Short Wave - Snow Flies Pay An Arm And A Leg For Love

Episode Date: January 5, 2024

The winter is usually when insects die or go into a state of paused development, but for tiny specks on the white snow called snow flies, it's time to run around, find a lover and make baby snow flies. Neuroscientist John Tuthill has been studying these creatures since he first came across them in 2016. He's found that not only can they survive in the cold, but if one of their limbs starts to freeze, they can self-amputate and pop it right off. That buys the snow fly time to find a mate and make sweet, sweet snow fly love.Interested in other winter biology? Email us at [e-mail] — we'd love to hear from you!See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, shortwavers, Sydney Lepkin filling in the host chair today. So around this time of year, about 5,000 feet above sea level in the mountains, you might see fresh snow. In a place just like this, the enchantments in the Cascade Mountains of Washington State, about seven years ago, neuroscientist John Tuttle went hiking. He says it was beautiful but windy, avalanche territory. like one of the most inhospitable places you could imagine. And I just remember seeing an insect on the snow and kind of being like, wow, that's crazy.

Like how is it possible that this insect is out here doing this? John says these insects were moving uphill, basically running. And even though they're tiny, they stood out against the rest of the mountain. So you can kind of spot them out of the corner of your eye. It's this like big, open, white expanse. There's nothing on it at all except for this one little dot in the distance. that's kind of slowly moving. These little dots in the snow are called snowflies,

and they seemed unusual to John because these conditions are a death sentence for lots of other insects. Once it gets so cold that they can no longer move, then they're screwed. Like they're essentially in this catatonic state, and they can't overcome that. And that happens quite frequently

as the insects get blown up into a place where it's too cold for them ever to move again. Even the other insects that don't die still go into a state of pause development, which John knew as someone who spends a lot of time studying fruit flies for his job. He's an associate professor of physiology and biofysics at the University of Washington. If you were to take a violet fruit flies out and just kind of expose it to the snowy temperatures where snowflies live, their internal body temperature would gradually decrease until it was basically the same temperature as the ambient air. At that point, they go into this state

called chill coma, where to kind of preserve the function of their bodies, they shut everything down. They kind of like turn off the engine in order to preserve their physiological functions for hopefully some later date when it will warm up again. But snowflies, they're somehow thriving in these super inhospitable conditions in the mountains. On that trip, I saw more and more of them and realized like this is a common thing that is happening, these animals are out here wandering around over the snow. It's not like just some random insect that was blown up here by the wind. Like, these animals actually live here.

So today on the show, the insects finding life and love in the freezing cold against all odds and the funky adaptation they have to keep them moving. You're listening to Shortwave from NPR. Okay. So, John, first I want to talk about like freezing itself. I think a lot of people just sort of imagine it as like, okay, well, anything under 32 degrees Fahrenheit, zero degrees Celsius, that's freezing. But freezing is actually a whole process that happens in the body. It's not just a number, right? Right. Let's say you have a cup of water and you cool it

down from like room temperature to freezing. It won't just suddenly instantly crystallize at zero degrees into a block of frozen ice. Like there's a process that happens where ice crystals forms through this process called nucleation. So ice actually generally forms around like a little particle that's in the water. And so there's a common chemistry demonstration, which is to cool down distilled water colder and colder and colder until it's well below zero degrees Celsius. And then you add something like a grain of salt to the cup of water and then the whole thing freezes instantly. And so that's what happens in animal bodies as well, is that as an animal's internal body temperature gets colder and colder and colder, at some point usually well below zero, there'll be an

ice nucleation event where an ice crystal forms and then ice kind of spreads throughout the animal body and leads to, in the case of a snowfly, for example, like a kind of traveling wave of ice often through its legs. Oh, wow. Okay. So you did an experiment looking at what happens when snowflies get close to freezing. How do you run an experiment like that? Like, what does it look like when you're doing that? The way we do it is that we have a little chamber. It's just a cold plate. And we just gradually lower the temperature of the cold plate down. And we have a very fancy thermal camera that we got, there was very high magnification and allowed us to essentially see what the body temperature of the snowfly was as we changed the temperature of the cold plate

that we're using to measure the snowfly's behavior. And the reason we had to do this is that people generally measure an animal's internal temperature by sticking a little probe into the animal, like a tiny little thermometer. But we couldn't do that because the animals are running around so much that they would essentially remove the pro from themselves. It's important to know at this point also that the snowflies don't have wings. It's generally true

that insects that live in cold temperatures through evolution lose their wings because sustaining flight is extremely energetically expensive and hard to do when it's cold. So these are wingless flies. And so they're in this chamber just walking around. And so we can lower the temperature

of the cold plate to kind of mimic the conditions that they experience in cold natural environments. Can we still call them flies if they can't fly? Yes, for sure. And how do they get around and eat in stuff with no wings? They just run around. They run?

Yeah. As a runner, I like to call it running because I can just tell the flies are really exerting themselves. They're moving at just a faster clip than like your average walking fruit fly. Okay. So back to that experiment. What did you find? The first thing we saw was that the snow flies temperature, essentially tracks that of its environment.

So, like, one hypothesis we have is that they're like us, they thermoregulate, they actively increase their body temperature so that they're warmer than their environment. And that would allow them to keep moving. But that's not what we found. They're slightly warmer than the cold plate, but that's just because they're elevated above it slightly. For the most part, their internal body temperature is basically the temperature of the environment. Okay.

So what happens when it freezes? It's still walking around. basically up until the point that we observe, which is when they freeze. But then at some point, what we observed in the thermal imaging is that there's an ice nucleation event that happens within the snowfly. And the way that this looks on the thermal camera is the tip of the fly's leg suddenly increases in temperature. And that indicates that there's been the formation of ice crystals in the snowfly's leg.

Because when ice forms, it's actually an exothermic reaction. So heat is released. And then you see this wave of ice traveling up the snowfly's leg. And over about the course of a second, it moves from the snowfly's toes to its tibia, to its femur, and then eventually reaches its body. And at that point, then ice spread throughout this whole snowfly's body. And that's the end for the snowfly. They free solid and they die. So it happens no matter what?

What makes the snowfly special? I thought this wasn't going to happen to them. The thing that makes the snowfly special is that they're able to keep running around all the way down to that temperature where they freeze solid. Their muscles and their neurons and all the physiological processes in their bodies continue working at these internal temperatures where other animals would not be able to operate. And don't they do one extra special thing to keep them alive a little longer? Sometimes the snowfly will actively detect that its legs are free.

freezing and then amputate their leg very quickly before the wave of ice reaches their body. So what that does is it basically buys them more time to try and find a place in the environment where it's not as cold. Is there something that they might be doing with that time that increases their survival, their overall species survival, anything like that? The way I think about it is that they're outliving in these super inhospitable conditions. Their goal as an adult snowfly is to find another flying mate. And so basically any additional time that they can buy gives them a little bit better chance of finding a mate and reproducing.

But their relatives, the crane flies, amputate their legs for different reasons. And those reasons are mainly related to predation. So if you have one of these big, goofy crane flies that are flying around in your house and you try and grab it and you happen to grab one of the legs, the leg will pop off. So that's a pretty similar mechanism of self-amputations. And it's pretty clear in that case that the reason that the crane flies do that is that they are trying to avoid being caught by predator. So the way we think about it, I mean, it's very hard to prove this. It's an evolutionary argument is that at some point crane flies that already were able to self-amipitate their limbs to avoid predators, gradually figured out ways through evolution to live in very cold environments.

And then through some evolutionary switch, they took the capacity to self-amipatting. their legs to avoid predators and applied it to avoiding the predator of ice formation. So, okay, we know that they amputate their legs, but how do you think this actually happens? Like, what's the mechanism for this happening? Yeah, that's a great question. We don't totally know yet, but our theory is that the snowfly's leg has a receptor at the tip of the leg. It's actually a thermal receptor. And we haven't shown this yet.

This is just our hypothesis based on a bunch of evidence we've collected. But we think that they're detecting an increase in temperature when ice forms. And what we know is that there's a specialized muscle at the joint that amputates. And so we think this thermoreceptor in the leg senses that there's a rapid increase in temperature, which is caused by ice formation. And that that receptor then triggers activation of the muscle that is used. use to amputate the leg. And there's still a small chance that they'll meet the love of their life and end up being able to procreate. Wow. And then I have to ask because, you know, we want these

sometimes snowfly amputees to find love. And you said that you're putting them in some of these containers together. Have any of them found love and laid eggs in the container? If you put a male and a female in together, they will immediately start mating. On the Snowfly Project Instagram page, Some of the fan favorites are snowflies making love in the tube of desire. Oh, man, that's so sweet. So wholesome. What does this research sort of tell us about cold adaptation more broadly? Like, what does this tell us about the world in our everyday lives that we live in? There is still a huge mystery as to how it is that they've adapted physiologically so that their neurons and their muscles and their guts and all of the, systems that they have, that we have, how those work at these very cold temperatures. And so we're now

at the point where we can say definitively, like, these animals are able to live at these internal body temperatures way below other animals. And so how it is that they're accomplishing that, do they have some special sauce that they use to kind of make their muscles and their neurons work at these very cold temperatures? That's still a huge open question that we're interested in pursuing. And are there lessons in, you know, life and love? For me, snowflies are just kind of a paragon of, of like, fortitude and bravery. Like, they have figured out how to live in an environment where there's almost no other insect. And the advantage of that is that they have a place where they can make free love on the snow with each other without interruption from predators in, like, incredibly beautiful.

conditions often. I love that. I really love that. John, thank you so much for joining us today. This was awesome. All right. Thanks for having me. This episode was produced by Rachel Carlson, edited by our showrunner, Rebecca Ramirez,

and fact-checked by Burley McCoy. Josh Newell was the audio engineer. Betz Annamet is our senior director, and Colin Campbell is our senior vice president of programming. I'm Sidney Lubkin. Thanks for listening to Shortwave from NPR. Bye.