Iguanas Floated One-Fifth of the Way Around the World to Colonize Fiji, Genetic Analysis Indicates
taylorvich writes:
https://phys.org/news/2025-03-iguanas-world-colonize-fiji-genetic.html
Iguanas have often been spotted rafting around the Caribbean on vegetation and, ages ago, evidently caught a 600-mile ride from Central America to colonize the Galapagos Islands. But for long-distance travel, the Fiji iguanas can't be touched.
A new analysis conducted by biologists at the University of California, Berkeley, and the University of San Francisco (USF) suggests that sometime after about 34 million years ago, Fiji iguanas landed on the isolated group of South Pacific islands after voyaging 5,000 miles from the western coast of North America-the longest known transoceanic dispersal of any terrestrial vertebrate.
Overwater dispersal is the main way newly formed islands get populated by plants and animals, including humans, often leading to the evolution of new species and entirely new ecosystems. Understanding how these colonizations happen has fascinated scientists since the time of Charles Darwin, the originator of the theory of evolution by natural selection.
The new analysis, published in the journal Proceedings of the National Academy of Sciences, suggests that the arrival of the ancestors of the Fiji iguanas coincided with the formation of these volcanic islands.
The estimated time of arrival, 34 million years ago or more recently, is based on the timing of the genetic divergence of the Fiji iguanas, Brachylophus, from their closest relatives, the North American desert iguanas, Dipsosaurus.
Previously, biologists had proposed that Fiji iguanas may have descended from an older lineage that was more widespread around the Pacific but has since died out, leaving Brachylophus as the sole iguanids in the western Pacific Ocean. Another option was that the iguanas hitchhiked from tropical parts of South America and then through Antarctica or even Australia, though there is no genetic or fossil evidence to support this.
The new analysis puts those theories to rest.
"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," said lead author Simon Scarpetta, a herpetologist and paleontologist who is a former postdoctoral fellow at UC Berkeley and is now an assistant professor at USF in the Department of Environmental Science.
"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 timeframe, 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."
More information: Simon G. Scarpetta et al, Iguanas rafted more than 8,000 km from North America to Fiji, Proceedings of the National Academy of Sciences (2025). DOI: 10.1073/pnas.2318622122.
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