Iguanas on the remote islands of Fiji may appear to live chill lives, but according to new research they had to work for it: by floating across thousands of miles of ocean on vegetation in the last 30 million years or so.
That’s right. A new investigation of the Iguanidae family tree—a tree that includes some 2,100 reptilian species, from the marine iguanas of the Galapagos to chameleons of the tropics and chuckwallas of the desert—indicates that Fiji iguanas are most closely related to lizards in the American Southwest.
Given the vast geographic distance between the two but their relative genetic proximity, a team of researchers concludes that, in the ancient past, a group of desert reptiles hitched a ride on floating debris and never looked back—somehow making it to Fiji and surviving there for about 34 million years. The team’s research was published today in Proceedings of the National Academy of Sciences.
“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 Simon Scarpetta, a herpetologist and paleontologist at the University of San Francisco and lead author of the paper, in a University of California, Berkeley release.
“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 told Gizmodo in an email. “They were also likely resilient to the conditions they faced on the way, such as lack of standing water and high temperatures.” As for timeline, Scarpetta said previous estimates for a trans-Pacific journey were between 4 to 12 months, though more recent simulations suggested a timeline of 2.5 to 4 months.
If the team’s conclusions are correct, the ancestors of Fiji iguanas schlepped a staggering 5,000 miles (8,047 kilometers) from western North America to Fiji, riding on vegetative flotsam, fortuitous ocean currents, and a dream. That commute would be the longest-known transoceanic dispersal of a terrestrial vertebrate—an oddly specific record, but one that speaks to the superlative nature of the finding.
“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.
A genetic analysis of more than 4,000 iguana genes, taken from more than 200 specimens of the lizards, revealed the Fiji iguana’s closest relatives: the North American desert iguana (Dipsosaurus dorsalis).
Because Fiji’s islands formed about 34 million years ago, and based on the timing of the Fiji iguanas’ genetic divergence from the North American desert iguanas, the researchers think the lizards arrived on the island in the last 30-odd-million years.
“That they reached Fiji directly from North America seems crazy,” said co-author Jimmy McGuire, a herpetologist at UC Berkeley, in the same release, “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.”
The notion that iguanas floated from elsewhere to the islands of the South Pacific has previously been, erm, floated. But the new research effectively rules out a South American origin for the Pacific iguanas, as well as the notion that the reptiles evolved from an older lineage that was widespread in the Pacific before going extinct.
“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 added. “This is an intriguing possibility, though 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.”
Despite being isolated on remote islands, the four species of iguana on Fiji and Tonga are endangered due to a combination of habitat loss, predation, and the exotic pet trade. The new research is a reminder of the pains living things have endured to survive, and gives us another reason to conserve the animals that have made it to today.
