First up this week, Online News Editor David Grimm joins host Sarah Crespi to talk about how cats think about their own bodies . Do cats think of
themselves as a liquid, as much the internet appears to believe? New experiments suggest they may—but only in one dimension.
Next, freelance producer Ariana Remmel is joined by Ted Schultz, a research entomologist at the Smithsonian Institution, to discuss the evolution of ant-fungus farming . It turns out, ants and fungus got together when Earth was going through some really tough times about 66 million years ago.
This week's episode was produced with help from Podigy
Transcript
Sarah Crespi: This is the Science Podcast for October 4th, 2024. I'm Sarah Crespi. First up this week, online news editor David Grimm is here to talk about how cats think about their own bodies. Do they think of themselves as liquid, like so much of the internet thinks of them as liquid? A new experiment suggests that cats may, but only in one dimension. Next, producer Ariana Remmel is joined by researcher Ted Schultz to discuss the evolution of ant fungus farming. It turns out ants and fungi got together when the earth was going through some really tough times around 66 million years ago. Time for some cat myth-busting. Dave Grimm is here. He's our online news editor for science. And, you know, we talk about cats basically even if not for the podcast, if we see each other, we're gonna talk about cats. Hi, Dave. Welcome back to the show.
David Grimm: Hey, Sarah.
SC: So I've always heard that cats use their whiskers as a guide for tight spaces. You know, if the whiskers fit, so does the cat. You've heard that before?
DG: I've always heard that as well.
SC: We're gonna bust that myth today, I think.
DG: Well, I think we're gonna say that cats may be using more than just their whiskers to sort of figure out whether they can fit through something.
SC: They have more than just a measuring stick on their face to understand their bodies.
DG: Exactly.
SC: And, you know, their agility, their ability to balance and jump up to these like really high heights, you think, oh, they must have really good self-awareness of their capabilities. But then on the other side, there's these internet videos that show them failing over and over again to try to get on the top of the couch or on the top of the fridge.
DG: One of my favorites is a video of a cat trying to jump on the roof of a barn or something that shows all of these theoretical mathematical equations going on within a cat's head. And then, you know, after about 20 seconds of that, the cat jumps and completely misses the roof. So, yes.
SC: So, okay. Our cat love has come out full force.
DG: As always.
SC: Let's talk about the actual research here. What we're talking about is this, I guess it's cognition, right? In cats, like how much do they know about their bodies? How much do they have to think about it or can they think about it?
DG: It's something called body size awareness. It's this idea that it seems very obvious to us as humans. We know how big we are. We know how tall we are. We know how wide we are. Not because we think about our bodies all the time, but because we see ourselves. And when we see ourselves, we know that we see ourselves in the mirror that we're actually looking at ourselves. So it seems simple, but it's actually unclear whether other animals actually think about their own proportions in the same way that we do.
SC: Yeah. Like if you think about when you're driving, you're like, I can squeeze through there. I can't squeeze through there. My car can fit in that parking space. My car can't fit in that car... You have this awareness and it is learned for us all as well as embodied.
DG: That's right.
SC: They're gonna study this in cats, but we know that that's not easy to do. So it was done in dogs first. Let's talk about the dog experiment, then we'll go over to cats.
DG: Always done in dogs first, because in this experiment or this type of experiment, as with many others, you can just bring dogs into the lab. They're pretty happy to participate. So what they did with dogs, and this was done in Budapest, was that they brought a bunch of dogs into the lab, various shapes and sizes, and they brought them into this room. They bifurcated the room with this large wooden panel that the dogs couldn't get past. And there was a rectangular opening in the panel that the researchers could adjust.
DG: And what they found was that when the opening was pretty large and pretty comfortable, the dogs just kind of trotted through, no problem. The owners were on the other side, beckoning them, I think they were calling their name. And when the opening was pretty large, or at least fairly comfortable for the dogs, the dogs just trotted right through. But as the opening got smaller, the dogs could still theoretically fit through, but the dogs began hesitating, and they stopped before they reached it. And this was the suggestion that, okay, dogs have body size awareness. They know or at least suspect that maybe I'm a little too big to get through this thing.
SC: Yeah, and they don't have a drive to squeeze unless there's a really good reason.
DG: Right, that's right. I mean, you think reuniting with their owners would be a good reason, but it wasn't a good enough reason in this case.
SC: No. All right. So what about cats? I see from the story, they did not bring them into the lab to get them all freaked out.
DG: They did not bring them into the lab. And actually, this is a researcher, Peter Punkrins in Budapest, who's done experiments with cats before, and he's had bad experiences bringing cats to the lab, and the cats sort of escape into the ceiling of the lab. So he's done this cool experiment where he does this pointing gesture and shows that cats can follow a pointing gesture, which is something that dogs can do as well. But chimpanzees can't do. Anyways, he learned his lesson and decided to visit homes instead. Went to about 30 homes and did something similar to what Hasina had done for dogs, except in this case, they used a doorway, used a very thick piece of cardboard that the cats theoretically couldn't get around or jump over. And they had, again, these rectangular-sized openings.
SC: When they got smaller and smaller, and the cats were still interested in the experiments, they stayed and got engaged. Then what did they do? Was it the same as dogs? Did they stop going through after a certain size was reached?
DG: Well, Sarah, we should note that not all the cats were interested in the experiment. In fact, eight dropped out. They just sort of walked away, which no surprise to any cat owner. But of the 30 cats that participated, the team did a couple of things. One thing they did was they left the width of the rectangle pretty comfortable, but they kept reducing the height. At first, just like the dogs, when the opening was pretty large, the cats just kind of went through. This time, the owners were beckoning them on the other side with treats and food.
DG: Cats needed a little bit more motivation than the dogs did. But when the opening got really short, about two-thirds the size of the cat, the cats began hesitating. But unlike the dogs, after they hesitated, they still squeezed through. They still went through. And anybody who's seen a video of a cat squeezing under an actual door, there are these crazy videos. It wasn't quite that extreme.
DG: But at the most extreme, this lot was at the height of the cat. So we're talking like pretty low to the ground. The cats, they hesitated, suggesting that they are thinking about their bodies in that sense. They're going, well, maybe I'm a little too tall for this. And yet, at the end of the day, they said, whatever, I'm still gonna go for this. And they squeezed themselves under the slot.
SC: Okay, so I noticed we're separating the vertical from the horizontal. Was the horizontal different?
DG: The horizontal was different. And so in this case, the researchers kept the height comfortable, but they kept on narrowing the width to the point where this slot was half as wide as the cat's body was. And in this case, there's no hesitation at all. The cats just charged through that thing.
DG: And even humans, even if there's a slot that's pretty narrow and we know we can get through, we slow down, we sort of change our posture, we sort of angle our shoulders a little bit. None of that with the cats. Cats just went, boom, right through these super narrow slots.
SC: Okay, so does that suggest they don't care about their width?
DG: So what it suggests is that cats are only, potentially only thinking about their bodies in certain circumstances. They may be thinking about their bodies when it comes to their height, but maybe not so much with their width.
SC: Is there any idea why that might be?
DG: Well, cats are very flexible. They actually don't have functional collarbones like we do, which means they can really kind of squeeze themselves into these sideways pancakes in a way that a lot of other animals can't. Dogs' bodies are much more rigid, which also may be the reason dogs are thinking a lot more about their dimensions than cats are. Where cats are maybe thinking like, hey, I'm basically like a flexible piece of rubber. And so they are just not thinking about their dimensions in certain circumstances.
SC: What about the fact that dogs are all different sizes? Like there's German Shepherds, there's little tiny teacup poodles. Does that make a difference when it comes to whether or not they'll make a squeeze or try to fit through a space?
DG: No, in the dog study, they used a lot of different breeds, a lot of different sizes. They found no correlation with size. It was how high or wide is the opening in relation to the size of the dog itself. With the cats, as you say, Sarah, there's not as much difference, but they did use different ages of cats. They didn't use any very large cats or any incredibly skinny cats. So there probably wasn't as much variation as they did with the dogs. But there were different sizes of cats used in the study.
SC: So Dave, what's next? Are they gonna figure out if cats know how high they can jump before they try it?
DG: That is a good question. I did not ask, but you know, Sarah, the cool thing about this is when humans think about our body sizes, this is something we start doing at a very young age and it's actually been linked to self-awareness. When little kids start referring to themselves in conversation like, I can do this or I want this is also around the same time that they are aware of their body size. So maybe it's a clue that certainly dogs and maybe cats to a lesser extent are exhibiting some sort of self-awareness, at least in these circumstances.
SC: Okay. So can we use this to cat proof our houses better? So say for example, if you have a new cat and you're keeping it in one room, how wide can I open the door before he'll squeeze out?
DG: And I was thinking the same thing 'cause I live in this 11 story apartment in New York. We have these big windows that we can sort of open to, you know, certain apertures. They seem narrow enough that the cat can't get through and I'll open it. When the weather's nice outside. Now after reporting this story, I'm a little concerned that like, have I been keeping it narrow enough, you know, are my cats sort of gonna go for it in a way that I didn't think they might.
SC: You can't just look at their whiskers.
DG: You can't just look at the whiskers.
SC: Thank you so much, David. It's always fun to talk about cats.
DG: Thanks, Sarah.
SC: David Grimm is the online news editor for Science. You can find a link to the story we discussed at science.org/podcast. And I'm hoping at least links to videos of cats doing amazing things on the internet.
DG: Of course, there will be links to videos. Yes.
SC: Don't touch that dial. Next up, researcher Ted Schultz discusses when ants became fungus farmers.
SC: Humans certainly have a reputation for our agricultural prowess, but we're not the only animals on this planet who have learned to farm for food. In the Americas, more than 240 species of ant subsist on fungus grown in carefully cultivated gardens. Some ants, such as leafcutter ants in South America, have even domesticated their preferred fungi, leading to a mutually beneficial arrangement where one species can't survive without the other. But how this symbiosis first began and why has remained a mystery.
SC: This week in science, Ted Schultz and colleagues wrote about how two massive shifts in Earth's climate may have set the scene for early fungus ant agriculture. Hi, Ted. Welcome to the Science Podcast.
Ted Schultz: Thanks. It's great to be here.
SC: So, I wanna start off with just some basics. What exactly does it mean that some species of ants farm fungi? How does fungus ant agriculture work?
TS: As you said, there's 247 species that do this. And what they do is they maintain fungus gardens. They go out, they forage for substrate on which the fungus grows. They come back and they plant fungus on that substrate. Their main, or in some cases, only diet is the fungus. They can't survive without the gardens. And so, when a daughter queen flies off to mate and start a new colony, she carries a bit of her mother's fungus garden in a special pouch in her mouth to use as the starting seed for her new garden.
SC: What kind of information have we been missing up to this point about how this relationship began between these two very different sets of organisms?
TS: One of the most glaring problems in the ant-fungus agriculture world was that although over the past 20 years we've gotten a pretty good idea of ant phylogeny, the evolutionary tree for the fungus farming ants, the evolutionary tree for the fungi that they cultivate has just lagged behind entomological phylogenetics. And the genetic markers available for reconstructing fungal phylogeny were until recently just not very informative. And then in addition to that, to get a nice evolutionary tree that tells you not only how all the different species that the ants are cultivating are related to each other, but that shows you what non-cultivated fungal species are closely related, there just wasn't enough sampling of fungi in the vicinity of the ant-cultivated fungi, so we had a double problem of poor genetic markers and not enough sampling.
SC: So your team looked at the genomes of more than 276 ant species and 475 fungi to help develop this evolutionary family tree that joins the two different sets of organisms here. Once you had these evolutionary trees in hand, what was the next step here?
TS: Then we had to take the two phylogenies, the ant and fungal phylogenies, and look for correspondences across them. And in addition, we created evolutionary trees that are known as chronograms that are dated. And so we could look for correspondences in the origins of major groups of fungi on the fungal phylogeny and the origins of major groups of ants on the ant phylogeny, often a group of ants that cultivates a group of fungi.
SC: Were you able to tell when this ant-fungus agricultural relationship first started?
TS: This was very surprising to us. In general, it's easier to date the origin of fungus farming on the ant phylogeny because you've got all these ants that don't cultivate fungi, and then at the end of one of the branches in the phylogeny, all the ants descended from that branch cultivate fungi. So we know it occurred on that branch.
TS: The branch isn't particularly long, it doesn't span a huge amount of evolutionary time. And so when we use our dating techniques, the centroid of the origin of that branch is centered on 66 million years. You know, 66 million years ago, dinosaurs were around, there were quite a few mammals around, but they were kind of a minor group compared to the dinosaurs. And then all of a sudden, as most people know, a huge bolide hit the earth and caused all kinds of cataclysms and extinctions.
SC: By bolide, you mean the meteor.
TS: Yes.
SC: The famous meteor.
TS: Yes. The ensuing so-called nuclear winter shut down photosynthesis across the planet for what was probably a number of years. And that was long enough to make a lot of plants go extinct, to make a lot of animals that depend on plants go extinct, and of course the dinosaurs to go entirely extinct. But it will also, at the same time... It was a catastrophe for many groups of organisms, but it turns out it was beneficial for other groups of organisms. Fungi that decompose plant material had a heyday.
SC: Okay, so this meteor hits earth, it suddenly becomes very difficult to do photosynthesis on the surface, so these fungi are thriving. How did the ants take advantage of this?
TS: So we also have evidence that ants and fungi were pre-adapted to enter into the tight evolutionary relationship we now see in fungus-farming ants. So in the fungi, what preceded being cultivated by ants was a looser association with ants. And we actually had some evidence of this in one of my many trips to the neotropics. I was peeling apart the leaf litter, and I noticed a species of non-fungus-farming ant that is fairly closely related to fungus-farming ants. I uncovered a nest of it between two rotting leaves, and the ants had built a little wall all around their colony, which is something ants often do. And that wall was interlaced with fungal hyphae.
TS: And had I seen that 30 years ago, I might have just overlooked it. But 35 years of thinking about this stuff made me realize, I wanna know what that fungus is. We were able to sequence that fungus, and it's one of the fungi that is cultivated by ants. So this, in my mind supports the idea that some of these fungi were pre-adapted... They have loose associations with non-fungus-farming ants as well as with fungus-farming ants. And also the dating on the tree and a number of other details suggest to us that there was a long period of loose association between ants and fungi that even may have included ants eating fungi occasionally but not being totally dependent on them, that preceded the end of Cretaceous events. So when that meteor hit the Earth, photosynthesis shut down, lots of plants died, there was a huge amount of leaf litter, rotting plant material, and rotting just means the leaves are being eaten by bacteria and fungi.
TS: And the ants had no other options. I think this promoted a much tighter association between the ants and fungi, and full-blown agriculture arose presumably fairly rapidly.
SC: That is absolutely fascinating, 'cause I can see where the ants are benefiting from this food source, given that there was not as much available to them post-meteor. But what happens in this second time point around 27 million years ago?
TS: There's a lot of fungi that are cultivated by ants. They're in two different unrelated groups, but within each of those groups they're very closely related. And in the group we call Clade I, around 27 million years ago, a group of fungi arose that we call the higher fungi, and we call the association between the ants that cultivate those higher fungi higher agriculture. I mentioned earlier that we know some fungi can be cultivated by ants, or they can just live in the wild without ants. That is not true of the higher fungi. They are always found associated with ants.
TS: They make specialized food bodies called gongylidia that the ants preferentially harvest and eat, and it's been shown that they contain all kinds of nutrients and enzymes that are useful to the ants in their gardens and nutritionally. So we have described the higher fungi as being domesticated. And when we look at this branch, the ants that cultivate the higher fungi are a monophyletic group. They're all descended from a common ancestor.
TS: The higher fungi are a monophyletic group. They're all descended from a common ancestor. What we also know now, due to this study, is there was a whole lot of directional natural selection pushing things in a completely new way on that branch leading to the higher fungi. So obviously something very significant happened there, and when we look at what was happening in Earth history, we can see that this was after something that's called the Terminal Eocene Event.
TS: That was a period of global cooling that resulted all over the world in the spread of dry habitats, and in South America in particular, of woody dry habitats and grasslands. These habitats broke up what was previously continuous wet forest. And it seems to us that it's possible that as the fungus-farming ants adapted to these drier conditions in these drier habitats, and they carried their non-domesticated fungi with them, this resulted in the fungi losing contact with their gene pools of wet forest-dwelling fungi and triggered domestication, basically total dependence on their ant farmers.
TS: And this has analogies in human agriculture. Humans have frequently carried their cultivars away from their places of origin, isolating them from those gene pools, and it's made it easier for humans to practice artificial selection, even unconscious artificial selection, on their cultivars once they've been sort of separated from their continuous wild gene pools.
SC: Thinking about how long ago, 66 million years, 27 million years ago, how confident can we be that these specific events are really what caused these changes in the chronology and the evolutionary tree of these organisms that you were looking at?
TS: The problem with the kind of work I do, which involves a lot of circumstantial evidence and inference going back, as you say, over vast periods of time, is that it's very difficult to establish cause and effect. On the other hand, it gives us a hypothesis that we can test further.
SC: So, with all of this new information, how does this timeline help us understand perhaps other types of non-human agriculture?
TS: There are quite a few types of non-human agriculture, including, maybe most importantly, the fungus-farming termites, which have a lot in common with fungus-farming ants, and which only occur in the old world, and fungus-farming ants only occur in the new world. So, we call all of this agriculture, and to some extent, they have differences. And I think we should include humans in this, too. To the extent that there are similarities, I think it can tell us something about the general rules of what it takes to grow your own food. How growing your own food can evolve.
SC: Thank you so much for sharing this work with our listeners. I really appreciate you taking the time.
TS: It's been great.
SC: Ted Schultz is a research entomologist at the Smithsonian Institution. Be sure to read the paper from Schultz and his colleagues in science this week. It's titled, The Co-Evolution of fungus ant Agriculture. You can find a link at science.org/podcast.
SC: And that concludes this edition of the Science Podcast. If you have any comments or suggestions, write to us at sciencepodcast@aaas.org . To find us on podcasting apps, search for Science Magazine. Or you can listen on our website, science.org/podcast. This show was edited by me, Sarah Crespi, and Kevin MacLean. Special thanks to Ariana Remmel for all the wonderful ant and fungus facts this week. We had production help from Megan Tuck at Podigy. Our music is by Jeffrey Cook and Nguyen Quy Nguyen. On behalf of science and its publisher, AAAS, thanks for joining us.