"We found that the Fiji iguanas are most closely related to the North American desert iguanas, something that hadn't been figured out before, and that the lineage of Fiji iguanas split from their sister lineage relatively recently"
Biologists with the University of California, Berkeley and the University of San Francisco have released a research paper saying iguanas migrated on floating platforms of some sort after 34 million years ago, from the west coast of North America to the Fiji islands. That is a journey of about 5,000 miles. This, the researchers say, is the longest “transoceanic dispersal of any terrestrial vertebrate.”
“We found that the Fiji iguanas are most closely related to the North American desert iguanas, something that hadn’t been figured out before, and that the lineage of Fiji iguanas split from their sister lineage relatively recently, much closer to 30 million years ago, either post-dating or at about the same time that there was volcanic activity that could have produced land,” lead author Simon Scarpetta, a herpetologist and paleontologist and former postdoctoral fellow at UC Berkeley said in a statement announcing the findings. Scarpetta is now a Department of Environmental Science assistant professor at University of San Francisco.
Scarpetta’s research suggests the arrival of the ancestors of these lizards took place at the same time as the formation of the volcanic islands that make up the archipelago of more than 330 islands that is called Fiji. The researchers base their timing on the genetic divergence of the Fiji iguanas of the Brachylophus genus with that of their closest relatives, the North American desert iguanas of the genus Dipsosaurus.
A male Central Fijian banded iguana, Brachylophus bulabula, from Ovalau Island, Fiji. Photo by USGS
“That they reached Fiji directly from North America seems crazy,” said co-author Jimmy McGuire, UC Berkeley professor of integrative biology and herpetology curator at the Museum of Vertebrate Zoology. “But alternative models involving colonization from adjacent land areas don’t really work for the time frame, since we know that they arrived in Fiji within the last 34 million years or so. This suggests that as soon as land appeared where Fiji now resides, these iguanas may have colonized it. Regardless of the actual timing of dispersal, the event itself was spectacular.”
While it is not known how these lizards rafted 5,000 miles from North America, the researchers do have some theories. “You could imagine some kind of cyclone knocking over trees where there were a bunch of iguanas and maybe their eggs, and then they caught the ocean currents and rafted over,” Scarpetta said.
Previous research based on a few fossils found in east Asia led to speculation that the ancestral population of iguanids lived around the Pacific Rim and island hopped into the middle of the Pacific Ocean. Other previous speculation had the reptiles making the trek by the Bering Land Bridge into Indonesia and Australia, or down the Pacific coast of North America and through Antartica.
Scarpetta’s research involved collecting genome wide sequence DNA from more than 4,000 genes and tissues that involved more than 200 iguanid specimens. These specimens were housed in museum collections worldwide. When Scarpetta looked at the data he collected, one thing stood out from the rest. Scarpetta noticed that the Fiji iguanas are more closely related to the North American desert iguanas. No other lizard in the genus came close.
The desert iguana (Dipsosaurus dorsalis) is a Zone 3 reptile, a partial or open sun basker. Photo by Milan Zygmunt/Shutterstock
“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 said in the press release.
Scarpetta was supported by Robert Fisher of the U.S. Geological Survey in San Diego, Benjamin Karin and Ammon Corl of UC Berkeley, Jone Niukula of NatureFiji-MareqetiViti in Suva and Todd Jackman of Villanova University in Pennsylvania. He was also supported by a National Science Foundation postdoctoral research fellowship.
An abstract of the paper, “Iguanas rafted more than 8,000 km from North America to Fiji” can be read on the Proceedings of the National Academy of Sciences of the United States website.
