Scientists may have finally figured out how iguanas, which originated in the Americas, reached the remote volcanic islands of Fiji in the South Pacific. Using statistical models incorporating thousands of genes from hundreds of iguanid species, the latest hypothesis is that Fiji’s iguanas (genus Brachylophus) are most closely related to the desert iguanas of the American Southwest and northwestern Mexico, specifically the genus Dipsosaurus, with their divergence occurring over 30 million years ago.
The story of how they reached Fiji may seem far-fetched, but the researchers think it’s the most likely explanation: long-distance travel on rafts of floating vegetation, perhaps the result of trees being blown over in a storm.
The journey, which would have spanned some 5,000 miles (8,000 km) is thought to be the longest overwater dispersal of a terrestrial vertebrate. The idea of iguanas hitching a ride on floating tree trunks and accumulated plants isn’t new, as it’s almost certainly how the reptiles reached various Caribbean islands and even the Galapagos Islands off the coast of Ecuador.
Traveling from the western coast of North America to Fiji would likely have taken two to four months, yet iguanas have multiple adaptations that could have helped them survive the journey. In addition to eating the matted vegetation on their rafts, they would have been able to withstand the high temperatures and limited water supplies. What the researchers don’t yet know, and may never know, is whether the Fijian iguanas made the journey in one dispersal event or "island hopped” across the Pacific; however, no fossils resembling the Fijian iguanas have been found on any other islands.
Next stop, Fiji?
- The Iguanidae family includes around 700 species of iguanids, nearly all of which live in the Americas. The main exceptions are species in the genus Dipsosaurus, native to Fiji and Tonga, all of which are endangered due to factors like habitat loss, predation by rats, and the exotic pet trade.
- The islands of Fiji have only been in existence for around 34 million years, suggesting that the iguanas arrived there relatively soon after their emergence.
- The research, co-authored by herpetologists from the University of San Francisco and UC Berkeley, was published earlier this month in Proceedings of the National Academy of Sciences.
