The genetic secret helping bats survive a deadly epidemic

We’re easing you into Halloween season with an episode about bats. There’s a silent serial killer decimating little brown bats as they hibernate. White nose syndrome has driven populations across the U. S. to almost the brink of extinction over the last decade. But recently, conservation biologist Giorgia Auteri https://sites.google.com/view/giorgia-g-auteri/home?pli=1&authuser=0 and her team noticed several genetic mutations in the survivors. These mutations could explain how natural selection has shifted the existing population – and inform conservation efforts in the future. Interested in more animal science? Email us your question at [email protected] mailto:[email protected]. Support public media with NPR+ and enjoy perks for over 25 podcasts like this one. This show’s perks include sponsor-free listening. Learn more at plus.npr.org http://plus.npr.org. See pcm.adswizz.com https://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 https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:17Speaker 01

  You're listening to Short Wave from NPR.

• 0:22Speaker 01

  Hey, Short Wavers. Okay, let's talk about bats. Part of me thinks they're cute. I mean, I love Batman, and part of me thinks they're scary. So at baseline, I'm conflicted about how to feel about them. That's how I entered a conversation with Short Wave producer Hannah Chin not long ago, when they told me bats in the US are in danger. And of course, when I learned that, I immediately thought WWBD, like, what would Batman do?

• 0:52Speaker 02

  What would Batman do? I think that he'd investigate.

• 0:55Speaker 01

  Yeah, I mean, he's the world's greatest detective. That's what he's known for.

• 0:59Speaker 02

  Well, today, Gina, you and I are the bat detectives.

• 1:02Speaker 01

  Okay.

• 1:02Speaker 02

  And I'm going to start our detective journey by telling you about the bat walk I went on here in New York City. It started like pretty much any other nature walk. We all convene in the parking lot. Everyone seemed really excited. I met quite a few people there. Parker, Julie, Bella, Andy. I'm wearing this shirt that my best friend got me with like all these different kinds of bats on it.

• 1:23Speaker 03

  It says little brown bat with a drawing of a cute little bat.

• 1:29Speaker 02

  It was bats galore.

• 1:32Speaker 03

  I noticed that you have a bat tattoo. I do.

• 1:35Speaker 03

  I just got it. It's a little stick and poke.

• 1:37Speaker 02

  Everyone was so thrilled about even the possibility of seeing a bat.

• 1:42Speaker 03

  I do like bats. I've never done a walk like this.

• 1:45Speaker 04

  We were like, are we going to be the only ones here? And then everyone showed up. There's a lot of people.

• 1:49Speaker 01

  It seems really popular. And honestly, like, I don't think I've seen a bat that up close. I've seen them in the sky, pretty far away, knowing it's a bat.

• 1:58Speaker 02

  Yeah, there were maybe 20 of us wandering around the Ridgewood Reservoir. And our guide, Nick Camparato, gave us a little bit of bat background.

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  So here in New York City, the most common bat I see, and the most common bat I get in my research, is the eastern red bat. Big brown bat I also see quite a bit. Hori bat I get sometimes, not as much as I'd like to.

• 2:17Speaker 02

  Nick's a bat biologist and a PhD student at Rutgers University, and they lead these summer bat walks. But Gina, this is where the detective part comes in.

• 2:25Speaker 01

  Right, right. Because along the way of making this episode, we learned one of the main things endangering bats around the country right now is a deadly illness called white nose syndrome.

• 2:34Speaker 03

  White nose syndrome is a disease affecting bats. It's caused by an introduced fungal pathogen that probably was human transported from Eurasia.

• 2:43Speaker 02

  This is Georgia Oteri. She's a conservation wildlife biologist, and she works for Bat Conservation International. She told us that the type of fungus that causes the disease really thrives in cool, humid environments.

• 2:55Speaker 01

  Like the bat cave, or I'm guessing real life caves as well.

• 2:59Speaker 02

  Exactly, which a lot of bats hibernate in. And this fungus, it can grow on the cave walls or the ground, even on the bats themselves.

• 3:08Speaker 03

  Because when they're hibernating, their body becomes cool enough that the fungus can grow on them. And the fungus actually starts secreting things that like break down their tissue of their body and starts kind of eating them alive while they're trying to conserve energy and hibernate.

• 3:23Speaker 02

  It's just really brutal. Nick told me for a while, every time they've gone to a bat conference, there were scientists in tears, just mourning the loss of all of these bats to this unstoppable virus. But Georgia and her colleagues realized that some bats are surviving.

• 3:40Speaker 01

  So we're talking to her for this episode. Today on the show, the deadly fungus that's decimating bat populations in the US, and how some bats are able to survive it. You're listening to Short Wave, the science podcast from NPR.

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• 5:29Speaker 01

  Okay, Georgia, so even though we might not see them, bats are everywhere, you know, in the US. They're in caves, they're in trees, you know, like inside the hollows. And they kind of span the whole country. But there are actually fewer and fewer bats out there because of this white nose syndrome, right?

• 5:45Speaker 03

  Yeah, absolutely. Especially out in the East and Midwest.

• 5:50Speaker 01

  So do researchers know how it got there?

• 5:52Speaker 03

  We don't really know for sure, but probably like someone was just in a cave or something over there. And then they came over and spores got into, you know, suitable habitat here, which was in underground caves and mines. And then this fungus started proliferating.

• 6:09Speaker 01

  Right. So like, it grows on the bats, it infects them during hibernation while they're sleeping, right?

• 6:16Speaker 03

  Yeah, while they're trying to sleep, they basically end up waking up from hibernation when they should be sleeping and conserving energy. That's how this fungus ends up killing them.

• 6:25Speaker 01

  What exactly do bats die of when they're infected with white nose syndrome? Like, is it starvation? Or is it because they're waking up more often? Or is it just more complex than that?

• 6:35Speaker 03

  Yeah, I usually say that they're dying of secondary physiological complications associated with waking up too much from hibernation. Because it's a little bit of like, sometimes that could lead to death from starvation. Sometimes it might lead to death from dehydration, just like waking up. But usually, it seems to be mostly like a starvation thing. It can also kind of be like an autoimmune response. Like, sometimes their immune system goes too crazy.

• 7:02Speaker 01

  Because they're trying to fight off this mold.

• 7:05Speaker 03

  Yeah, and it's kind of like a syndrome that was observed in people with like, fighting off HIV and AIDS, where they have kind of the same thing. They have an autoimmune, like a really harmful autoimmune flare-up response. So it seems there's evidence that some of them are experiencing that as well.

• 7:21Speaker 01

  That's terrifying. And so like, which species of bat are these affecting the most? These cave bats, I'm guessing?

• 7:27Speaker 03

  It mostly affects cave bats. And some of these cave hibernating bats, it doesn't affect as strongly, like maybe because they're a little bit bigger, or they just have a different hibernation pattern. But right now, there's 12 species that are affected by this disease, 12 species of bats. One of them, the little brown bat, was previously the most abundant species of bat in the eastern US. And so its numbers have just tanked. It's had over 90% declines, often over 95% declines, depending on the area.

• 8:03Speaker 01

  Yeah. But I'm glad you brought that up, because I want to focus specifically on the little brown bat for the rest of this episode. And there's good news, right? Because some little brown bats survived. Why do we think that is? Like, can you tell me a little bit more about how that happened?

• 8:20Speaker 03

  Yeah, totally. So when white nose syndrome swept through, it killed most of the little brown bats. But a subset of them survived. And those survivors, it seems like, oftentimes were genetically better disposed to survive, like frequent waking up from hibernation because of the fungus. So maybe they had things, like they were genetically predisposed to have higher fat reserves going into hibernation, or maybe they were genetically predisposed to wake up less frequently. We don't, we're still fully understanding how that happened. But basically, we had a big population with lots of genetic diversity. We killed off a bunch of them selectively. And now the remaining bats tend to have different versions of some genes compared to the ones that died.

• 9:05Speaker 01

  Right. So we have this genetic variation in this very diverse population of little brown bats. Why are scientists interested in studying these surviving bats and their genes?

• 9:15Speaker 03

  Yeah, I mean, I think there's two reasons scientists are interested in studying these survivors. One is that from a theoretical standpoint, it's really cool to see evolution in action. It helps inform our basic understanding of science. And it's like, oh, things are, actually get pretty complicated and tangled pretty quickly. And then, well, the second reason, though, is that it's really helpful for informing conservation efforts, sort of helping us tailor the nature of our conservation to the ways in which the species themselves are adapting to white nose syndrome.

• 9:49Speaker 01

  And this is something you're researching, right? So like, what has your research found with these bat survivors?

• 9:54Speaker 03

  Yeah, so the work that I'm working on now, gone in a couple different directions. So one was to try to look at the physical characteristics of the survivors and look at how those vary. And one of the things we did find is that like, bats, when they're getting ready to go into hibernation, if they have a certain adaptive gene, they tend to have a higher body mass index. This, of course, makes a lot of sense, right?

• 10:16Speaker 01

  Yeah, they have more reserves before they go to sleep.

• 10:19Speaker 03

  Yes, exactly.

• 10:20Speaker 01

  Okay.

• 10:20Speaker 03

  And so when you're hibernating, you're saving energy. And every time you wake up from hibernation, it's extremely energetically costly. Bats are really only meant to wake up a few times during the winter in order to have enough fat to make it through. So it could be that waking up less often, like just staying asleep and letting the fungus eat away at you, is actually a better way to get through the winter than waking up. It could also be that maybe some bats are like, good at waking up but falling asleep really quickly again. That way, each time they wake up, it's less energetically costly.

• 10:57Speaker 01

  It makes me think of like the aughts and like, you know, turning on and off your computer took up so much energy that you like, keep it on, you know? So it's like the waking up and falling asleep takes so much energy.

• 11:10Speaker 03

  I should say, this is getting to kind of like another point, which is that unfortunately, it's not like a one-to-one relationship with genes and their functions. Like oftentimes, we don't really know.

• 11:19Speaker 01

  Right.

• 11:20Speaker 03

  And also, even more critically, a lot of times, one gene actually affects multiple different traits of a species. And so it makes it really tricky. Like if you're a bat, you can't just optimize yourself for White-Nose Syndrome without changing something else. A lot of times, there's trade-offs. I guess like the second prong right now of my current research is looking at whether bats are evolving to White-Nose Syndrome in part via reproductive trade-offs, trade-offs in reproduction.

• 11:53Speaker 01

  Oh, OK, interesting. So what do you mean by trade-offs of reproduction?

• 11:57Speaker 03

  I would think about it like this. Like, let's say you are a female little brown bat. Little brown bats actually are pregnant. They become pregnant in spring. And then they migrate out of their caves while pregnant to their summer tree or wherever that they're gonna have.

• 12:15Speaker 01

  Their beach house.

• 12:16Speaker 03

  Yeah, to their beach house. Let's say then that something goes wrong with the pregnancy, or maybe, oh, just kidding, I'm not actually pregnant. Guess what? Instead of spending the spring and summer raising a baby and nursing that baby and taking care of it, she potentially has a lot more energy to spend just on herself and maybe recovering from White-Nose Syndrome.

• 12:37Speaker 01

  She's having me time.

• 12:38Speaker 03

  Yeah, fall comes, and she's much healthier possibly compared to the females. She has higher BMI, higher fat reserves. She's ready for hibernation. She's potentially much more likely to survive compared to those other female little brown bats. These bats have a really slow life history. So that means that they live a long time and they don't produce babies very often. But yeah, little brown bats, they typically just have one pup a year. And they'll live for up to 34 years in the wild is the record right now. And like, for context, like, White-Nose Syndrome was discovered in 2006.

• 13:17Speaker 03

  So like, at ground zero, where it was discovered, it won't be until like, 2040, that the last little brown bat would hypothetically die that was born before White-Nose Syndrome. So we potentially have a lot of well-adapted adults flying around that aren't necessarily reproducing young at the rate we would like, because it takes a lot of energy to survive the disease, and it takes a lot of energy to raise a baby.

• 13:43Speaker 01

  Yeah, there's a trade-off, right? You have survival at the cost of potentially not reproducing.

• 13:49Speaker 03

  Mm-hmm. Yeah, exactly. To kind of draw it full circle, like, the gene that I found that is most associated with higher BMI, higher pre-hibernation BMI in bats with White-Nose Syndrome, that same gene in humans is associated with earlier onset of menopause and pregnancy disorders.

• 14:13Speaker 01

  Could we see this continuing decline, or even a faster decline, of the little brown bat population if the survivors are having babies at a slower rate?

• 14:23Speaker 03

  Yeah, I think we could see a continued decline just at a slower rate. We could see, you know, stabilization just at these newer, lower levels. Or we could see increasing populations, depending on, you know, what genes are under selection in that population. And indeed, we actually see all three of those things, depending on where we look in the US. So I think looking at the genetics really helps us understand what's going on in the broader picture.

• 14:53Speaker 01

  Georgia, thank you so much for coming today and talking to us about bats.

• 14:57Speaker 03

  Yes, definitely. Thank you so much for having me.

• 15:03Speaker 01

  If you liked this episode, share it with a friend. Maybe a friend that goes to cons and takes pictures with Batman. I did that. Or a friend that loves all those critters that some people find really scary.

• 15:16Speaker 01

  This episode was produced by Hannah Chin. It was edited by showrunner Rebecca Ramirez and fact-checked by Tyler Jones. The audio engineer was An Li Huang. I'm Regina Barber. Thank you for listening to Short Wave from NPR. See you next time.

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