Iguanas Floated a Whopping 5,000 Miles From North America to Fiji on Rafts of Plants in a Record-Setting Trip, Study Suggests
Since most iguana species live in the Americas, biologists have long debated how they could have arrived on the remote Pacific island in the first place
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Iguanas inhabit tropical, subtropical and desert regions of the Americas—but surprisingly, they’re also found on a few incredibly remote Pacific islands, such as Fiji. Exactly how iguanas could have reached these islands in the first place is a hotly debated topic.
“The question has definitely captured the imagination of scientists and the public alike,” Simon Scarpetta, an evolutionary biologist at the University of San Francisco, tells the New York Times’ Asher Elbein.
Now, Scarpetta and his colleagues have offered an answer to that question, and it involves a record-breaking journey. In a study published Monday in the journal Proceedings of the National Academy of Sciences, they suggest the lizards hitched a 5,000-mile ride on floating vegetation from the western coast of North America within the past 34 million years. That trip would be the longest transoceanic dispersal of any terrestrial vertebrate known to scientists.
“That they reached Fiji directly from North America seems crazy,” study co-author Jimmy McGuire, a biologist at the University of California, Berkeley, says in a statement. “But alternative models involving colonization from adjacent land areas don’t really work for the timeframe.”
After studying the DNA of more than 200 iguana specimens from museum collections worldwide, the team determined that Fiji iguanas, which belong to the genus Brachylophus, are most closely related to the North American desert iguana genus, Dipsosaurus.
The genetic analysis revealed that Brachylophus and Dipsosaurus diverged between 30 million and 34 million years ago. Coincidentally, the volcanic Fiji islands came into existence around 34 million years ago—meaning that a group of Brachylophus ancestors must have completed their transpacific odyssey shortly after. They probably floated on a mass of uprooted trees or other plants.
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“The probable mechanism of dispersal was rafting on a vegetation mat, so iguanas that voyaged from North America to Fiji could have had food from the raft itself on their journey across the Pacific,” Scarpetta tells Gizmodo’s Isaac Schultz, adding that it probably took them between two and a half to four months to make the trip.
But even if food resources ran low, the rafting iguanas would have been resilient. “Iguanas and desert iguanas, in particular, are resistant to starvation and dehydration, so my thought process is, if there had to be any group of vertebrate or any group of lizard that really could make an 8,000-kilometer journey across the Pacific on a mass of vegetation, a desert iguana-like ancestor would be the one,” Scarpetta explains in the statement.
Previous theories suggested the iguanas had rafted from South America, crossed the Bering land bridge to Asia or reached Antarctica before rafting over to Fiji. Researchers had even suggested they were the sole survivors of an ancient iguana lineage that populated more regions of the Pacific.
However, “given what we know now, their [new] result is by far the most strongly supported,” Kevin de Queiroz, a zoologist at the Smithsonian’s National Museum of Natural History who was not involved with the study, tells the Associated Press’ Adithi Ramakrishnan.
The research leaves some unknowns about the reptiles’ journey, such as whether they stopped over on other islands. “One question worth pointing out regarding our study, though it would be difficult to test, is whether iguanas hopped across islands in the Pacific from North America to Fiji, rather than rafting in a single event,” Scarpetta adds to Gizmodo. Though he calls the possibility “intriguing,” he points out that “no fossils of Fijian iguanas are known from anywhere in the Pacific besides Fiji and Tonga, and volcanic islands, of which there are many in the Pacific, can be ephemeral.”
Ultimately, Hamish Spencer, an evolutionary geneticist at the University of Otago in New Zealand who was not involved in the research, tells the New York Times that the study bolsters the suggestion that “long-distance dispersal is far more important in the evolutionary history of many animal groups than had previously been appreciated.”
