why are social insect colonies good experimental systems to study questions regarding the evolution of complex systems?

Juergen: The complex system simply defined would be a system where multiple points interact with each other. An insect colony is a prototype for that. You have small insect colonies who may have 10 or 20 individuals, larger you have millions of individuals, each interacting potentially with each member.Having these systems is simple enough so that you can do experiments. You can take colonies into the lab. Then you set up groups of 10, 20, 50, 150 and you can observe their behavior. You can write it down. The pattern we see is different in a group of 10 to a group of 1000. We see, for example, more division of labor. In a group of 10, everybody does basically everything. In a group of 1000 we have specialists for each particular task. That's why--you can bring them in the lab, you can observe them, it's easy to handle, and you can manipulate it, which you can't do as easily with other kinds of systems.

Peggy: Harvard University professor emeritus E. O. Wilson, the father of sociobiology and biodiversity, and a pioneer in the study of ant societies, started watching ants when he was a boy. His contributions and those of his colleagues like Bert Hoelldobler, who is here at ASU, have changed much of what is presently understood about insect societies. With so much focus for literally thousands of years, why do you think it's only been recently that gains have been made in understanding some of the mechanisms behind the evolution of social insect societies?

Juergen: I think previous generations knew a lot as well. We are only so successful because we stand on the shoulders of our previous generations. The advances we have made are mostly in the "proximate mechanisms"--that means "how do things function?--because we have over the last 30 years the revolution in molecular biology. Initially this was pretty much targeted to model organisms like Drosophila and the mouse. Now all these advances have been trickling down to other systems and it's now feasible to do a lot of things which where were unthinkable 10 years ago to do in honeybees or in ants.We have the complete genome sequence from the honeybee. That was something which when I started studying 20 years ago was unthinkable. They predicted that we'd have the human genome sequence in 2030, something like that. That certainly made a big, big difference in our contribution. Plus, I think that there were considerable [inaudible] associated with sociobiology in the 70s, focusing on research into the social behavior or the genetic basis of social behavior, and that also helped.

Peggy: My understanding was that the bee genome was only sequenced once in this past year, correct?

Juergen: The sequence has been published this year. The actual sequences go back about three years, but it takes a long time to basically compile everything. Just getting the DNA sequence does not tell you where the genes are. So that is a process which takes hundreds of researchers one to two years to complete.The actual genome sequence was done three years ago, but then the annotated - so where the genes are in the genome, what the functions of the different parts are, how the order is - that has been published just this year.

Peggy: While we commonly hear and talk about ant colonies and bee hives, and have for centuries, we hear less about species that live solitary lives, and almost nothing about wasps, for example, much less of specialists like parasitoid wasps or wasps that prey on arthropods of various types. What made you focus first on solitary wasps, and then in particular on the species Nasonia, which is a solitary parasitoid wasp?

Juergen: The first time I heard about Nasonia was when I was looking for a species I could compare a solitary hymenopterans -- or a species which belongs to bees, wasps and ants -- which I could compare to social ones. That was when I went as a postdoc to U.C. Davis and worked with Rob Page, who is now the director of the School of Life Sciences here.I was looking around because honey bees have an incredibly high recombination frequency, which was a trait which is very important and interesting for evolutionary geneticists. In order to understand whether it evolved in honey bees, or in ants, or bumblebees, or whether it was already present in the very primitive, solitary hymenoptera, I had to have a species which is solitary to look into that.People actually worked on Nasonia since the 1950s. I connected with Jack Werren from the University of Rochester who has worked on these species for quite a while. When I came in there, I produced the first genetic linkage map to answer the question, "Is the recombination frequency high or low?"It was low, so it was a specific adaptation of a social insect. In the meanwhile, I have done a lot of other studies which, more and more, say that this particular characteristic is a very specific adaptation of social insects. Bees show it, ants show it.

Peggy: The low recombination rate?

Juergen: No, the ants and bees have a high recombination rate.

Peggy: OK.

Juergen: The solitary ones have a low recombination rate which is very common. Drosophila, humans -- we all have a relatively low recombination rates. It's something about living in large societies which leads to the evolution of this higher recombination rate.We think it's connected with the increase in parasitic pathogen loads in those groups. If you have multiple organisms living together, it's a good target for parasites. We know that social insects have a higher load on the parasites and pathogens, so that may be an adaptation coming over there.

Peggy: Why did you choose a parasitoid wasp?

Juergen: I chose the parasitoid wasp, one of this was by accident - there was a lapsed species. The other thing was that parasitoids are especially important in ecology and also in agriculture, because they are one of the dominant factors which keep insect populations in an equilibrium.If you take away one of those parasitoids, they usually have an explosion in numbers of these particular insect species which usually have been targeted by these parasitoids. We see that often. If we import a particular species by accident or on purpose into a new habitat like from America to Australia or from South America to Europe, usually they lose their parasitoid. Then we get basically what we now call a pest species, which kind of gets in competition with humans for the use of wheat or corn or whatever.Parasitoids are used heavily by a control. For every insect, for every toad or snail, you usually have a parasitoid. In order to, instead of using chemicals, to combat pest species, you could also use bio control.Parasitoids usually lay one or multiple eggs on that particular insect, either inside the body cavity or on the outside, but the larvae hatch and eat the insect, so they basically lead to a decline in these pest populations.This group I'm working with is about 400 species that are currently used for bio control purposes. That's also where I use the egg because we're interested in how significantly supported to sequence a genome for the Nasonia. For the Nasonia, the genome has been sequenced right now. We are in this process to annotate the genome for Nasonia.

Peggy: How do you feel the study of Nasonia, a solitary insect, can contribute to the understanding about how social insect societies evolved?

Juergen: In order to understand what change - if you go from solitary to social life - you have to have the original status. If you only look at the social one, you see a specific state of a character, but you don't know whether this was already present in the original solitary ancestor, or whether it has evolved in concert with the evolution of the social behavior. It is a necessary step.You need to know what the ancestral status was, or what the original status was, to show what has evolved, what has changed. Some things may have not changed and just the use of it has changed, so that we now see no new genes but a different use of the genes.

Peggy: Do you think there is a, so-called, social gene?

Juergen: It depends on your definition of what is a social gene. There is, I think, not a new gene which occurs in a population as a mutation and it makes you social. However, there are some genes, or new alleles, coming into a species which may define them as social genes.One prerequisite, for example, is usually if you have individuals which are solitary they are mutually antagonistic, so they are aggressive. If they get too close together in a close space, they try to avoid each other at first. If avoidance doesn't help, they become aggressive and fight against each other. Very similar to us too, right?

Peggy: [laughs]

Juergen: If you put two students or professors too close together, eventually, they will fight.

Peggy: [laughs]

Juergen: So in order to overcome this kind of behavioral traits, you have to have the evolution of tolerance--tolerance of other individuals of the same species in a close space. And so, if you define sociality as tolerance of other organisms, there certainly is, not a chain, but a new kind of allele changing the behavior.So in that term, there may be social genes, but not in the other term, that you have, say, a mutation, and then an allele pops up, and all of a sudden, you're social. I think that's nonsense. But there are changes in how genes get used in social insects, compared to solitary ones, and we might call those social genes.

Peggy: I've read on your website that Nasonia is also a good model for understanding speciation; that is how separate species of organisms arise from a single common ancestor. How can something that typically takes such a very long time to accomplish be modeled in a lab with Nasonia?

Juergen: One of the big questions, and indeed, most of the time speciation takes hundreds, thousands of years, so it's a long process. But what we can do is we can look for traces of what's happened in the past, by comparing multiple species. So Nasonia actually has four species. And usually, a species is an entity which cannot mate with another species, right? That's what we call the biological species concept.In our case, we see there are good species. They are usually isolated. However, we bring them in the lab and we force them, so to say; they mate, and they produce hybrids. These hybrids are kind of moderately fit. If they reproduce, that's just the second generation, a lot of them die. Even a higher number of them are sterile, so we know there is already some kind of genetic factors which do not allow the hybridization.And so, when we talk about speciation, under this biological species concept, the mechanisms are the evolution of barriers against hybridization. And these could be what we technically call post-zygotic hybridization periods. So that means that offspring of two individuals from two different species, they may survive, barely, but they're not able to reproduce. Like a horse and a donkey. If you cross them, they produce a mule. The mule can survive, but it's not reproducing because it's sterile.So what we do, we produce these hybrids, and then we look for these genes producing or generating these incompatibilities, and so we can map, actually, the number of genes which cause this incompatibility, and along the phylogenetic tree--so their relationship over the history--we can see, "OK, the ancestor of this species had already this gene, and it's causing incompatibility with the other two." But between the other two younger species, we don't see these.So basically, that helps us identify the genes leading to these incompatibilities. And we also do that for behavioral assays. So the courtship behavior difference between those four species, and so we map those genes. And under the biological species concept, these would be considered speciation genes, because they prevent hybridization.And in that kind of case, we're looking at speciation within the lab. So we're not looking at, "OK, we'll breed them in the lab and then generate new species." No, that's taking a long time. So the youngest species pair here is thought to be about 250,000 years ago, when they had the last common ancestor--which is young, for a species.

Peggy: [laughs] I understand that you're part of a group, along with Baylor College of Medicine and the Human Genome Sequencing Center, and other researchers, who are interested in sequencing the genome of Nasonia. And so, tell me, what's the value in developing the first full genomic sequence for a parasitoid wasp?

Juergen: There are two arguments which we made. One argument is more like the basic, about getting these speciation genes. But I think the other, more maybe far-reaching argument is that parasitoids become really important for bio-control. I mean, if you can use a parasitoid instead of a chemical, it reduces the chemical load in our environment and improves our health.And so we don't know, for example, what host specificity in these parasitoids causes, so one of the big problems is to find the right parasitoid for the right pest species. If you understand these genetic bases to that, we may be better off choosing the right parasitoid to control the right pest species.And one of the big drawbacks, often, in these taking a parasitoid from one habitat in the new habitat, it could also target, not the pest species, but a closely related species. So it could kind of broaden its host range, and then potentially endanger the survival of other native species which we don't want to harm.Again, the Nasonia genome could inform us what the underlying genetics is and give us something in our hands to make it more predictable; another tool where we can say, "OK, the likelihood that this species changes its host and kind of targets native species, which is maybe endangered, is very low." So that would be another advantage of having the Nasonia genome in here.

Peggy: So tell me something about some of the other projects you might be looking at in your lab.

Juergen: I'm mostly working on the second project. It's on ants and ant colonies. And within ant colonies, all ants are really social. But you have further developments. You have ants which have a more, say, primitive lifestyle--not a strong division of labor--and you have ants which are highly complex systems with millions of workers.Usually, we think about that the original status in ant colonies is a single queen, and then, later in the development, in the evolution of ants, you get multiple queens. Same thing with single mating versus multiple mating. And so I'm very much interested in what changed during the course of the evolution, from, say, becoming primitively social, towards these really advanced societies which have different features towards the primitive ones.And so I'm looking at the evolution of mating frequencies, the evolution of queen numbers, in the ants. And ants are particularly good, better than honey bees, because we have about 10,000 described ant species. We have a huge of diversities in lifestyles, diversities in colony composition. Honeybees have only six species. Most of wasp species or bumblebees have much lower numbers. Bumblebees we have worldwide 5-600 species. In that sense if you want to look into the evolution of trades associated with the evolution that is in societies -- different trajectories, different life histories -- I think the ants are good.I picked two of them. We're now currently looking into, together with Gro Amdam and other researchers around here, how the change in the physiological status--not new social genes, but just change of the use of those genes--have lead to division of labor. That's another line of research I'm taking.

Peggy: What kinds of things would you like pursue in the future?

Juergen: I want to go on with the research in speciation, because now with having the Nasonia gives me exciting new opportunities to really get to the genes which are underlying these speciation events.This is a very unique situation. There's only within animals a second system where if you looked in that, even in drosophila, so this is a very promising line of research.The other one is using this model and going into biomedical research in terms of aging. So Nasonia, for example, they undergo a diet pause. That means that individuals can stay alive in a sleep-like status for half a year, up to two years.

Peggy: Is this between the larval stage and full adult stage?

Juergen: Yeah. Right. Whereas other individuals they go right through their developmental time: hatch, mate, lay eggs, and live like a month. These individuals can live like two years. This is quite a significant difference, and understanding what allows--what physiological changes, because they are generically completely identical--what physiological, behavioral differences allow an organism to extend its lifetime 20-fold. From a month or two months to two years. That's even more -- 40-fold.[laughter]The other interesting research which we currently follow: we have indication that a lot of those incompatibilities in the hybrids are due to malfunctioning of the mitochondria, the energy factories of our cells. These are very central players in our biology, in our survival. They are related to everything from aging, cancer to bad moods.[laughter]There's a system where we can move genes and mitochondria between species, allowing the setting of a new model for that.The other thing I want to pursue is working with colleagues from Argentina in South America, because the group of ants I'm working with here in Arizona has a sister group down in South America. The whole group is only occurring in the new world. We have about 50 species here in the deserts of the southwestern U.S. and Mexico. But we have nothing, and the related species are down in Argentina, Brazil, Chile.I had already a grad student from Argentina working with me. I'm in the process of getting a new grad student from Argentina. It's very fascinating to see that these have been separated for a couple of million years, these two groups, and see how similar environments lead to the same or different adaptations.

Peggy: You're originally from Germany. What do you think about Arizona, and what do you like best about being here?

Juergen: I like the open way people interact here at the university. It's more stiff in Germany. It's kind of a European prejudice, but it's to some degree true. Also, I like the heat. From my student time I worked in deserts, so I've experienced deserts enough--Africa, Australia, South America. I like this dry heat; it doesn't bother me at all. I'm more afraid of cold. It's a perfect place for me. Also I have to complain that this winter was really cold here in Arizona. [laughs] I was actually freezing. It's not supposed to be in the desert.

Peggy: What advantages were there here for you scientifically?

Juergen: Before I came here as a professor, I worked with colleagues here for five or six years--Jennifer Fewell, Jon Harrison, and Bob Johnson. It was some kind of a center for social insects, but mostly I came here because the ants I'm studying were here. When ASU started to hire like Rob Page and Bert Hoelldobler, all of a sudden we had a critical mass of people working on social insects. It became the center of the universe for any social insect researchers. That was very attractive to me.Plus I think ASU had a very nice offer for me to come here, so I applied for the job. The other thing is that my study organisms are very close by. That makes it really convenient. Otherwise I would fly over for a couple of months, stay down in the Chiricahua Mountains or around here with colleagues. It's different if you're around here for the whole year you can go out and you know what your ant's doing the whole year. You're not just getting snapshots of your organisms. There were a lot of advantages to coming here.

Peggy: [laughs] Well, Juergen, we're certainly glad that you came to ASU. Thank you for joining us today.

Juergen: Thank you for giving me the opportunity, and goodbye.[laughter]Or "tchuss" en Deutsch.

Peggy: We'll hope that some of Juergen's work turns into the discovery of a gene for tolerance in humans someday.[music]This is Peggy Coulombe, and you've been listening to a School of Life Sciences podcast, Science Studio. You may have noticed that we finally acquired theme music. Our music comes from the website Magnitude and was composed by Yongen from the collection "Moonrise."Just to remind you, the School of Life Sciences is in The College of Liberal Arts and Sciences on the Tempe campus of Arizona State University.

Social or Solitary: Is there a social gene?

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SOLS Podcasts 2007