Anglerfish Ancestors Once Roamed The Seafloor

There are over 200 species of deep-sea anglerfish; some are long and thin, some are squat and round, some have fins that they use to "walk" along the sea floor, and others have huge eyes set far back into their heads. But how did all this morphological diversity first come to be? Thanks to a new anglerfish family tree, now we know. Scientists built this evolutionary tree using genetic information from hundreds of samples and anglerfish specimens across the globe. It indicates that anglerfish originated from an ancestor that crawled along the seafloor ... and sheds new light on how experts could think about biodiversity as a whole. 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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• 0:00Speaker 00

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• 0:16Emily Kwong?

  You're listening to Short Wave from NPR. The first time I ever saw an anglerfish was on the big screen. It appeared first as a warm, glowing light. I see a... I see a light.

• 0:33Speaker 02

  A light?

• 0:34Emily Kwong?

  Yeah, over there.

• 0:35Speaker 02

  Oh, I see it too.

• 0:38Emily Kwong?

  Rising out of the dark with bulbous eyes and pointy teeth, this fish gets a villain moment in the 2003 Pixar movie Finding Nemo. It's so pretty.

• 0:51Speaker 02

  Good feelings gone.

• 0:57Emily Kwong?

  And so ensues probably the best underwater chase scene in cinematic history.

• 1:03Speaker 03

  I remember seeing this movie in the theaters. I was three in 2003.

• 1:09Emily Kwong?

  This is Rose Fauchet from Rice University.

• 1:12Speaker 03

  And apparently, when the anglerfish scene came on, I was so freaked out by it, I started crying, and my mom had to take me out of the theater.

• 1:21Emily Kwong?

  But Rose has had a change of heart about anglerfish, because this past year, she did research about them alongside evolutionary biologist and ichthyologist Elizabeth Miller at UC Irvine. Now, Elizabeth says this moment in Finding Nemo, where Dory and Marlin are enthralled by the anglerfish's bioluminescent light, is pretty accurate to how it happens in the deep sea.

• 1:43Speaker 04

  The idea is that the prey are drawn to the lure, and they don't see the anglerfish attached to it, and they get eaten.

• 1:52Emily Kwong?

  There are over 200 species of deep sea anglerfish. The one in Finding Nemo was modeled after what's known as the football fish. But Elizabeth and Rose told me others look very different. Some are long and thin, like eels. Some are squat. Some have huge, prehistoric-looking teeth, while others have big eyes set far back into their heads. And the majority of them live in the Baffy Pelagic Zone, the deep, deep sea.

• 2:21Speaker 04

  It's a huge expanse of space in total darkness. High pressure, cold temperatures, food limitation.

• 2:29Emily Kwong?

  But in this zone, that is so cold, so homogeneous, and so devoid of sunlight, somehow, the anglerfish still ended up looking very diverse. And researchers wanted to know why.

• 2:42Speaker 04

  It is a mystery. It's not clear why one anglerfish species would be shaped one way, while a different anglerfish species would be shaped a different way.

• 2:53Emily Kwong?

  So today on the show, the big anglerfish mystery. Why do these science-fiction-y fish look so different from one another? What spurred this divergence in anglerfish body shape and size? And what can that tell us about the deep sea as a whole? I'm Emily Kwong, and you're listening to Short Wave, the science podcast from NPR.

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• 4:26Emily Kwong?

  All right, Rose and Elizabeth, the deep sea pelagic anglerfish. What were the big question marks for you? And what did you wanna, what did you wanna figure out?

• 4:34Speaker 04

  So we can look at images of anglerfish. And it seems obvious to our eyes that they're different shapes. But we needed to quantify that variation so that we can analyze it in an evolutionary framework. And what I mean by an evolutionary framework is understanding how all of that diversity evolved. Did it evolve very quickly? Did it evolve gradually? Those are the big questions.

• 4:58Emily Kwong?

  And Rose, at the time, you were an undergrad student at Rice University in Elizabeth's colleague's lab. Can you explain what you did on this project? What was your role?

• 5:08Speaker 03

  So my part of the project was looking at the morphology of anglerfish skulls. I had to look at the skeletons of the anglerfish and then determine which bones are which and like the edges of all the bones and things like that. So I took the CT scans that we had of these anglerfish. And first I had to make them into like a 3D model. And then we have this very fun software that basically lets me put a little dot on certain points of that skull model. We settled on, I believe it's 111 landmarks that I put onto each of these skulls.

• 5:53Speaker 04

  Yeah, I will say 111 points is a lot. It's even more difficult when you've got these fish that have such bizarre skulls. The work that Rose did is really tremendous and it was all done by hand.

• 6:06Emily Kwong?

  So you all set about building a family tree for anglerfish.

• 6:12Emily Kwong?

  So cool. How do you even go about building something like that?

• 6:15Speaker 04

  So to back up a little bit, the big family tree is what links all of these species together.

• 6:21Emily Kwong?

  Yeah.

• 6:21Speaker 04

  And the methods to do this are the same for pretty much any organism. You extract DNA from the tissues of these specimens.

• 6:31Emily Kwong?

  Uh huh.

• 6:32Speaker 04

  What makes it difficult in the case of the anglerfish is getting those tissues.

• 6:35Emily Kwong?

  Right, this isn't a 23andMe situation. You can't just ask anglerfish to spit into a tube for you so you can collect their DNA.

• 6:43Speaker 04

  That's correct. And finding the fish is no small feat, as you can imagine. It relies on careful planning of people who regularly go out to sea to do surveys of fishes in general, not necessarily targeting anglerfishes. And making sure when an anglerfish is found that it's preserved in the proper way. It needs to be kept on ice and kept cold pretty much as soon as it's brought up. It needs to be preserved in alcohol and put on a shelf in a museum. And that, that's the basis of the CT scans or the three dimensional X-rays that we used. And then the tissues were the basis of the family tree.

• 7:24Emily Kwong?

  Okay, so while Rose was mapping all these three dimensional X-rays, plotting points onto the skulls to see where the anglerfish were visually similar. It sounds like Elizabeth, you were extracting the DNA and seeing where they were genetically similar.

• 7:37Speaker 04

  That's right, that's exactly right. And so from there, I use fancy statistical models. And basically, it tells me what the differences are from species to species and the significance of those differences as far as like how closely or distantly related the different species are.

• 7:56Emily Kwong?

  Wow, okay. Rose, can you talk a little bit about how you and Elizabeth got access to all these specimens and CT scans? I heard all this was done with museum collections, kind of like... An interlibrary loan but for museums?

• 8:12Speaker 03

  So, all these different museums across the world have like fantastic collections of fish that are basically just preserved in ethanol. And there is like an online database where you can search for, you know, whatever species of fish you're looking for and it will show you. And the, the fish world is actually, it's pretty small. It feels kind of like everybody knows everybody.

• 8:36Emily Kwong?

  Yeah.

• 8:37Speaker 03

  And so if you ask nicely enough, they'll FedEx you fish that have been sitting in a jar since like 1965.

• 8:47Speaker 03

  And if you're a very lucky undergrad, you get to open up a package in lab one day and you're holding like one of the rarest fish on earth.

• 8:55Emily Kwong?

  Uh, were you one of these lucky undergrads who got to do this?

• 8:58Speaker 03

  I did get to be an undergrad who opened up a box from FedEx one day and there's a football fish, you know, wrapped in cheesecloth soaked in ethanol. And I picked up the fish and I was so excited. I ran down the halls of this building to like go and show all of my friends that I had a football fish. Um, also, I'm sure it's, you know, shocking to hear, but, but 60-year-old fish sitting in ethanol do have a particular smell about them.

• 9:31Emily Kwong?

  Delicious. So you are going deep into anglerfish history in a way in looking at these samples. I want to go all the way back to the original anglerfish ancestor. What did that ancestor look like? The one that started it all?

• 9:53Speaker 04

  I'll, I'll give some context that anglerfish, the deep sea anglerfish we've been talking about are all part of this group with a scientific name Lophia formis.

• 10:02Emily Kwong?

  Lophia formis.

• 10:03Speaker 04

  Yes.

• 10:04Emily Kwong?

  Okay.

• 10:04Speaker 04

  So the deep sea anglerfish, their closest relative within this broader group is a fish called the sea toad.

• 10:11Emily Kwong?

  The sea toad?

• 10:12Speaker 04

  Yes. That's another fun one to Google if you, if you have access to Google the, um, sea toad.

• 10:19Emily Kwong?

  Oh, I am, I am. Coffin fishes, is that another word for sea toads? Yeah, they look very grumpy. They're literally frowning.

• 10:26Speaker 04

  Exactly.

• 10:26Emily Kwong?

  And hanging out on the bottom of the ocean floor.

• 10:28Speaker 04

  Yep, coffin fish is another word for them. So that's the closest relative, the closest living relative to the, the deep sea angler fishes we've been talking about. And so what did the direct ancestor of the angler fishes look like? It most likely looked something like that sea toad, although perhaps something intermediate. We, we can't know for sure, but what it implies is that the broader group, Lophiiformes, has always been in the deep sea in some capacity, but the more significant transition was off the seafloor and into the water column.

• 11:02Emily Kwong?

  Yeah. This seems like one of the biggest takeaways of your study, and it's amazing that angler fish started from an ancestor that lived on the ocean floor and then made it into the water column to be the angler fish that we know and love today.

• 11:17Speaker 04

  That's correct. The bathyplagic angler fishes seem to have arisen from a deep sea benthic ancestor, and it was this transition off the seafloor that spurred the evolution of all of these new shapes.

• 11:31Emily Kwong?

  And what does that tell us about, like, the conditions of this part of the ocean that made that so? Like, is it just that they had to adapt super quickly in order to survive?

• 11:41Speaker 04

  I, I think the way to think about it is opportunity. They came off the seafloor into the water column, the bathyplagic zone, and presumably there are new ways of living, new ecological opportunities, even if we don't know necessarily what they are. And so they potentially evolved these new shapes to take advantage of those new opportunities.

• 12:04Emily Kwong?

  Yeah. I want to ask you both one last question. Why do you think this is so important to study? How does it change your, how you think about this field of evolutionary biology?

• 12:15Speaker 04

  I, I think this is critical for our understanding of the conditions that diversity evolves in. We're used to thinking of biodiversity in, in terms of like tropical rainforests and coral reefs, places that have a lot going on. And we look at a place like the deep sea and we see the opposite of that. And what we're learning from the evolutionary history of the anglerfish is that that also might be a place where you can evolve a lot of biodiversity. And that's a totally new way of looking at that environment.

• 12:49Emily Kwong?

  Rose?

• 12:50Speaker 03

  Well, so I think especially natural history and marine biology at this point in time can be a pretty devastating field to work in. You know, so much of what we do and what we think about is how much we are constantly losing. That's already gone.

• 13:16Speaker 03

  But there's something about the scope of this project that felt positive and kind of like a nice reprieve from that.

• 13:25Emily Kwong?

  Yeah.

• 13:26Speaker 03

  I think a lot of this project was celebrating the biodiversity that we do have. And yeah, it's kind of nice to for once not be like, well, here's a thousand genuses about to go extinct.

• 13:41Emily Kwong?

  No, here's a thousand genuses being opportunistic hunters in the ocean.

• 13:46Speaker 03

  Yeah.

• 13:48Emily Kwong?

  I love that. Well, thank you both so much for spending time with me and helping short waivers everywhere learn more about these incredible fish.

• 13:58Speaker 04

  It was my pleasure. Thank you.

• 14:00Speaker 03

  Thanks.

• 14:03Emily Kwong?

  This episode was produced by Hannah Chin. It was edited by Burleigh McCoy and fact checked by Tyler Jones. The audio engineer was Kwesi Lee. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thank you for listening to Short Wave from NPR.