Science Friday - Snakes Are Evolutionary Superstars | Whale Song Is All In The Larynx

Episode Date: March 5, 2024

In the trees, through the water, and under the dirt: Snakes evolve faster than their lizard relatives, allowing them to occupy diverse niches. Also, researchers are working to understand just how baleen whales are able to produce their haunting songs.Snakes Are Evolutionary SuperstarsLove ‘em or hate ‘em, new research shows that snakes deserve our recognition as evolutionary superstars. The study, published last week in the journal Science, found that snakes evolve faster than other reptiles, allowing them to thrive in a wide range of environments.It shouldn’t be too surprising: Many of the nearly 4,000 snake species occupy extremely specialized niches in their ecosystems. The blunt-headed tree snake, for example, eats through batches of treefrog eggs in Central and South America. Pythons, which can grow to 20 feet long, can take down large mammals like antelopes.Joining Ira to talk about the evolutionary speed of snakes is study co-author Dr. Daniel Rabosky, evolutionary biologist and curator of the Museum of Zoology at the University of Michigan.Whale Song Is All In The LarynxWhale songs can be both beautiful and haunting. But the exact mechanism that the 16 species of baleen whales, like humpback and minke whales, use to make those noises hasn’t been well understood. The finer points of whale anatomy are hard to study, in part because the soft tissues of beached whales often begin to decompose before researchers can preserve and study them. And until the relatively recent advent of monitoring tags that can be attached to individual whales, it’s been hard to associate a given underwater sound with any specific whale.For a recent study, published in the journal Nature, researchers took advantage of several well-preserved beached whales to investigate the mysteries of the baleen whale larynx and its role in whale song. Dr. Coen Elemans of the University of Southern Denmark joins Ira to discuss the work, which included a MacGyveresque contraption involving party balloons and exercise bands that blew air at controlled pressures through preserved whale larynx tissues. The researchers found that there are limits to both the frequencies these whales can produce, and the depths at which they are physically able to sing.Transcripts for each segment will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

What's going on in a whale's throat that allows it to sing? It's Tuesday, March 5th. Politics folks call it super Tuesday. But we say it's Science Friday. I'm SciFry producer Charles Burgquist. Coming up, we'll talk about research into the larynx of baleen whales, like humpback and minky whales, and how researchers MacGyvered a device using party balloons and exercise bands

to explore its frequencies. But first, why snakes deserve a recognition as evolutionary superstars. Here's Ira Flato. Ever since those reported events in the Garden of Eden, snakes have been given a bad rap. Love them or hate them. Turns out that snakes are some of the most evolutionarily elite creatures on the planet.

And it's not just me who's saying this. A new study in the journal Science finds that snakes evolve faster than other groups of lizards. Yeah, and their ability to adapt to hyper-specific diets and circumstances make them winners among vertebrates. So what do you think about snakes now? Well, joining me to share the Science of Serpents is its senior author Daniel Roboski, evolutionary biologist and curator at the Museum of Zoology, University of Michigan,

based in Ann Arbor. Welcome to Science Friday. Thanks so much for having me, Ira. I want to get right into this. Why are snakes such an evolutionary powerhouse? You know, that's a really good question. Why are snakes such a powerhouse? I think that, you know, first, it's not immediately obvious to maybe a lot of folks just how different snakes are within reptiles. But, you know, you look at a variety of traits and you can see this really profound shift between other groups of lizards and snakes. And that's something that, you know, one of the things that we document in our study that really carries through to numerous aspects of their ways of life and their structure. So obviously, yes, this raises this big question of why. And in some ways, we set out to answer the question about this evolutionary shifts and sort of what drives these kinds of evolutionary differences in what different groups of lizards do. And part of our answer that we find is that snakes are simply doing things faster.

Their sort of evolutionary engine is running hotter. What do you mean by that? Give me an example. How do we know that? That's a great question. So we know this because one of the things that we are able to do in our study, for example, and within sort of modern evolutionary biology more generally, is take some of these types of data that are, that we can get from genomes, for example, and from ecological data,

like what things eat. And we can, we can use statistical methods to figure out how fast things are evolving with respect to those kinds of features, like the shape of their skull or the things that they eat. So we can tell you quantitatively that snakes, for example, are evolving new kinds of, you know, a given lineage of snake is evolving essentially faster, is exploring this diet landscape of potential dietary items more rapidly than the average lizard, for example. Wow. And so, you know, the sort of statistics of it gets a little technical, but that's sort of the basic idea.

Do you say there are legless lizards that may look a lot like snakes to the untrained eye, but they're totally different? That is correct. So there are a number of sort of fine. anatomical differences that separate snakes out as a group within the lizards. But there are many groups of lizards that superficially are snake-like. And so I could pick many examples of lizards that have evolutionarily lost their legs where I could hand them to someone and say, like, is this a snake or a lizard?

And people would be like, you know, it's a snake. But actually, it's a lizard and it's distinct from snakes. Now, one of the interesting things that we find in our study is that when these other groups of lizards evolve on this snake-like trajectory, so they essentially discard their limbs. You might say, well, there's something about being a long, legless thing that sort of predisposes you to maybe evolving faster or specializing in the kinds of dietary things that snakes do. And that's really not what we see at all. For the most part, the lizard groups that lose their legs, other than snakes, have essentially stayed lizard-like. And so it's a really remarkable that the things that have gone down this snake

trajectory haven't done what snakes have done, which raises other questions about why. So, you know, the other ones are essentially still specializing on the kinds of foods that typical lizards would specialize on, or they're not doing the same, they're not using as diverse of habitats. You know, they're living a burrowing type lifestyle, for example, more often than not. So where do snakes have, so to speak, a leg up on lizards? In what sense, the snakes have a leg up on lizards? Well, you know, what do we mean by a leg up? So in one sense, snakes have been tremendously successful. Of course, you know, lizards have been hanging around for a long time as well. Where snakes have really have really shined, though, is in terms of their ability to become

ecologically diverse, especially over the past 65 million years or so. There are a lot of species of lizards, of course, but I think snakes have managed to exploit a broader range of habitats on the surface of the earth and a broader range of ecological ways of life and dietary diversities, diverse dietary strategies and so on. And so I think that, you know, one of the things that has set snakes up for in the last 65 million years is it's sort of an ability to take advantage of certain types of opportunities that have happened in Earth history. And one of the things that we see, as we see a signal of after, for example, probably in the

wake of the mass extinction that wiped out the non-avian dinosaurs. is sort of a flourishing of snake diversity that sort of kicked off into 10 million years or so after that. That's a pretty strong signal that shows up in the snake record. And I do think that it might have something to do with that sort of underlying evolutionary speed or that evolutionary potential that snakes have that essentially has let them take advantage of new environmental or ecological opportunities or if you want to think about them as sort of empty ecological niches. Give us a couple of examples of snakes that develop specific niches in their diets.

There are, I mean, the catalog is vast here. I will list a few of, you know, give you a few of my favorite examples. I think that, you know, one of the things about snakes that really separates them from lizards and something that we show, I think, well in our study is that snakes are much more dietarily specialized than the average lizard. And so one of the things that you see within snakes are these incredibly interesting dietary strategies. For example, there are species of snakes that specialize on feeding on essentially these soft-bodied mullusks like snails and slugs that live in trees and they're defended by these heavy mucous secretions. And these snakes have a number of specialized adaptations to feed on these things. And that for the most part will be the primary diet

of those species. Or there are species of snakes that are sea snakes that have these, you know, long paddle-shaped tails and they can dive down into coral reefs. And they are specialists on things like fish eggs. So they just probe through crevices in, coral reefs and look for fish eggs and essentially scrape them off that coral structure down there. There are species of snakes that are, there are many species of snakes that are specialized predators of other snakes. So they are specialist hunters of other species of snakes. So the list sort of goes on and on. There are species of snakes that specialize only on feeding on larval termites. There are some groups, them species that tend to feed quite a bit on tree frog

eggs. And there's some interesting issues there with tree frog eggs essentially evolving the ability to sense when a snake is eating them and starting, and they will hatch when they sense a snake starting to eat their little clutch of eggs. This kind of remarkable behavior that happens in tropical rainforest frogs. You just blew my mind on that one. Wow. How were you able to investigate these interesting dietary habits of snakes? I mean, did you just hang around and watch them? That is a good question. So how do we get all this dietary information on snakes and lizards? So it turns out that for the vast majority of species of snakes and lizards, there are virtually

no or very few observations of these animals doing their thing feeding in nature. They're very cryptic. They're very camouflaged. They live in parts of the world that are hard to get to. And so as a result, we're very information poor about what these animals do in nature. And so what we exploited in our study is this spectacular resource in the form of of our natural history specimens or specimens in our natural history museums where there might be thousands of preserved snake or lizard specimens come from a variety of sources. And you might

imagine that these things have within their stomachs a sort of record of what they've been eating. So we were able to go to this vast sort of, you know, storehouse of natural history specimens and look inside their guts essentially and figure out what these things were eating. And I would add that that's really the only way that we have about what a lot of animals are doing ecologically in terms of diet in nature. So it's a really important source of insight into what animals do in the wild that frankly is very difficult to get in the wild through what you might think of as just going out and observing nature. Is it possible to watch today snake evolution as it happens quickly? And I'm thinking specifically as we have our climate crisis and things are

warming up, getting wetter, getting drier. Can we watch snakes evolve in our lifespan? I would give two parts of an answer to that. First, I would say absolutely that we can see snakes evolving. In fact, we can, we can see lots of things evolving in real time, pretty much everywhere we look when we take the time to do a careful study of it, we see evolution unfolding in real time within populations. But however, I would caution that it's really difficult to go beyond that to make any kind of projections about whether snakes could, I'd to the pace of change in the world around us today. I would say that you're sort of looking at very different timescales in terms of rate of evolution. We're measuring things that are happening

in our study over things that are happening over millions of years. And right here, we're changing things in the space of, you know, decades. So it's just not the same sort of time scale. I would be very cautious about making any projections. I think that I think that I would not read into that as saying that snakes are going to be able to manage, you know, some of these types of environmental changes. Has your admiration for snakes increased as you study them? Well, I don't know. My admiration was pretty high going into this. So I think I have a newfound appreciation for some dimensions of snake biology that I would not have, you know, maybe been aware of prior to starting this. I would add to that, we have tremendous areas of the snake or the lizard, snake and lizard

tree of life that are very data deficient. where we have very little information about the basic biology of these animals in nature. And so, well, it seems like we have a lot of data in our paper. And in fact, we do at the same time, it's really clear when you sort of look at where those, the data are, you know, across the surface of the earth, that we have like diet data for like 15% of species. That dating that data is like a was a lifetime of work for many, many researchers. And we're in a world where we're changing climate very quickly.

And we don't have the most basic information about many species of lizards and snakes and many other things too. And I do think that in, you know, 10 years, 20 years, 50 years down the road, we are really going to regret that we did not go all out at collecting some of these information because a lot of these populations and many of these species, unfortunately, are not even going to be with us. And we're going to have little understanding of what roles they're applying within their systems. Well, Daniel, I've learned so much about snakes today. I want to thank you for taking time to be with us. Thanks so much for having me on the show. Great stuff. Daniel Roboski, evolutionary biologist curator at the Museum of Zoology

that's at the University of Michigan and famous Ann Arbor. If you've heard recordings of whale songs, you know that they can be both beautiful and haunting. Really cool. You know what? The way that baleen whales like humpback and

Mickey whales, the exact mechanisms whales used to make those noises, we really never understood. That is, as they say, until now. A recent study in the journal Nature investigates the mysteries of the whale larynx and its role in whale songs. Joining me to talk about it is Dr. Cohen-Eleman's. He's a professor of bioacoustics and animal behavior at the University of Southern Denmark in Odense, Denmark. Welcome back to Science Friday.

Thanks so much for having me again. It's always a pleasure. It's so nice of you to say that. Okay, you know, it's amazing to me that we didn't know how whales made those sounds. Why is that? Well, it's difficult for several reasons. So first of all, if you put a microphone or like an underwater microphone, which is called a hydrophone in the water, you pick up sounds from very far away because sound travels so fast and so far in water. And so it's actually quite difficult to say if you're recording something that it is a certain animal that is in the area because you see it. It could come from 10 miles away or even further. Since the last 20 years or so, people started to develop tags you can put on a whale. and since then it becomes easier to actually associate a certain sound with a specific species.

So that's one thing. The other thing is that it's very hard to study physiology of whales. So first we've hunted them down to near extinction, so they're all protected now. And the other thing, when there is a whale that, for example, beaches and dies, then they typically rot so fast when they're on the beach because you cannot get there fast enough, for example, that actually the tissue is so rotten, you cannot see so much from it, or you cannot learn so much from it in terms of physiology. Well, then, what made it possible for you to study them now?

So we were extremely lucky that we have a very active stranding network in Denmark and also in Scotland, where basically people alerted us to a whale that beached. This is the first one was in 2018, actually. And it beached in very bad conditions for the whale, of course, but in very good conditions for us, close to a harbor, very cold weather, cold water. And so we could get there very fast and get very fresh tissues out. So you were able to look at the larynx of these beached whales. How similar is a giant whale throat to mine or yours?

Well, it's quite different. And that was partly known because people have studied the anatomy for whales for quite a long time and also the larynx. What is very different is that the little cartilage is that move our vocal folds together and as such a loud speech, they are very different in a whale. They've become massive tubes that basically form a U-Shed. shape. And this U shape is largely immobile. And we think that's the case because then it opens the airwaves when these animals have to breathe on the surface. So you have massive flows, airflows coming back and forth when they surface and breathe. And if you then have vocal folds sitting in the way, they would start to flap and actually be annoying. You don't want that. But they're underwater and they

make these sounds, which means they still have to blow air through their larynx. How do they do that? Yeah. So what we think is that what they do is they still push air from. their lungs through their larynx, and this goes into a sac, that's called the laryngeal sac. And this sack collects all the air, and then a big muscle surrounding it pushes it basically back through the larynx, back to the lungs. And this way they can recycle the same air back and forth without surfacing and actually taking a new fresh breath. Now, you're talking about the baleen whales, right?

Do the other kinds of whales that don't have the baleen in them? Do they do the same thing? No. So actually last year, we had a paper where we showed. showed how the tooth whales, and that involves the dolphins, the killer whales, and for example, sperm whales, how they make their sounds. And they evolved completely novel structures that sit in their nose. And so they've made a totally different solution to this problem. How do you make sound on the water when you hold your breath? Wow. Okay. So let's talk about the whale

that washed up that you used. How do you go about proving with a dead whale that this is how it makes the sounds? Tell me about your setup. Yeah. So first we started the analysis. anatomy in great detail. We froze these larynches down. We study their anatomy. And then we build a setup where we can basically in very controlled conditions can blow air through the larynx. And that's where you can study the vibrating structures that generate sound. Now, and if the tissue is fresh, then actually the properties are very similar to in a living whale. And that means that if you get vibrations, they should be the same as what the whale does in vivo. And that's where we also saw. So it took a while to build such a setup because it's not because it's big, but because it acquired all kinds of adaptations because the larynges are so huge. And we could measure very accurately things like flow and pressure. And with high-speed cameras, we could film things that vibrate. And we could show that the vibrations were exactly the same frequency as you see in the living well. Well, you got to tell me how you MacGyvered this thing. Yeah. So it was a nice crossover between McGiver and scientific research. So we needed a setup where we have very high flows of air with

low pressure. And that's actually, that was a bit complicated. So we ended up using, first we wanted to try weather balloons. That didn't work. And then in the end, we used a party balloons, basically, that have a really big volume and a very low pressure. And then we could let the air out of these things while measuring pressure and flow very accurately. And that powered very accurately the loranges. Wow. So you had a really close, accurate sound of how the living whales would do it. Yes. So what we can mimic really accurately is sort of the lowest, frequencies these animals can make because then the tissues are not so stiff and they vibrate at those lowest frequency.

What we couldn't do in the lab was to then activate muscles, for example, because the tissue is dead. Right. And to do that, we made computational models where we basically made a full 3D larynx in the computer, could blow air past it, confirm our first experiments, but then we can also start simulating the activity of muscles, for example. So with these computational models, we could now show how high, for frequency sounds you could generate with this mechanism.

Okay, lucky for us you have provided us with some of the sounds you created. So let's listen. Wow, Dr. Ellumans, what are we listening to? What are we hearing? So what we're listening to is actually the acceleration of a part of the vibrating tissue. So it's made into sound. That was really low frequency, wasn't it? It's very low frequency, yes.

And that's realistic. Totally, yeah, yeah. So this was of a sigh whale. And the cybal makes these very low frequency, um, sweeps. And that's exactly, basically,

what these animals do. And of course, the whales often have these sounds in the very high, higher part, the higher registers. Does your research account for these two? Yeah,

so partially. So all these baleen whales, all 16 species, make very low frequency sounds. And if we look in detail at the anatomy that is studied in these animals, we see that this cushion, where we show now that generates the sound,

is there, is present in all these species. So we think that's the ancestral state. But a few species, like the well-known humback, but also bowhead whales, for example, they're very well-known for their song, and that's very high frequency. And so how do they do that? And what we now found is that actually the erythnoid cartilage is this big U-shape in these species is able, again, to come together.

And so it, again, looks a little bit like human vocal folds. And that makes, again, definitely sound. And we think that mechanism is responsible for these very high frequencies in those. species. That we were not able to show because we couldn't simulate that in the lab. I see. Of course, there is a big variation in the human vocal range. You've got James Earl Jones on one side and you have an opera soprano on the other. Do whales have a similar range like that? Well, actually, I wouldn't know. We don't know enough yet about how individuals perform. So we have tagged individuals and can see what they can do. But there's lots of mysteries out there. I talked to a

colleague last week. And for example, a few of the whale species seem to go lower and lower and lower in frequency over the last years. And everybody's really puzzled how this could work. And so there's lots of open questions there. Hmm. Your research says that there are some sort of limits on how and where whales can sing. Is that correct? Yes. So we show now that this U shape against the cushion mechanism is limited in frequency range. So first, it's really cool because it allowed the whales to make sound while holding their breath on the water. And it allowed them to live, basically, and evolve. But it also is very limited, and it limits them to probably frequency of, let's say, 5 hertz to 300 hertz. So that's one limit. Another limit is that we

could now measure how much air they need actually to make these vocalizations. And because we can estimate the amount of air available in a whale, and also scaling with size and so on, we could estimate how deep can you now take basically this system and still have enough volume to make a sound. When we did these simple models, it basically showed that about a hundred meters or so, deeper than that, the whales, they don't have enough air to basically make sound. So there is a frequency range and also a depth range where these animals are able to make sound. It depends on how long the vocalization is, but we estimate at about 100 meters, this doesn't work anymore.

That's not far down, is it? It is for us, it's very far down, but for a whale, it's really not. It's really the surface of the ocean, and a lot of whales can dive much deeper. But so we really now give a constraint that the vocalizations are mostly restrained to the surface. So when they want to talk to each other or vocalize, they have to come closer to the surface to do that. Yes, and that's also actually that's that we predict. And that's also consistent with the data that people are getting from these tags, where you put a tag on a whale. Right.

And those animals typically sing below 20 meters, actually, or even shallower. And what about boat noise? Does that overlap with the sounds the whales are making? Yes, absolutely. Actually, the recording you just played of this whale in the lab really reminds you of a boat, right? And that's also one of the big problems. So now that range we show where the animals are able to communicate is exactly or like very tightly overlapping with the range where we make most noise on the water or a lot of noise on the water and particularly shipping noise. So they can't sing higher to be heard over the boats then?

There is limitations, physiological limitations. to how loud you can sing, basically. That's one. And now we also show there's a limitation to the frequency range and the depth. So all these three together limits our physiological limitations to these animals. Okay, so tell me, as I wrap up here,

tell me what more do you want to know about this? Well, one thing that's really open still is how the humbacks, like male and also female humbacks, make these very high frequency sounds. That would be really fun to figure out. Well, I want to thank you for coming back and keeping us informed about whales.

Thank you so much. Stay care. It's always a pleasure to talk to you. Cohen Elements is Professor of Biocoustics and Animal Behavior at the University of Southern Denmark in Odense, Denmark. That's it for today. Lots of folks help make the show happen, including John Dan Koski, Kathleen Davis,

Dee Petersmith, Robin Kasmur, and many more. Tomorrow, a conversation with a young researcher studying Parkinson's disease. I'm SciFri producer Charles Berk. Thanks for listening. We'll see you soon.