‘Turbocharged’ Mitochondria Power Birds’ Epic Migratory Journeys
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I'm Lauren Good. I'm a senior writer at Wired. I'm Michael Calori, Wired's director of consumer tech and culture. And I'm Zoe Schiffer, director of business and industry. And we're the hosts of Wired's Uncanny Valley. It's a show about the people, power, and influence of Silicon Valley. Every week, we get together to talk about how technology and culture from the Valley are influencing our everyday lives. The internet really was no longer about the early days. It was about minting money.

money. He was swapping out the hoodie for a suit. And it just became like the shorthand for I'm the Silicon Valley hustle coder guy. Or we'll dive deep into the history of some of Silicon Valley's most important institutions and figures. So a lot of people point to parallels between Sam Altman and Steve Jobs. Very good for engagement for Meta for its bottom line, possibly or probably bad for humanity. I don't know if there's any single person that I would trust with this.

Whether you're optimistic or absolutely terrified about what Silicon Valley will do next, this is the podcast for you. We'll be there to bring the analysis and reporting you can only get from Wired. Listen to and follow Wired's Uncanny Valley wherever you get your podcasts. If you want to get from Los Angeles to Seattle, say, you could fly or drive or take a train, but let's imagine that you need to hoof it. There's more than a thousand miles, so it would take a couple months to hike.

At an average jogging pace of, say, five miles per hour, it would be more than 200 hours in total. Now imagine doing that, jogging, but almost never stopping to rest, with barely any food or water. How long do you think before the human body simply couldn't take it anymore?

This is more or less what hundreds of species of birds do, year after year, season after season, on their migratory routes. And we're not just talking about seabirds that are soaring on thermals across the ocean. We mean little songbirds, strenuously flapping their wings, hour after hour, day after day. How do they do it?

Welcome to the Quanta podcast, where we explore the frontiers of fundamental science and math. I'm Samir Patel, editor-in-chief of Quanta magazine. Long-distance migration is one of the most stunning athletic feats of the natural world.

Understanding how birds actually pull it off means getting into some pretty surprising cellular and molecular properties. Here to speak with us today about this is Quanta's biology editor, Hannah Waters. Welcome, Hannah. Hello, Samir. Thanks for having me. We always like to start with the question, what is the big idea? Where are we going with this conversation? The big idea to me is that this is a continent-spanning global phenomenon of animal migration that

that can be explained by traits that are microscopic at the subcellular level. It's really astounding. Tiniest thing to explain the biggest thing. Part of the reason that I think

You're going to be fun to talk to about this subject, Hannah, is that you have a very strong history with birds. That's for sure. Yeah. So the article we're going to be talking about was written by journalist Liz Landau, but I was the editor. I grew up birding. I took a ecology class when I was in high school in which my teacher forced us to memorize by sight local bird species. And I loved it.

And what was your, and I understand this is a term of art in the birding world, what was your spark bird? What was the bird that set you off on your birding course? Yeah, the spark bird was a black-capped chickadee. They nest up in the boreal forest, but they spend their winters in New Jersey where I grew up. And they are just adorable little birds. They're super curious. They'll come up and investigate you. And I guess I always appreciated that about them.

Now, you mentioned these are little itty-bitty birds, the chickadees. You said they start in the boreal forest, which is up in the northern tundra of North America. They end up in New Jersey. So they're going on a long-distance migration. So talk to me a little bit about migration as a behavior, a

among little songbirds like this? Yeah, so migration is this seasonal movement of birds, and lots of animals do this, where they move from one area to another, tracking resources, good weather. Basically, every bird family has some kind of north-south migration. They are breeding in the Arctic in the north, where there's very few predators, there's a lot of food, and they're

And then when it gets too cold for the winter, they fly back down south and they spend their winter in the tropics. So it's this annual cycle where they're going north and then coming back south again twice a year in spring and fall.

And there's obviously a lot of forms of migration in the natural world. There's deal migration, which is aquatic species migrating up in the water column and then migrating back down. There's the famous migration of wildebeests and other large mammals in Africa. All of those, though, like if you've seen the wildebeest, they're kind of ambling along in big herds. And yes, it is challenging, but there's food for them to eat along the way. They can stop whenever they want to.

There's something a little bit different about the migration of birds, and in particular these little songbirds that we're talking about, because physiologically that's not what they're doing. Like they're not ambling north for a while with food under their feet. Talk to me a little bit about what migration is as a physiological feat. So I'll give a few examples. One is the ruby-throated hummingbird, the super tiny bird, one of the animals with the highest metabolisms in the world.

They flap their wings 60 times a second. 60 times a second? 60 times a second. So they'll leave South America and they'll fly for almost 20 hours straight, flapping 60 times a second across the Gulf of Mexico. They don't have big wings. They don't soar. Like, they're flapping the entire way. Yeah, they have just this one way of doing it. And so it takes them almost a full 24 hours of nonstop flapping. When usually these are birds that, during their normal feeding, they have to

drink nectar from so many flowers every day that if they even miss a few, they don't have enough energy. So obviously something different is happening during the migration season. Another example is the bar-tailed godwit, which is a shorebird. It has the longest nonstop flight that's ever been tracked. One that was tagged flew for 8,000 miles between Alaska and New Zealand, and it did this in 11 days without stopping for food or rest. Wow.

How do you fly for 10 days straight, no rest, no food? I know we're going to talk a little bit about some of the molecular and cellular things that might be going on. But prior to this new research, like what do we know physiologically about how birds manage this like crazy athletic feat?

There clearly is a physiological shift that occurs. And it seems like when the birds can sense that the days are getting longer, there's more light every day, there's hormonal changes. So they've actually measured this, that there's a shift in their hormones that then triggers all of these changes. So one of them is, I mean, they eat a lot. So they...

eat so much fat, they eat tons of berries. And so a hummingbird will double its body weight before it migrates. Well, which is like from half an ounce to like an ounce. Like hummingbird body weight is not exactly a lot. But for a hummingbird, it is. I mean, you have to carry that weight. But yeah, a lot of birds will double their body weight.

Another example is their hearts in some species will enlarge so that they can pump more blood through their whole body. Those bar-tailed godwits I mentioned, they will absorb the tissue in other organs that they don't need. So they'll consume a quarter of their liver, kidneys, and digestive tract and just take that material and use it elsewhere. Wow. So the light changes. It's a seasonal response that leads through millions of years of evolution.

to a hormonal change that leads to all these physiological things that enable their migrations to happen. But even if you're doubling your weight, how does that lead you to be able to make that giant migration at a fundamental level?

Well, it comes down to the organelle called the mitochondria. Okay. So let's talk a little bit about mitochondria. What are they? In just about every cell in your body and in any multicellular animal are mitochondria, which is an organelle. It's called the powerhouse of the cell, and it processes energy for the cell. So it takes in oxygen and glucose or food,

and breaks it down and creates molecular energy, which then can get passed around and used for all different kinds of reactions in cells. And what's interesting about the mitochondria, and this goes back to a theory in the 1960s by Lynn Margulis, is it was likely originally a free-living bacteria.

So a mitochondria was its own cell that was living independently and had this special talent for processing energy. Yeah. And then through a process called endosymbiosis, an ancient cell that was our ancestor enveloped and formed a relationship with this cell that became our cellular mitochondria. Some people speculate that the mitochondria is the reason you can have multicellular creatures at all. Right.

It sounds like in recent decades, our understanding of mitochondria has gotten way more complex. Yeah, they can divide and fuse just like another cell. You have mitochondria in some tissues that can specialize for different tasks. That's another thing that's really come out is that mitochondria aren't just creating this ATP, this molecular energy. They're also doing all kinds of other chemical reactions in the cell.

And what's fascinating is they're also social. Whoa, stop. Yeah, there's evidence that mitochondria are actually talking to each other, not only within your cells, but also across your tissues.

So you can imagine, like, you know, you take in some molecule from the environment, the mitochondria processes it, and I want to tell the other mitochondria about it. And that's because it has this origin as its own cell. Okay, so we know that one of the main roles of mitochondria is energy. But how do we find out what role mitochondria play in making it possible for birds to do these crazy physiological things?

It's a question that a couple of labs went out to answer over the last few years and published three different major papers that have all tried to compare the mitochondria and the cells of birds that migrate versus those that do not. Basically, ask the question, are there differences in the mitochondria between these two groups of birds? But you can't just take any random bird that migrates or doesn't. You either have to find birds that within the population are migrating or not, or you have to create them yourself. What do you mean create them?

So that's what one of these groups did. They captured yellow-rumped warblers, which are a little songbird in the field, and brought them into the lab.

And then, because we know that light triggers these physiological changes, they expose these warblers to different amounts of light. So like a longer day length or a shorter day length. And so they actually generated two populations. A migratory population. Migratory, quote unquote, they're not migrating. They're expressing the traits of birds that are ready to migrate. Versus a different population, which is non-migratory. And these don't express those traits. They are the more resident. Right.

So scientists in the lab have a group of birds that are not prepped for migration and a group of birds that are. So what are they looking at next? So they want to look at their mitochondria. So they do this by measuring the ATP that the mitochondria are producing. And as a proxy, how much oxygen are the mitochondria processing?

And so, yeah, they found that those birds that were in that migration group, their cells had more mitochondria and those mitochondria had a greater capacity to make energy. So they were producing more energy for the same amount of food is one way to think about it.

I would assume that turning up your mitochondria by having more of them in your cells or by having them produce more energy comes at a cost physiologically, right? Otherwise, we would have them all the time and we would be giant balls of energy.

Yeah, the problem is that when the mitochondria does this processing, they create what are called reactive oxygen species. These are molecules that can damage DNA. So then the cell has to have all of these backup mechanisms by which it can clean out these reactive oxygen species. It can bundle up damaged molecules. So then you end up spending more of your energy actually cleaning up your own mess. So there is kind of like an optimal, efficient amount of energy that we have evolved for.

Now, birds need time to recover at the end of these migrations, right? Is there like a migratory hangover? Yes, they can be very exhausted when they land. Sometimes birders will witness what we call a fallout. They kind of all fall out of the sky in a single spot. And you'll see like dozens of bird species flying together, hundreds or thousands of them, all landing in the same spot because they just need to take a break, eat food. There was a study that found they specifically look for berries that have antioxidants.

to help them deal with these reactive oxygen species and this damage to their mitochondria. Yeah, so absolutely. They're exhausted, they collapse, and then they need a minute to recover. Right. And then presumably their mitochondria go back to normal? Yeah.

You mentioned there were several papers that came out that were looking at mitochondria in migratory birds. What are some of the other work finding out? Yeah, so the other work was out of another lab. They took a slightly different approach. They collected birds in the fields that were migrating and not. And so they drove what they call the mitomobile machine.

So it's a mobile lab in an RV. Dedicated to mitochondria. Yeah, it literally says mitomobile on the side. So it has, you know, lab benches and it has all of the machinery that you need to, on the spot, do this oxygen analysis and to measure the metabolism of these mitochondria. What they did is they looked at a different species of bird called the white-crowned sparrow. You can find it all across the United States, different times of year. And there are different subspecies of this sparrow. So some of them migrate.

And some of them don't. Ah, natural laboratory. Exactly. We love birds. So they went and captured some birds that were on their migration route at a known stopping place where they're known to rest. And then they captured another group of birds that are known to be resident. And then they made the similar comparison that the first group did. And so they independently on their own kind of found the same stuff. The birds that were migrating generated more energy with their mitochondria and they had more mitochondria.

Let's take this a level deeper. What is actually happening to the mitochondria? How are they changing? What are they doing to produce more energy for the birds?

We don't have a completely sure answer to this, but one of the scientists in that second lab, Paolo Moschitta, he did another set of molecular biology experiments. So using the same birds from the wild collected birds, but he then did a molecular biology study to look at protein markers. Okay, what are those? So they're basically just protein indicators that have previously been associated with changes in a mitochondria's shape.

Okay. When a mitochondria changes its shape, there's certain processes that goes through. And previous studies had found that there are certain proteins that we don't know what role they play in the process, but they're involved. So then you can use those proteins as a tracker and basically say, are the mitochondria changing? And he did find them just in the flight muscles, but not in the leg muscles of these migratory birds.

That's interesting because that means that the birds' physiological changes are targeted specifically to the muscles that they need to make the migration flights. Yeah, absolutely.

Okay, so we have to speculate. Birds are warm-blooded, eukaryotic animal species, and so are we. So we have cells full of mitochondria. We have a lot of physiological changes that happen when you exercise. What does this mean for us understanding how our own bodies work?

Yeah, I think there's kind of a couple ways to look at this. One is people who exercise a lot or lift weights, they do increase their number of mitochondria in their cells. So there is a possibility there. The difference, though, is birds just turn it on. Yes. Just the light hits and suddenly they have their mitochondria, where in humans it takes months of training to see any kind of effect like this.

So Paolo Moschitta, one of the researchers, speculated, is there a way that we could potentially make a drug to enable this in people? Another way to think about this is birds as a model organism for studying exercise. I was talking to a friend who's a weightlifter, and he was really interested in this. Like, oh, birds get more mitochondria. How do I turn up my mitochondria so that I can lift more? Exactly. And what can we learn about our own musculature and our own exercise physiology? Yeah.

from these little birds that really are quite athletic a couple times a year. Yeah. It's fun to think about. So, Hannah, we'd like to end the podcast with a recommendation. What's exciting your imagination this week?

I recently read a novel that I wanted to recommend to our listeners. It's called Orbital by Samantha Harvey. It's a short little novel and it won the Booker Prize last year. And it takes place on the International Space Station and follows the internal monologues and reflections of six astronauts that are living up there.

And what I like about it is it really alternates between the mundanity of their existence, living in a can, trying to keep themselves exercised and fed and doing their little scientific experiments. And then the profundity as they reflect on being in space, looking back at Earth and having all these realizations. I love it. Thanks, Hannah.

Also on Quanta this week, you can read a physics story that explores the idea that gravity actually comes from entropy and another biology story about how you can model an entire complex ecosystem in a lab. So you can check out these stories along with Liz Landau's story about birds. It's called Turbocharged Mitochondria Powered Birds Epic Migratory Journeys.

We're going to leave you today with the interweaving songscapes of two migratory birds, the hermit thrush and the white-throated sparrow. They were recorded by Lang Elliott for his website, musicofnature.com. The Quanta Podcast is a podcast from Quanta Magazine, an editorially independent publication supported by the Simons Foundation. I'm Quanta's Editor-in-Chief, Samir Patel.

Funding decisions by the Simons Foundation have no influence on the selection of topics, guests, or other editorial decisions in this podcast or in Quanta Magazine. The Quanta Podcast is produced in partnership with PRX Productions. The production team is Ali Budner, Deborah J. Balthazar, Genevieve Sponsler, and Tommy Bazarian. The executive producer of PRX Productions is Jocelyn Gonzalez.

From Quanta Magazine, Simon France and myself provide editorial guidance with support from Matt Karlstrom, Samuel Velasco, Simone Barr, and Michael Kenyongolo. Our theme music is from APM Music. If you have any questions or comments for us, please email us at quanta at simonsfoundation.org. Thanks for listening. From PR.