Naturalist Selections is an interview series produced by the American Society of Naturalists Graduate Council. We showcase graduate student and postdoc authored work in The American Naturalist, a premier peer-reviewed journal for ecology, evolution, and animal behavior research. Catch up on exciting new papers you may have missed from the journal, and meet some truly brilliant early career naturalists!

In this episode, Basabi Bagchi chats with us about new paper Bagchi et al. 2022: ‘Carcass Scavenging Relaxes Chemical-Driven Female Interference Competition in Flour Beetles.’ We talk about the difficult life of a female flour beetle: toxins, cannibalism, disease, the usual. Clearly, a bag of wheat is not the paradise you think it would be! But all is not lost – it turns out that a female beetle’s behavior can affect not only her own fitness, but also that of her group mates. You can read Basabi’s full paper here: https://www.journals.uchicago.edu/doi/10.1086/717250.

Hungry for more beetle talk? Email Basabi at basabi.bagchi_phd17@ashoka.edu.in!

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Credits

Featured Guest: Basabi Bagchi, Ashoka University, India

Host, Editor, Producer: Sarah McPeek, University of Virginia, US

Original Music: Daniel Nondorf, University of Virginia, US

Transcript:

You’re listening to Naturalist Selections, an interview series featuring graduate student and postdoc-authored work in The American Naturalist, produced by the American Society of Naturalists Graduate Council. Today we talk with graduate student first-author Basabi Bagchi about her new paper ‘Carcass Scavenging Relaxes Chemical-Driven Female Interference Competition in Flour Beetles.’ Basabi is a PhD candidate with Dr. Imroze Khan at Ashoka University in India. Basabi and her labmates study how behavior can mediate the negative consequences of crowded living conditions in the flour beetle Tribolium castaneum. When many female flour beetles share few mating and food resources, they produce toxic chemical secretions that reduce each other’s egg production. So what’s a female flour beetle to do? In a series of detailed experiments, Basabi and her lab mates investigate how females may overcome these negative effects. Interestingly, they find that females don’t move away from crowded areas. Instead, females can improve their fecundity by scavenging the carcasses of larvae for added nutrition. Females feeding on carcasses also produce fewer noxious chemicals than females who only eat wheat. Hence, an individual female’s behavior could help mitigate costs that affect her whole group. I spoke to Basabi to enrich my understanding of these fascinating behaviors.

Sarah

I’ve read so much about these flour beetles because they’re such a classic system to work with for all these kinds of behavioral questions. I’m really curious what your setup looks like and what you observe when you’re watching the beetles foraging and interacting with each other.

Basabi

Okay, so these are quite tiny to begin with. The thing with these beetles is they live where they eat, basically. So these are actually maintained in boxes or jars or whatever sort of setup that you want to have. It could be a box, it could be a jar and that is essentially filled with the wheat flour which they live on. So you have a bunch of beetles, you sort of give them just put them together in a boxand you let them lay eggs and once they lay the eggs you have this sort of a strainer sort of thing where you’ll to strain these beetles out. And this flour which passes through the sieve which has the eggs, this goes for incubation. Now the beetles that I work with are the populations that I work with. They have a 35 day discrete cycle and these are holometabolous which means that they have different life stages. So start with egg, then they have larvae per adult. So at the pupil stage we basically collect the beetles, we sex them and we store them in these plates which are 96 well plates. Now, 96 well plate is something which is very known to people who work with molecular biology but we use them to store beetles actually. And each well houses one pupa. Yeah. So we have a 96 well plate which has 96 pupa in it and then we give them this time to mature sexually for two weeks. And for us because we are working with carcasses, we had this period where we had to generate the carcass. So for them we use larger carcasses. So in between this maturing period we had to give another set of egg laying to generate our carcasses. And because the beetles were sexed previously we just had to sort of put them into different sex ratio treatments like male biased female bias that’s there in the paper. And we added the carcasses which were sacrificed on the day of the experiment primarily. But what I’d like to mention is because we had these sex ratio treatments, what was exciting or what we had to do before doing all of this is prepare the plates. So what we used was essentially 35 millimeter plates which is a small place and these were previously filled with flour. We had to Mark them even if you had the experiment today. So these sort of preparations needed to be done like three, four days before the experiment. Sure, because as the setups are really big so they take up almost the whole day. once you set the experiment it’s pretty fast. It’s about a ten day experiment and then you have most of your results by end of ten to 15 days.

Sarah

That’s pretty nice. So fast and very small. Weird question. Are you a baker at all?

Basabi

Yeah, I do like to bake.

Sarah

You do! I feel like the process of sifting the flour together, the beetles out is very much like what you do when you’re baking.

Basabi

Yeah, I didn’t fit that way. I mean it’s a good correlation actually. But Incidentally, I do like to bake. I love sweets, so I like making them too. Yeah, I mean I didn’t think of it that way actually. That’s a good point.

Sarah

I do want to ask you about the chemicals in the beetles. Is it quinones?

Basabi

Quinones.

Sarah

Quinones. Okay, I am saying that right. So these quinones that the beetles are releasing. The paper describes them as being from stink glands?

Basabi

Yes.

Sarah

Do they smell. Can you smell them?

Basabi

Yes, you do smell. Yes, they do smell. When you have a population, like I said, in a box, and that population is very crowded, the flour sort of turns a little pinkish, and you have a very pungent smell, which is there in the flour. And when you’re looking at them individually, when they first secrete these chemicals, they look yellow, and with time, they turn the flour pink, actually pinkish tinge to the flour. So the box also smells quite pungent. Interestingly, my advisor. So we have a prelude to this paper. So the previous AmNat paper where actually the work where they show that chemical interference is happening in these beetles? That’s how my advisor actually found out that quinones are playing a role, so he could smell that in the flour, and that’s how things escalated and that.

Sarah

Oh, wow. I love those stories where a whole research direction sparks from one weird observation.

Basabi

Yeah, exactly. Pretty much. The Scavenging work also is quite similar because who would think that eating a carcass would give them some sort of benefit? But that’s also, I was actually working with an undergraduate intern, and he was quite interested in looking at the effect of carcasses, not carcasses, essentially effect of cannibalism, primarily. And that’s how this work actually completely started.

Sarah

Mm hmm. Yeah. That was another question that I had is I think the experiments in this paper built on each other in a really beautiful way. But it kind of made me wonder if you had both of these alternative mechanisms for reducing competition in your head at the same time when you started this, or whether you tried one thing, found it totally didn’t work, and then went to the carcasses, or maybe you want to the dispersal second.

Basabi

A bit of both, actually. So we had this idea that these female bias beetles have reduced the fecundity or fitness in comparison to male bias beetles. And the first question that I asked what excited me as well as the other people in the paper as well is what could be possible ways to sort of get rid of such a decrease in fitness. Because how would this work in nature otherwise? And we sort of started on trying different ways that could relax its reduction. And obviously the first thing that would come to anybody’s mind is that they would run away from the site. And that’s what triggered the dispersal experiment. Essentially that would be the first thing to think that they would run away from a female-biased condition. And when we ran the experiment, we saw that that’s not what the case is. The female biased individuals or the females which are basically being guided or being regulated by the quinones, which are increasing the quinone levels are not really running away from the site. Instead the males are running away. And then we wanted to check for different increasing the resources. One would think that if it is a resource-based competition or since the females are reducing their fecundity and reducing the number of eggs they are producing, if you give them more food, if you’re getting more food, you produce more eggs. That’s what we thought. And that also didn’t really work out. And then finally it was just by chance or I don’t know, probably it was just by chance that we thought of another possibility is the carcasses. Because the thought simply comes from the fact that there’s a lot of literature on carcass feeding and cannibalism as well. To some extent that cannibalism does give individuals a fitness benefit or it acts as a source of protein. So that’s the direction that we wanted to go. And when we added these carcasses, we did see and that was really exciting. So when we first saw that when we added the carcasses and the fitness increased, that was like yes, maybe this is what is working. And that led to us doing more experiments. So it was very hypothesis driven, but it was also very exploratory study where one experiment actually led onto another. So when we did see that carcasses, see that this is happening, we just wanted to check if the quinoa levels are going down. If quinone levels are going down, then the question was if we change the kind of carcasses that we fed them. So we use different carcasses from different organisms, so we use Tenebrio molitor carcass and the consequence of carcasses as well. And also we used yeast, because, like I said, we were thinking, if proteins do play a role in elevating this reduced fitness, and both of them actually gave us similar results, that yeast, which is known to increase fecundity in many organisms, did increase the fecundity. Similarly, other types of carcasses also increase the fecundity. And that sort of told us that it’s not just one specific carcasses, instead it’s just protein source that they are gaining as a result of a dead carcass that is given to them to feeding to this. And ultimately, then we did try looking at it from different stink gland components, and we wanted to see that the stink gland components also reduce the fitness, and if it’s given in conjunction with the carcasses, that increases the fitness subsequently.

Sarah

Right. So if you give them the carcasses that can rescue the negative effects of the toxins.

Basabi

Exactly. And we give them the toxins and carcasses together. So what happens? Exactly? That’s what we thought. So technically, one experiment led to another and, I mean, it was really interesting to work on because technically we are depending on the results of one experiment leading to another experiment. So we sort of build up our hypothesis on the way. So it was quite an exciting journey.

Sarah

Yeah, it sounds like it. I was really curious about how feeding on the carcasses reduced the quinone production itself. And you mentioned in your paper that the quinones are produced often as a stress response, you think to crowded conditions. Which made me wonder whether there is some antagonistic component to the chemicals these females are producing or whether maybe it’s just a consequence of being in crowded conditions and the female’s behavior is really to reduce that competition, not to attack each other with chemicals.

Basabi

That is actually a very interesting question that you ask. There could be multiple components to this. But coming to the crowding aspect of it, you would think that if they are crowded, they’re not getting enough resource and that is leading to probably them having a less amount of fecundity. But what our experiments suggest as of now is that if you increase the resource content, by resource I mean the wheat source. If you increase the wheat, there’s not really any relaxation of this reduction in fitness. However, that relaxation happens as a result of nutrient quality or increase in nutrient source which is given to them in terms of carcasses. The other section would be you might expect that if females are in female biased condition, one female would possibly have higher fitness, the others are sort of paying the cost of one female having the higher fitness and others are secreting quinones, which is decreasing their fitness. But previous work also suggests that if you have a group size of the group size that we had four individuals: three females and one male, all three females should reduce fitness. Increasing the female fitness at the cost of other females possibly is not the case. However, it is quite an interesting way to think about what could trigger them to increase the quinone production in general, but essentially because it’s a stress response, I think any sort of stress would trigger the quinone production and probably female biased females, since they detect more females in the vicinity, they maybe capture them as a threat, or maybe detect them as a threat, which would maybe reduce the success of one particular female egg becoming an adult. And that probably triggers them to release more quinones, but definitely more work on this chemical aspect of it is needed to understand what actually triggers them in population level to increase the quinone production which has where they have to pay such a huge cost.

Sarah

Yeah, that’s really interesting. That makes me think about a lot of things. I guess I’m curious about in nature, if you know whether there are conditions where the beetles might not have access to scavenging carcasses, or whether you think carcasses are always available because individuals are always dying and others are always eating them.

Basabi

Okay, now again, you could think about it in multiple different ways. So the carcass that we are providing to them here are basically their offspring, not their offsprings per se, but offpring from the same group of individuals which are conspecific, which is technically cannibalism. Now in nature, if you assume a population, they will always be laying eggs and these eggs would always become larvae and then they would become pupa and ultimately adults. So if you have a bunch of adults laying egg, they would technically always have a source of carcasses. So it’s difficult to say that a source where they will not have any access to carcass because since these are cannibalistic in nature, they see it on their own  conspecifics, and that is sort of the source of carcass for them.

Sarah

Yeah. I was just thinking about whether in different populations there might be different strengths of selection on carcass scavenging behavior.

Basabi

Exactly. This actually makes me think that if there’s a population which has a lot of resource where the adults would and not a biased sex ratio bias condition there the scavenging behavior might not be as much as opposed to a population which has very little resource. So if you think about a population living in a huge sack of wheat, they would not want to feed on their own carcasses and all of them would probably hatch eggs and they would become adults. On the contrary, if you have almost an empty stack of wheat where there are like 5000 beetles living, they would probably kill each other and feed because they don’t have enough resources. That’s just an idea. That just possibly an idea.

Sarah

Yeah. I also think it’s really interesting because you might expect a lot of insect species will supplement their diet, females will supplement their diet with protein to increase their fecundity. But it’s still surprising to me that the beetles are not doing this in high resource conditions where they’re not having to share with a lot of other females. And it really does suggest that it is the chemical production that’s affecting their fecundity and not the lack of other nutrition, which is really odd.

Basabi

Yes, precisely. So, I mean, these chemicals actually are a trigger for a lot of things in general, but because it’s a stress response, possibly that also leads to them scavenging for more nutrients because they would probably because they are investing in sort of elevating the stress, they would not invest enough in egg production and that is sort of compensated by the carcasses. That’s what possibly could be a way of thinking about it.

Sarah

Interesting. I obviously have questions, but I’m sure you also have a lot of questions coming out of this work. So what is your next experiment that you would want to do based on this paper?

Basabi

There are multiple things that we would want to do. Uh, another aspect of the study which we have sort of discussed a little bit in the discussion as well, that we saw was if you alter the kind of carcasses that we are giving not in terms of the species of carcass but in terms of the quality of carcass, which means that if we have sort of an infected carcass given to them versus a good quality carcass now since they are feeding on these carcasses and if they are feeding on an infected carcass, that could be a source of disease spread and orally transmitted disease could go into the system and that could make them sick. So that is what fascinates me a lot. That how these sort of carcass feeding can lead to disease spread in the wild, can lead to change in the disease dynamics. And that’s what I would love to look at. So they might want to alter the carcass behavior. If you would like to think that there’s a two way thing to this, if you have a female biased beetle they have high quinone production, they would want more carcasses to deduce this. But if the carcasses of bad quality are infected, what would they do? Would they continue to increase their quinone production or would they want to avoid an infected carcass? We do have certain directions to this that indeed if you give them a choice between an infected and uninfected carcass, they do avoid an infected carcass, but what if they don’t have a choice? They just have infected carcass. Feeding on infected carcass does increase their fitness, but it’s not as much as uninfected carcass. And that opens up the completely new direction of infection avoidance behavior, essentially. And possibly another aspect of how disease can spread in a population through oral feeding or oral carcass feeding, essentially.

Sarah

Yeah. Oh, that’s so interesting. I guess it also really depends on the nature of the disease because as long as they get kids out of the process, selection says that’s fine. So there might not be selection against feeding on diseased carcasses if they’re still producing offspring.

Basabi

Exactly.

Sarah

But if there’s a dramatic reduction in the number of offspring they’re producing when they’re feeding on the carcasses. Then maybe that could lead to a change in behavior?

Basabi

also another thing I just have to ask. If the disease is transmitted from the mother to offspring, that would also have a selection against speeding on such cartels because they are laying on infected eggs and these offspring are not viable, then there would probably be a selection against feeding on infected carcasses.

Sarah

Yeah.

Sarah

Yeah. I mean, females beetles do tend to provision their eggs with a lot of their microbiota. So if some of that is disease, that’s a huge possibility that they’re passing that on.

Basabi

Exactly. And that probably could change their carcass feeding behavior as well.

Sarah

So do you think that that might be a case where dispersal would be a more adaptive strategy?

Basabi

Oh, well, yes, that’s something that we also wanted to look into. But there are so many things that could come out of this. Living with infection and how that can trigger dispersal is really interesting to look at.

Sarah

Yes. It seems like they really don’t like to move, though. So maybe they wouldn’t. I don’t know.

Basabi

Exactly. I mean, it also depends on the cost that we are paying. If the cost of living in the site is too high, possibly that might trigger the dispersal.

Sarah

Yeah. Man, being a beetle is hard.

Basabi

That’s true.

Sarah

You’ve got to eat, but you have to balance so many different consequences of that.

Basabi

I want to think that they just eat and lay eggs, but that’s just not it. There’s so many more things to it.

Sarah

A bag of flour is not the paradise that we thought it would be.

Basabi

Exactly. Yeah, definitely. So I really liked the fact that you liked our paper. So that felt really nice. So this is technically my first work. Thank you. So the other paper was published earlier, but this is actually the first work I started with working in the lab. That really feels nice when somebody says nice things about your paper.

Sarah

I mean, it’s the culmination of years of blood, sweat and tears and toil and passion.

Basabi

Yeah, and waiting also for the results, for writing the thing up, for the whole process. It’s a long process. Since we are quite a new lab, these were the first set of experiments that were being done in the lab, and we were all in the learning stage and we did really have a great time doing the experiment. That was a very interesting experience because we worked as a team. We were working together towards one goal. So that was a very nice experience. I really loved working on this paper. Probably I’ll remember this for the rest of my life.

Thank you so much, Basabi, for a very interesting discussion! Congratulations to all the co-authors, and special congratulations to Basabi for publishing the first paper from her PhD work. It’s brilliant. Thank you to Associate editor Matthew Schrader and the reviewers for their work on the paper. Thank you to Daniel Nondorf for composing our beautiful intro and outro music. And thank you for listening! If you’ve still got questions, and I’m sure you do, go read Basabi’s paper and then ask her for yourself! I’m grad council rep Sarah McPeek, here to keep the conversations going.