When, and where, did bats first take to the sky?

An analysis of bat genomes and fossil records has shown that the flying mammals first took wing in Europe some 60-65 million years ago.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:02Flora Lichtman?

  Hey, it's Flora and you're listening to Science Friday. Tomorrow is Halloween, meaning you only have a few hours to get your costumes together. But consider the bat. Researchers now believe that iconic Halloween creature has been perfecting its form for the last 60 to 65 million years. Dr. Emma Teeling is part of a global team working to answer the question of where and how the first bats evolved. Hey, Emma.

• 0:32Speaker 01

  Hi, how are you doing, Flora?

• 0:34Flora Lichtman?

  Happy Halloween.

• 0:35Speaker 01

  You too.

• 0:37Flora Lichtman?

  So, your group recently published this deep dive into where bats first took flight. What did you find?

• 0:43Speaker 01

  So, the Bat1K Sequencing Consortium, so a consortium that we're dedicated to sequence the genome of every living bat species. We sequenced 103 bat genomes to reference quality assembly. And we coupled that with 65 fossil bats, and we were able to integrate the genomic and the fossil data together. We made evolutionary trees so we could understand the evolutionary path that bats have evolved into. We also worked out where did they evolve? Where did bats originate? So, they evolved about 65 million years ago in Europe, allowing us to refute different

• 1:27Speaker 01

  hypotheses they evolved in North America, Africa, or Asia. We also worked out how did they move around during those timeframes? And we reconstructed the ancestral genome of the first flying mammal, which was a bat.

• 1:44Flora Lichtman?

  Were these sort of seismic discoveries in your world? Like, were people pushing back or surprised?

• 1:49Speaker 01

  Oh, yes. With the evolutionary tree still, you know, this was, I've been working on this since 1997. And we found some really crazy things about bats that were some of the most advanced echolocators grouping with the non-echolocating bats. And thankfully enough, we still supported that with our new study. We also found that the bat genome, one of the reasons why it was so difficult to reconstruct the evolutionary history and path of bats was that the genome is highly mosaic. So, bits of the genome will give you one evolutionary history, and then you'll sequence another part and it'll give you something different. And this is because they seemed to be able to hybridize quite a lot. So, we rewrote the evolutionary history.

• 2:34Speaker 01

  And papers that I published, I said were wrong, right?

• 2:38Flora Lichtman?

  Wow, you overturned your own work.

• 2:41Speaker 01

  Well, yes, and much easier for us, me, than somebody else, as we did do that. Now, there's about 1,500 species of bats that we now recognize in the globe. One in five every living mammal is a bat.

• 2:54Flora Lichtman?

  That's a lot, just to chime in there. One in five.

• 2:58Speaker 01

  One in five are bats, actually. And they're really, really diverse, and they're found all around the globe. They're divided up into kind of 21 different family groups. But what we wanted to do was, we wanted to understand, when did bats evolve in relation to all other mammals? Where did they evolve in relation to all other mammals? And we also wanted to then have these genomes and this evolutionary path network that we could use, so a phylogenetic tree, that would be able to hang on the other unique traits that bats have, to understand what is the DNA? What are the genomic bases of their unique traits?

• 3:40Flora Lichtman?

  I'm all in. Let's take these one by one.

• 3:42Speaker 01

  Yes.

• 3:43Flora Lichtman?

  Let's start with the when.

• 3:44Speaker 01

  Yes.

• 3:45Flora Lichtman?

  You found 60 to 65 million years ago. What's going on with other mammals at the time? So, to set the scene.

• 3:51Speaker 01

  So, this is when our dinosaurs went extinct. This is when the meteorite hit the Earth. There was night potentially for over two years. And bats seemed to respond to this. So, the ancestral bat, like, the modern bats that we see today, we have argued that they originated about 65 million years ago. But they were evolving for about 20 million years from other different mammalian ancestors, but started to-

• 4:19Flora Lichtman?

  Oh, like what? Like, what did they, where did they come? What animals did they come from?

• 4:22Speaker 01

  That's a brilliant question. This is still one of the open-ended questions in biology. So, bats fall in a group called Ageria thuria. Now, in this group, what you have is the first branch that branches out of this group that originated about 80 million years ago are true shrews, so insectivores. Next, you have bats. Then you have this big group which contain the carnivores. So, you're lions, you're tigers and bears, horses, whales, deer, and animals like that that group together. So, bats form in this group. They're not closely related to mice, as people used to think before, but these are the group that the bats are closely related to. So, what we did that was different in this study, and this was led by Liliana Davalos

• 5:05Speaker 01

  and her team, what we wanted to do was, we said, all right, when you go, so the way you make an evolutionary tree, a phylogenetic tree, using molecules, using DNA, is you will line up all of the genomes, and you look through the regions of the genomes, and you see, well, are they the same or are they different in different species? And then you use this evolutionary inference to say, well, which species are most closely related to each other? And typically, it's because their DNA reads the same in those regions. But what we also wanted to do, we wanted to be able to use this wealth of bat fossil record. Now, a bat fossil record is a very unusual fossil record, because about 50 to 55 million

• 5:46Speaker 01

  years ago, and million years of age, you find these beautiful, exquisite, nearly fully-formed fossils, so called Lagostatton fossils. And which means that researchers could see that these fossil bats had wings, because they had very, very long, long fingers. When you look at their skull, you could look at their inner ear, and you could see that they were highly coiled, their cochlea were highly coiled. And they had different anatomical characteristics of the inner ear and jaw that indicated that not only could these fossil bats fly, they could also echolocate.

• 6:20Flora Lichtman?

  So, that's old. Echolocation is old, is what I'm hearing.

• 6:23Speaker 01

  Echolocation is old. And what we ended up finding, so previously, when you make these evolutionary trees using just genomes, it was very difficult to put the fossil data in there, because you can't get DNA out of a fossil that's 65 million years old, or 55 million years old, 45 million years old, and so forth. What you can do is, you can look at their anatomical characteristics, the shape of their bones, the size of their teeth, and you can make then a kind of a data set out of anatomical morphological data, is what it's called. But we hadn't got the tools in the past to integrate that genome data that we're using to make the tree with this weird anatomical data. And that meant that we couldn't really place where did these fossil bats go in this evolutionary

• 7:08Speaker 01

  tree. But using new tools, Liliana Davalos and her team, we're able to integrate this in a really meaningful way.

• 7:15Flora Lichtman?

  So, when you're doing that, do you have to decide where to draw the line? Like, this is a bat and this is not a bat? How do you make that call?

• 7:25Speaker 01

  So, the people that make that call are the brilliant team of paleontologists that we had. And there's key diagnostic characteristics to indicate that these were bats. Wings, shape of, where we had fuller fossils, wings, shape of teeth, diagnostic characters that indicate that they're bats. But you ask a brilliant question, because we're still looking for the kind of ancestral, what is really, what does the proto, the pre-bat look like? And they're this type of transition fossils. And so, we're still trying to, there's a whole bunch of different, potentially proto-bats out there, that we're trying to understand their anatomical characteristics a bit more.

• 8:07Flora Lichtman?

  I know that you, I mean, you've made bats, you know, they're, they must be a huge part of your life. Like, do you feel like you're at this sort of watershed moment where you're about to uncover all these secrets that you've been hunting for, for a long time?

• 8:19Speaker 01

  I'd like to think so, yes. But as a scientist, you think you're right there, you think you've found it, you think you know the answer, and then something mad happens. The more, the more you look, the more you know, the more you realize you don't know. We've been, you know, we've been studying aging in these long-lived bat populations for now 15, 20 years, and we're right there, we're on the tip, but you still need to refine and refine and refine. But this study is a really great step forward in the right direction. So, we're not just looking at their aging or their immunity. We're also looking at their conservation status. Some amazing teams, part of the Bat1K group, they're looking at, can you look within these bat genomes and see evidence of the fact they may be going into genomic decline or

• 9:04Speaker 01

  not? Another group here is looking at how, so if they evolved echolocation, their ability to fly and orient using sound, was there a loss to their vision? What about their olfaction? How does things change? Our research groups are looking at bats that feed purely on nectar versus bats that feed purely on insects. What are the changes that happen within their genomes? And we're also looking at really, I mean, their unique immune responses. How can they live with all these viruses and not get sick? What's going on with their ability to control tumors?

• 9:42Speaker 01

  So, this research has sparked so much more questions that, hopefully, the world is trying to answer.

• 9:51Flora Lichtman?

  Does the sort of immense diversity of bats make your research harder or easier?

• 9:56Speaker 01

  It's a really good question. It makes it harder, because I'm going to have to live an awful long time to sequence the genome of every single living bat, because we keep on finding more species. So, that just makes it harder. It makes it easier, in some ways, because already the experiments that typically would be done in a lab to understand adaptations, the molecular basis of adaptation, have already been done for us. You've got long-lived bats and shorter-lived bats. You've bats that feed on blood are vampires. It is near Halloween, we've got to talk about them. You've got bats that feed on insects. We have a whole metabolic change that's happened within just a single family of bats, for example, the Phylostomates, that if we can sequence their genome and understand their

• 10:41Speaker 01

  diversity, that will allow us, I suppose, decipher, you know, Evolution's notebook of 15 to 55 million years of change. So, it's a good thing. And the other reason why it's a good thing, it means that we have to work with people from all around the globe, because they're found everywhere. And so, they're very unique, I mean, the vampire bats are found in the South Americas. If you want to understand that, we have to be able, really, make bat research global. And that's what Bat1K does, and that's what a lot of these new genome sequencing groups are. The science has to happen across the entire globe for us to be able to understand these unique traits that bats have. And that's the benefit of having so many. The difficulty means that we're going to have to keep going. We need lots more people and lots more money.

• 11:26Flora Lichtman?

  Well, Emma, good luck, and please come back and talk to us when you find more things out.

• 11:33Speaker 01

  Absolutely, Flora. Lovely talking to you.

• 11:35Flora Lichtman?

  Dr. Emma Teeling is a professor of zoology at University College Dublin and co-founder of the Bat1K Global Bat Genome Sequencing Consortium. Thanks again.

• 11:45Speaker 01

  Thanks, Flora.

• 11:54Flora Lichtman?

  And we cannot wrap without plugging the Science Friday Halloween Costume Contest. Show us a pic of you in your spookiest, science-iest costume for a chance to win cool prizes. ScienceFriday.com/Halloween is where you should go. Submit by Sunday. This episode was produced by Charles Berquist. Thank you for listening. I'm Flora Lichtman.