Most iguanas are indigenous to the Americas. So how did the Fijian species end up on the island, nearly 5000 miles away in the South Pacific? According to a new study in the journal PNAS, it was probably via raft ... that is, on clump of floating trees. And this rafting hypothesis isn't entirely unprecedented. After hurricanes Luis and Marilyn hit the Caribbean in the 1990s, researchers found that a group of iguanas had floated over 180 miles away from Guadeloupe to the territory of Anguilla. Want to hear more about iguanas? Or rafts? Or evolutionary biology? Email us at [email protected] to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy
Chapter 1: Who are the hosts of this episode?
You're listening to Shortwave from NPR. Hey Shore Wavers, Regina Barber here. And today I'm joined by NPR's Jonathan Lambert. Hey, Jon.
Hey, Gina.
So today you're bringing us a story that you say is sort of like half mystery, half swashbuckling adventure.
Yes, it's seafaring, exploration, intrigue.
Oh my gosh, this is giving me very like One Piece vibes. Okay.
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Chapter 2: What mystery surrounds the iguanas on Fiji?
And on top of all of that, it's about iguanas. Specifically, iguanas native to the tropical island of Fiji. And how they got to this super isolated island has always been a bit of a mystery.
Why was it a mystery?
So most iguanas are native to the Americas, with some in the Caribbean and some on the Galapagos Islands. Fiji is like one-fifth of the way around the globe. And while some iguanas can swim, they can't swim that far.
Okay, so how did these land-bound lizards wind up all the way across the Pacific?
According to a new paper, they floated.
What? What did they float on?
Likely some big clump of downed trees and other vegetation that became a raft of sorts.
Okay, okay.
This new study argues that some intrepid, well, probably inadvertently intrepid, group of iguanas set off from North America to float like 5,000 miles away to reach the island of Fiji.
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Chapter 3: Why is the origin of Fijian iguanas puzzling to scientists?
The iguanas that live on Fiji were most closely related to a group of iguanas that I knew very well from the United States called desert iguanas.
Wait, desert iguanas?
Yeah, the kind that currently lives in the southwestern U.S.
Wow.
And they estimated that these iguanas split a little over 30 million years ago. Now, that timeline doesn't quite line up with the land bridge idea because such bridges would have been either underwater or covered in ice or just too cold for cold-blooded lizards at the time. So there would have been no way for iguanas to walk there.
OK, cool. Tell me more.
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Chapter 4: What are the hypotheses for how iguanas reached Fiji?
Yeah. So it's also around the same time that Fiji itself formed from an underwater volcano.
Yeah.
And so to Scarpetta, that all suggests that at some point in the last 30 million years, some small group of iguanas just so happened to be on some raft of vegetation. And that raft drifted all the way to Fiji.
Wow. OK, so this sounds so wild to me. Like, has anything like this ever been observed before? Like, is this idea of like land animals floating on a raft just some like idea biologists had or has it been observed?
Both. Biologists have long surmised that animals on islands could have gotten there by floating. But people have also actually seen it happen. In 1995, combined hurricanes hit the Caribbean. Here's a clip from the Weather Channel documenting the damage.
Homes were torn apart and airplanes tossed aside and towers toppled. At least three people are reported dead.
Wrecked buildings, fallen trees, and apparently displaced animals. Because in the aftermath of these hurricanes, researchers tracked a group of iguanas that floated on a raft of downed trees over 180 miles from the Caribbean island of Guadalupe to Anguilla.
Wow. OK, but Fiji is like way further away. This still seems really surprising.
It is still really surprising.
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Chapter 5: How do scientists use genetics to trace iguana origins?
Chapter 6: What is the rafting hypothesis for iguana dispersal?
Chapter 7: How far did the iguanas likely travel to reach Fiji?
Okay, so how did these land-bound lizards wind up all the way across the Pacific?
According to a new paper, they floated.
What? What did they float on?
Likely some big clump of downed trees and other vegetation that became a raft of sorts.
Okay, okay.
This new study argues that some intrepid, well, probably inadvertently intrepid, group of iguanas set off from North America to float like 5,000 miles away to reach the island of Fiji.
That is so far.
Yeah, it's wild. Biologists call this kind of journey where an animal travels to a new place and sets up permanent camp a dispersal event. And this would be the longest known trans-oceanic dispersal event of any land animal, except for humans.
Wow. Okay, so today on the show, how scientists figured out the Fijian iguana origin story.
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Chapter 8: What new evidence supports the rafting theory?
I don't usually read a paper and go, wow, that's a surprise. But I did do that when I was reading this one. You know, it just seems like that was the most difficult path in a way.
I mean, I agree. It sounds really, really difficult.
Yeah, these iguanas had so much going against them. It's really, really far, like 5,000 miles of floating across the vast wasteland of the Pacific.
Wow.
No fresh water, the beating sun.
It just brings to mind the images of Tom Hanks in Castaway and he's kind of like surviving there. Yeah. With Wilson and struggling and just thinking about like lizards not only surviving these journeys, but also establishing themselves in a new place. And how long did this journey take? Like months, I imagine.
Yeah, so they don't know for sure, but some previous estimates have ranged from like two and a half months to four months or maybe even longer. And that's a really long time, but both Scarpetta and Villanueva told me that if any creature could do it, it's iguanas. And remember, it's not just any iguanas.
It's desert iguanas. Yes. They seem to love to sunbathe really extra compared to other iguana species.
So they could have been totally fine in the sun. And they can also survive a really long time without fresh water or food.
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