Why seals don’t drown, and tracking bird poop as it enters the sea
39:13 Share

This is the Science Podcast for March 21st, 2025. I'm Sarah Crespi. First this week, newsletter editor Christy Wilcox. She's here to discuss stories from the sea. We'll talk about seabirds' contribution to ocean nutrients, new organisms from the Mariana Trench, and how males of the extremely venomous blue-lined octopus use their toxins on females.

Next on the show, researcher Chris McKnight talks about testing free-living seals to see how they respond to different carbon dioxide or oxygen levels in the air. It turns out they don't act like other mammals, which go into a panic with high carbon dioxide. Instead, seals appear to directly detect oxygen, which could be a safer bet when your life is mostly spent diving deep underwater.

Now we have Christy Wilcox. She's the editor for our daily newsletter, Science Advisor. She's brought a trio of ocean or marine stories. Hi, Christy. Welcome back to the podcast. Hi, Sarah. Thanks for having me again. Sure. So let's dive right in. I think we should start with the venomous octopus story. I know, I know this is the one that you care the most about.

I mean, I did write a whole book on venomous critters. So yeah, I am a big fan. Okay. And this is the super scary. If you're a person who likes to go tide pooling off of Australia, this is a scary octopus. It's a blue lined octopus and it has a pretty famous venom on board, right?

Yes, yes. So it's one of the four species that we consider to be blue-ringed octopuses. They all have an incredibly potent paralytic in their venom called tetrodotoxin. It's the same stuff that you see in pufferfish. It is...

It is a super nasty little molecule that a bite from one of these guys. And keep in mind, these octopuses, they are literally the size of a golf ball at biggest. I mean, they are teeny. They are little. They are wee. But one bite is enough to kill a person. And indeed, it has happened in the past. These octopus have killed people. So, you know, if you ever see a tiny little octopus with lots of little blue marks on its body, don't touch it. Don't pick it up. Yeah.

And tetrahydrotoxin is famous because it blocks sodium channels. Super important for conduction in your nervous system, which is a really cool research story all on its own. Yes, it just basically completely shuts down your nerves throughout your body. A little, little guy with a really potent toxin. They're little, they're wee, they're fragile.

They want to eat something like a crab that has this hard, tough shell and is really, you know, strong and could rip them to shreds. What they do is they take a bite, you know, inject this paralytic, paralyze their prey, and then they eat it. But researchers watched pairs of these octopuses mate and how they do their sort of courtship and mating ritual. And what they found is that the males, which are about 100%,

a third of the size of the females. So they're much smaller than the females. The males will climb on top of a female and then bite her, aiming for her aorta, that major blood vessel that allows the blood flow through the body. And they will inject their venom. And the females, once they have been bitten, they go pale. Breathing slows down really slow. And

When the researchers actually shined the lights in their eyes, their pupils didn't react. So they are getting actively paralyzed by this tetrodotoxin. Are they like other animals where males are at risk when they go to breed with a larger female? That is what the researchers posit is happening here, is that these males are trying to avoid being eaten. Because what happens in octopuses in general is that the females, once they mate and they lay their eggs, they don't eat.

ever again. They're done. They're going to live out the rest of their lives, taking care of those eggs, trying to make sure as many of them hatch and that's it. So they need to have really good reserves of energy before that moment, before they stop eating. And so up until that point, anything they can eat, they're going to want to try to eat. They're really hungry. They're really hungry. Right up until mating. And

If you've got a little male there, that's moot that one could have a final meal of before laying your eggs, right? It's a last chance to snack on something before going into reproduction mode. But it is to the species advantage. It's evolutionarily advantageous for the male to survive reproduction, right? Well, what's really interesting about it, though, is that

Not only do the females die after reproducing, so do the males. In most species of octopus, and that's like what people think happens in these males. So why are they trying to avoid being eaten? Other species like spiders, this sexual cannibalism is really common in spiders. You have a big female, you have little males, and they've actually evolved strategies of

of self-sacrifice where it's like, they'll be like, all right, here, eat my body as long as I get my sperm in. I'll give you a nuptial gift. I'll give you extra food.

you can take my body, you can eat this extra food. I don't care. Just make sure that I get to have the babies, you know? Does the female even have a chance to eat the male if he's paralyzed her, mated, and then? Well, no. The idea is that this paralyzing strategy is to make it so that she doesn't eat him and so that he can escape. But why he wants to escape is the question. Or maybe he doesn't really care about escaping. What's possible is that

it takes a certain amount of time for these males to deliver their sperm. And so these copulations, they said, run about 30 minutes to an hour where he's taking his specialized sperm delivery arm and he's inserting it into a reproductive tract and he's handing over his sperm. And so one possibility is that that process takes so long that

the males are worried about being eaten before they're done. Right. Yeah. So they might be paralyzing them not to prevent themselves completely from being eaten, but to prevent themselves from being eaten too quickly. Are they giving the female a smaller dose than they would give, say, a prey item? And that's even more interesting because what they did is they looked at the venom glands, which are the salivary glands of these octopuses.

And the females have proportionally smaller venom glands than the males. And so it actually seems like the males might be giving them a lot or a bigger dose than they would normally need for a prey item. And that makes sense because these octopuses are

are probably resistant to their own toxins. I mean, it doesn't do you much good to have tetrodotoxin in your body if it's just going to paralyze you, you know? So they might have evolved these larger glands that hold more tetrodotoxin because they need to overcome that natural resistance level that the female has to the toxin. Fascinating. Oh, that's very cool, Christy. All right, let's talk about another seaworthy tale. This is about

birds above the ocean, actually. So these are birds that deliver nutrients to the ocean. Yes. Well, what I thought was so fascinating about this study that is still currently in preprint under review is that when you think about putting cameras on animals to figure out what they're doing in the wild or to observe their natural behaviors, right? My favorite is the under chin camera on domesticated cats. Yeah.

It's just the most amazing experience to live a day in life of a cat. You're seeing it. It's the animal's point of view. They've done ones like seal cams where they're basically on their heads. Yeah. And so you think about that, like you're like, oh, you're going to put a camera on an animal. You're going to put it facing forward near their head and facing forward. They instead decided to put it underneath their bodies and facing backwards. And there was a very good reason for that. They wanted to

figure out when and where these birds were using the restroom. So excretion, it's an important contributor to the environment. We take stuff in, we let stuff go, we're moving it around, we're enriching it for certain nutrients. So yeah, especially birds. If you think about guano, it has lots of desirable properties, right?

Oh, yeah. I mean, there was wars waged over bird nesting islands because of the rich resources of nitrogen and phosphorus that are in bird guano. It's used as fertilizer. It's used to make explosives. People really, really love this stuff. And so do plants and other creatures. They need nitrogen to build proteins. They need phosphorus to build proteins and other biomolecules that are essential. And so

Understanding where seabirds in particular excrete this guano can help tell you where they are shuffling nutrients around or how nutrients are moving through marine terrestrial interfaces, these colliding systems.

Absolutely. So what birds are we talking about here? We're talking about a kind of bird called a shearwater. They're seabirds and they spend a lot of time out on the ocean. We don't see what they do out in the ocean. We know whether or not they're excreting on land. We see all, you know, you see seabird colonies covered in bird poop. Yeah.

But we don't know whether or not they're doing that at sea as well or to what extent they're doing that at sea. They put these cameras on the birds. And what was really interesting is that the birds, not only did they go at sea, they went while flying almost always, not when landed because they will sit on the sea surface for a while.

And you wonder, why not just go when you're sitting on like a big toilet, right? And so the researchers had some ideas for that. They thought perhaps that the chemicals in that material might attract predators. So, you know, there might be a shark or something lurking down below that might be like, ooh, I smell something at the surface. Like, let me go up and eat it. But the other thing that was just really cool about it is these birds are like wild.

really timely about their bowel movements, if you want to call it that. Oh, yeah. This is so crazy. So they have a regularity that is to be envied. Yes. And it differed between the different birds, the individuals. But each individual, I mean, it was down to the minute. There was one bird that was every 40 minutes, almost exactly to the second. I mean... And what could be a reason for that kind of cycle change?

Do the researchers have any idea about why that would be so regular like that? Why it would be so clockwork? Adding that information to the fact that they do it while flying, one of the ideas that they have is that this is a weight maintenance technique, let's call it. These birds have to fly a lot, right? They've got to be in the air. And the more weight you have, the more you're going to have to carry. It's an energy calculation. It's an energy calculation. And so like if you are regularly moving, not just solid waste, because in birds, it

It's solid and liquid waste combined. They have one hole. It's the cloaca. They got one exit route. So...

you're talking about water weight as well. And so having this regular cycling might be a way of making sure that your body weight doesn't fluctuate too much and sort of conserves energy in that way. All right. Well, I really want to see what other backwards upside down camera work comes out of this now that it's been done on birds. Right. Right. I mean, I'm actually really curious. I mean, they say, does a bear go in the woods? Right. I mean, let's find out. But does it?

go next to a tree or not. Right. Does it go next to a tree? Does it have a strategy? Are they as timely as birds? Who knows? There is definitely a bias about what's coming out versus what's going in, in research, I would say. Yeah. Okay. One last story. This one takes us deep, deep, deep into the ocean. We're talking 10,000 meters down in the Mariana Trench. This is amazing. The

pack of papers that just came out. It's super fascinating. I mean, obviously, we're talking about a place that is very hard for humans to visit. We don't get down there very often. And this is from the Mariana Trench Environment and Ecology Research Project. Three papers came out and they looked at these different aspects, including the diversity of the tiny life that lives down there. Yeah. One of the things that really stood out and that we got lots of comments from

from researchers about is that they found this unbelievable diversity of microorganisms. So these little tiny critters and these little microbes are just

Unbelievably diverse down there doing things that we have no idea yet of what they're doing and how they're doing it. And how they've adapted, right? Right, right. I mean, they found more than 7000 microbial species or something in these samples and almost 90 percent of them were new to science. What do they use to sample this far down under the ocean? So they had this really cool method.

Vehicle, remotely operated vehicle. I am going to butcher the name, but it's something like Fendouzhe, F-E-N-D-O-U-Z-H-E, which one microbiologist described as an engineering marvel because it's just got these robotic arms and this sampling basket and it can collect hundreds of samples every time it goes down.

And so it's bringing back all of this sediment, which is filled with microbes and other tiny critters that live at the bottom of the ocean.

And then they're looking at things like the genomes of these little critters and trying to figure out whether they're different species, whether they're anything we've seen before in deep sea sediments or in sediments, ocean sediments in general. One of the things that was a common theme amongst these new species is that they had really small genomes. It seems like they have sort of genetically streamlined for whatever existence they're eking out in this dark space.

cold place. What are some other adaptations that they found in the Hadal zone? H-A-D-A-L. Hadal zone. This is the deep sea. Yeah. So one of the things they found is that these microbes are living off of substances that we wouldn't be able to live off of. We eat predominantly things like sugar and carbs, and then we break that down and that's our fuel. These creatures are living off of things like carbon monoxide, which is

Not something you think of as the carbon source for an organism. We've talked a lot about tidy guys. Is there any fish down there that they looked at? Yes, yes. So they also found a number of fish species and some really interesting observations about those. One was that any of the fish that they found deeper than three kilometers, they have this genetic mutation that allows their cells to mutate.

turn genes into proteins more efficiently. So that process of transcribing genes and turning them into proteins, ultimately, they're better at it than we are.

And you must think that that must have something to do with just not having as much energy or as much resources down there. And so like scarcity, everything your body does has to do better, you know. But also they were able to kind of look at relatedness of these species to shallower species and try to sort of figure out when they went down. And so, for example, they found the eels seem to have dove down about 100 million years ago.

Which is interesting because around 65 million years ago, you had the major extinction event that wiped out most of the dinosaurs. That was also a pretty bad event in the oceans. It was planet wide, absolutely. And these deep sea eels, they were okay. They probably survived that extinction event in part because they were below where the problems were happening. Oh, very cool. I can't wait to see more research. I'm

Would you ever want to visit? Would you ever want to go deep, deep, deep in the ocean? No, I would have to feel really safe about like the vehicle I was in. But it would be so fascinating to go down that deep and then to be like... I'm a landlubber. No, I'm a landlubber. I don't want to go to space. I don't want to go to the Mariana Trench. Just give me sea level. I'm okay. Give you a nice, calm beach. Yeah.

All right, Christy, anything else you want to mention from the newsletter? I just want to mention in general that everyone should subscribe because we have something new and special every single day. There is exclusive content that you will only find in the newsletter. You will not be able to find it anywhere else on science's platforms. I really love your headlines of all the different articles. It always catches my eye. And, you know, there's always like a gif. There was a gif.

Speaking of excreting, in the past week, it was, what is it, a whale urinating into the ocean? Yes, yes. It was a study that looked at, again, nutrient movement, right? We talk about excretion as nutrient movement, but it was looking at whales and how these large whales, how much nitrogen they're moving from their polar sort of feeding grounds to the tropical placemats.

places where they give birth and hang out where they don't really eat as much. So if you want to see that, subscribe to this newsletter. It perks me up every day to see what headlines you guys have come up with. And there's profiles of people, young researchers. And, you know, one of my favorite sections of the magazine is actually the book section. And it's so good that that's getting more exposure through the newsletter.

Yeah, no, I love hearing about all the cool books and TV shows and things that people are watching and why they liked it. I mean, it is definitely one of my favorite things that we've added. All right, Christy, thanks so much for coming on. I'm sure we'll have you again soon. Thanks for having me, of course. Christy Wilcox is the editor for Science Advisor, our daily newsletter. You can read more or subscribe at science.org slash scienceadvisor.

Stay tuned for a conversation about how gray seals have adapted to spending so much of their lives underwater.

Inhaling air enriched with carbon dioxide causes panic in people and other mammals too, as a general rule. That's because we are able to detect carbon dioxide levels and they're used as an indicator to our bodies that there's not enough oxygen around to sustain us. It's an indirect measure of air quality. This week in science, Chris McKnight and colleagues wrote about how gray seals use a more direct approach and don't even blink at CO2 levels 200 times higher than normal.

Hi, Chris. Welcome to the Science Podcast. Hi, Sarah. Lovely to meet you. Thank you very much for having me on. Sure. I was really excited about these initial facts that are only tangentially related to the seals, but we'll get to the seals. So people don't detect oxygen in their blood, in their lungs directly. We use this proxy of CO2 levels. Why did you think that gray seals might be doing something different? That actually started from humans and a little bit closer related to seals, diving humans.

So I've worked on a few dips and types of our categories of diving peoples, but most of my focus had been on the elite competition free divers. So these amazing athletes that can make dives at a breath hold to, I think the record at the minute is 134 meters. The first time I was there putting instruments on, I observed quite a few blackout.

actually. So basically lose consciousness, something we call hypoxic syncope. And then sort of through discussions in my own learning, realized that it's because, well, one, they primarily rely on CO2 to effectively dictate when they should terminate a dive and the sort of feelings of wanting to breathe again are all driven by CO2. So it's quite an unreliable barometer. It's very clear in that scenario, people were losing consciousness underwater and

And obviously that only happens once without support in a human or an animal. And then that's it. Your fitness drops to an immediate zero over the space of a couple of minutes. So it never really, from that point on, it never really felt that the seals would be like other mammals and be insensitive to O2 and rely on CO2 to make their diving decisions. So it seemed impossible.

to us that there has to be a fundamentally different sensory system or sensory perception, not relying on CO2, but actually relying on what we're very poor at sensing, which is oxygen, because that's the critical gas that sustains, I guess, what we would call the human's consciousness. But let's say the ability of the brain to function that allows you to sort of make decisions and behave. Right. So with the people, what are they doing? Are they overriding their own sense of panic and wanting to breathe? Or are they

expelling a bunch of CO2 at the surface. So they're kind of tricking their bodies into thinking that they have more oxygen than they do. Yes. So I think very often divers will say that they do not hyperventilate. So if you hyperventilate, you artificially, you mechanically reduce your CO2 levels. They say they do not do that, but they do tend to use a breathing technique, which is called lung packing, where they basically fill the lungs until they're sort of

as filled as they'll go. And then basically using the mouth, they force more air down. But in the process of doing that, they do reduce CO2 levels. Now, they say that they rely on the CO2 as a barometer, but because it induces something called involuntary breathing contractions,

where it's effectively that very core autonomic responses, even though they're holding their breath and they won't breathe, the body is making the breathing movements and they basically know the number of them that they can sustain before they will effectively lose consciousness or

lose certainly complete awareness. But that's all CO2 driven. To come back to a different group of people, diving people that I've worked on is indigenous diving people. So people such as the Korean Haenyeo, they've been diving, at least their diving's provenance for at least 3,000 years.

On Jeju? Yes, the Jeju Hanyang divers. And they certainly do not hyperventilate. They seem to be very regulated in their control of CO2 and in sort of discussions and information. Blackout is very, very rare. That's super interesting. So they seem to be much more cautious about balancing CO2 and the importance of CO2 in

in their decision making. But again, CO2 wouldn't be an issue if that's not the key gas that you're sensitive to. If you could perceive the oxygen component in the blood. Yeah, you're just more connected to the actual gases that your body cares about. Exactly. You're not worried about overwhelming yourself with CO2. You're worried about running out of oxygen. And you can see it where humans are trying to mess with it to do their long diving.

But seals have actually, it looks like, kind of overcome this by detecting O2. So this is not an easy thing to test. Like when you're working with people, you can ask them what they do. You can ask them how they feel. You can do measurements on them before and after dyes. But how would you do this with gray seals? What did you do to administer gases to them, for example? Exactly.

Exactly. So the beauty of working on humans is you can present something and go, do you sense that? Do you feel that? Or tell us when you feel a change. For seals, it's much more difficult. And effectively, you have to look at, allow them to make their behavioral decisions based on experiments. So changing the gas in which they could inhale. And we do this in humans. It's not a sort of

completely different experimental setup. It's very common. I mean, even... I mean, it's a little different. It is. Even, you know, sometimes in MRI, they'll deliver some high CO2 gas just to get a delta change in blood flow in the brain. So we effectively, we wanted to carry that paradigm over of basically delivering different gas concentrations. So delivering high oxygen or low oxygen ambient or high CO2, and then allowing the animals basically to

to see how it affected their behavioral decision-making. And so to do that, we at the Sea Mammal Research Unit have something called a short-term captive animal facility, which basically means that we can bring wild seals into our facility for a period of time, and then we release them again back into the wild. And we have a large pool, and in that pool, we have

we call a simulated diving setup. So rather than the animals diving vertically, they dive horizontally. It's like a really large swimming pool. Then we can have them breathing in one place and then diving to take fish, basically a big underwater conveyor belt of fish and then coming back to breathe. So, I mean,

having one place where they breathe and another place where they eat fish is probably one of the most fundamental aspects of being a seal. And then when they're at the surface, we can control the gas that they breathe. So as I said, we would have our ambient, we'd have our CO2. We had CO2 200 times normal levels. I mean, to a human, that would sound very, very high. But these animals, you know, spend some 90% of their time at sea holding their breath. So their CO2 levels are always high.

So we went to 8%.

And then independently of that, we also wanted to look at the oxygen, which was our hypothesis was they can in fact sense it. So whereas we took CO2 up 200 times, we also doubled oxygen. So chemical hyperoxia or we halved oxygen. So we took oxygen to 10%, which is about equivalent to the pressure, partial pressure of oxygen about Everest base camp. So this is not outrageously low. Yeah. I saw the, there's a drawing and illustration in your paper of a little tent.

Yes. The seal can surface underneath. Exactly. And so it's like a, pented against the water. This is brilliant. When I was reading it, I couldn't imagine how you would serve the gas mixtures because I was like, they have snouts? Like, are you going to put a,

No, it's a little transparent tent. Exactly. It's a little pyramid. Bizarrely, when we're training, you know, habituating or familiarizing the animals to it, they really seem to love being in that pyramid. And certainly gray seals, there's like a sort of ice seals. So I mean, they would have been a species that would have been used to basically breathing in a confined space like lots of Arctic animals do. I think...

A lot of people that train animals, whoa, it must be difficult to get them to do that. But I'm like, this is the most natural thing in the world for them. Especially living in Scotland, you know, it's very often rainy and windy. And when they're in there, I mean, it's like being, you know, it's lovely and protected. It's not bothering them at all to get exposed to these different gases. Once you had established these safe levels that were also, you know, the experimental levels that you wanted to test, what did you measure in their behavior in response to those changes?

So we wanted to look at dive time, the length of their dive and all the dives of their own volition. So they decide when they dive, how fast they swim, how many fish they take, how long they spend under, and then they decide how long they spend at the surface. So it's basically how long we are dives and how long was the period at the surface when

When you're breathing, getting rid of CO2 and taking oxygen on. And our hypothesis was that if they can sense O2, if O2 is lower, dive duration should be lower as they effectively, they have less oxygen in their reserves to support dive duration.

dive duration. And if oxygen is higher, we'd expect that their dives would be longer. And then there's a sort of outstanding question of, well, what is high CO2 going to play into this? Right. We already know they're not bothered by high CO2 because they're going in those tents, but it could have an effect if it's not related to cognition, it could affect their dive time. So which conditions gave the longest dives for the seals? It

became quite obvious very quickly when we give them double the normal levels of inhaled oxygen. One animal, she was a great diver. Her name was Trish. She immediately went from dives that were about six to seven minutes. And she just went and did two nine minute dives back to back, took all of the fish and she was done. So I was like, okay, I mean, this starts to make sense. But I would also say the CO2 was incredibly surprising. So you didn't see an impact on their dive times? No. And I mean,

If you were to breathe high O2, which I've tried, the idea of holding your breath at all

is very difficult. Your whole body said, no, we need to get up. We need to breathe. The fact that, you know, very immediately, you know, you're measuring the animals that they just head off down the pool, spend, you know, a couple of minutes taking the fish off the feeder and then swim back and then pop up was really surprising. This is so interesting, this comparison with people. So if you gave a human extra oxygen, but you didn't tamper with the CO2 levels at all,

it wouldn't help them spend more time underwater because all the responses are to the carbon dioxide. Exactly. And I mean, there may be quite a few listeners that have actually had high oxygen. So not infrequently before you have surgery, you put on a face mask, which is basically 100% oxygen. And I mean, when you're breathing that, you have no idea. You have no change in sensation or feeling. But then the other sort of end of the spectrum is, of course, something like carbon monoxide poisoning.

where you just don't detect the reduction in oxygen. So we are very poor. Whereas if you were to take a breath of high CO2, this will happen to some people again in the water. If you have a snorkel, it's too long. Just pools in there, right? You start to get that neat breeze. I can't even go under the covers. I am so sensitive. That's exactly the feeling. And again, to come back to the start of it is that if you sense that gas, it leaves you very fallible.

to that CO2 giving you one wrong reading and then you do low on oxygen, not enough oxygen to support brain function. And as you see, there'll be lots of videos online of freedivers, they call it shallow water blackout, where you'll see that the body just stops moving, they just go limp. Wow. That happens once in an animal, they're removed from the population. So our belief was that evolution would have selected very hard against that, especially in these animals that have gone from a terrestrial ancestor to phytonutrients

full time. You know, the way you like to think of seals is they're not a surface dweller that makes dives. They're an animal that lives underwater and only periodically come to our world to breathe, make the inverse of a dive to come up to our world to take a breath. And there's no way that that really could have been sustained if you have this fallible perception system of a finite gas. So it really sounds like a dolphin. Do we know what dolphins are detecting? No. So there's been a little bit of work in manatee, but very much focused on

the effects that CO2 and O2 have on respiration and heart rate, but not on perception and critical decision making. So no, no idea about dolphins.

But I mean, if I had to hypothesize, I believe the same hypothesis that we made stands for them as well, is that they make the mistake once and run out of oxygen. And, you know, it's game over, especially some of the incredibly deep diving cetaceans, you know, like baked whales on sperm whales. Their room for error is very, very small. So I think we should circle back to this idea of it being cognition because we're using it in this way that's basically saying,

they're making a decision. So if they're at the surface, they decide how long to go. They don't just pop back up because levels are bad, right? Yes, we do know that they do plan dives. And we know that from their changes in the heart rate. We know that as soon as they dive, their heart rate will drop. And the magnitude of that drop is a very good correlate for how long that dive is going to be. So we know that

seals in particularly, especially grey seals actually, are very good at planning their diving. So the idea for us is this cognition and perception. So this is something that happens higher in the brain, in the cerebrum, whereas O2 and CO2 absolutely affect the things that we're out of control of, heart rate, respiration rate. But our feeling was that while there may be an effect there,

It's how those deep brain, the gas sensors, how that information is integrated up to the higher parts of the brain that then allows the animal to say, well, now is my time to cancel that dive. Or now here's my time at the surface to start this dive. Yeah. I'm going to go get all those fish. I'm going to spend nine minutes under this water. Yeah. Yeah.

In that sense, the study, it's actually very simple. It's, you know, if we give you more oxygen, do you dive longer? If we give you less, do you dive less compared with breathing ambient there? But it tells us so much about what's going on with the seals, like sense of the world, right? Exactly. And that's for me and my research. What excites me is how do they see and sense the world? And I mean, I think if you asked...

my goodness, even a sort of three-year-old, you know, tell me about a seal. They'll say they come to the surface and then they dive. So it's so fundamental to what they do. But the risk of doing it wrong is ultimately fatal. Getting a little bit of insight into, well, how do you never make that mistake? It is so simple, but it's actually so fundamental to everything about. Right.

what a seal does, which is dive. What I'm quite fascinated about is whether or not this is something that convergently evolves and the same selection pressures are across all of those diving animals and to see basically how much diving do you need to do before it becomes really important. Is there going to be an easier way to test this instead of making little tents and having them? Yeah, right. I know it is very time consuming. Of course, you also need...

the animals. Yeah, that's what I'm saying. You're going to do this to a jaguar. You're going to do this to a dugong. Like, how are you going to test it? We're describing phenotype. And I guess the other end of the spectrum is genotype. So what I'm very interested in is trying to look at the gene or gene mutations that underpin that change in sensitivity. And I mean, we have the phenotype described particularly well, I think now in seals, but also in a wonderful little group of animals, the

the mole rats, their phenotype responses, particularly the African mole rat and the Damara mole rat, their ventilatory responses and behavior response are remarkably similar to sales. So I think we have a group of genes central to chemoreception, particularly

Those chemoreceptor sensors in the brain, I mean, the really important ones are something called the retrotrapezoid nucleus and the parafacial nucleus. They just roll off the tongue. These small clusters of neurons that are in contact with the cerebrospinal fluid, really interested in looking at commonality in any of the genes associated with the development or even the transcription of those genes and how that might affect chemosensing and perceptibility of those gases in the animals that we have the phenotype for.

And then that would be quite a nice platform, I think, say, well, we would expect to see that phenotype in a tenrec or in another diving animal. So rather than just taking lots of animals and trying to expose them to mixed gases, is look at the gene a lot like that to sort of pick the kind of animals that we then test the phenotype on. Yeah, very cool. All right, Chris, we got to stop there. I could just keep going forever. Chris, thank you so much. This is a really exciting field to hear about.

Thank you very much. It's been a pleasure to talk to you. And it's always an absolute pleasure to get to talk about seals. So thank you very much for listening. Chris McKnight is a senior research fellow in the Sea Mammal Research Unit at the University of St. Andrews. You can find a link to the paper we discussed at science.org slash podcast.

And that concludes this edition of the Science Podcast. If you have any comments or questions, write to us at sciencepodcast at aaaas.org. To find us on podcast apps, search for Science Magazine or listen on our website, science.org slash podcast. This show was edited by me, Sarah Crespi, and Kevin McLean. We had production help from Megan Tuck at Podigy. Our music is by Jeffrey Cook and Wenkoy Wen. On behalf of Science and its publisher, AAAS, thanks for joining us.

From April 25th to 30th, the American Association for Cancer Research will host the AACR Annual Meeting 2025 in Chicago. This meeting is the critical driver of progress against cancer, the place where scientists, clinicians, and other healthcare professionals, survivors, patients, and advocates gather to share and discuss the latest breakthroughs in cancer research. Both in-person and virtual registration options include access to live sessions,

Q&A, networking, CME and MOC credits, on-demand access to sessions after the meeting, access to the e-poster platform, and more. Learn more about the AACR Annual Meeting 2025 at aacr.org slash aacr2025 and register for the world's most important cancer meeting.