You’ll often hear the phrase “wind, wave or wing” to explain how species arrived on islands in the Pacific.
Here in Hawai’i, it is believed ferns arrived when their spores blew in from the wind. And did you know scientists think the native land snails, the kāhuli, were likely first brought to Hawaiʻi by birds?
Throughout the Pacific, these evolutionary mysteries still persist. A new study tracks down where native iguanas in Fiji and an extinct species from Tonga came from, offering clues about the ecosystems of volcanic islands.
University of San Francisco evolutionary biologist and herpetologist Simon Scarpetta said that some scientists hypothesize two main thoughts on how iguanas showed up on the remote islands of Fiji and Tonga.
"When Western scientists first saw these iguanas, I think they were confused about exactly what they were, because it seems really weird that you would have something that seemed to be so similar to the iguanas of the Western Hemisphere all the way over in Fiji… Maybe there was a dispersal event, although we're not really sure how or when that would have happened, or what, that would have looked like," Scarpetta said.
"So some other scientists had the other idea that, well, maybe then, instead of iguanas coming from the Americas, maybe iguanas had always been in the Eastern Hemisphere ancestrally, and so maybe they came through Australia or through Southeast Asia, or potentially even Antarctica or something like that and then, later on, went extinct in the Eastern Hemisphere. And so those were kind of the two main ideas that there were beforehand."
Through phylogenomics — using DNA sequences to analyze how species are related — Scarpetta expanded on a data set that his colleagues previously developed.
“It ended up being those data that they built and that we further developed that were really, really key to figuring out with very, very good support and good certainty that Fijian iguanas and desert iguanas were each other's closest relatives," he told HPR.
The study found "strong evidence" that iguanas rafted thousands of miles from North America tens of millions of years ago.
He said further evidence suggests that the iguanas were able to use a mat of vegetation, such as a tree or plant knocked down from land and into the water, as a “raft” to go from one place to another.
“All the living species of iguanas, well over half of them are found on islands. There's definitely something that appears to predispose them, not only to be able to raft, but then also to be successful at rafting too, to be able to establish on arrival and to be able to even survive the journey," he said. "If you had to pick any particular group of lizard or any animal that could really make a journey like that and actually happen, iguanas may be the one."
Scarpetta's research into Fijian iguanas was published in the journal "Proceedings of the National Academy of Sciences."
This interview aired on The Conversation on March 24, 2025. The Conversation airs weekdays at 11 a.m.
