Iguanas are prehistoric-looking lizards that are native to the Americas, the Galápagos Islands, the Caribbean and – 5000 miles away, on the other side of the Pacific – Fiji and Tonga.
There have been many theories about how iguanas ended up in Fiji and Tonga. One theory is that ancient iguana populations hopped from South America to Antarctica before, eventually, making it to Fiji and Tonga. Another suggests that they crossed from North America to Asia before dispersing south onto the Pacific islands.
A new study, however, has found that what actually happened is a whole lot wilder.
DNA and fossils
Professor Simon Scarpetta and colleagues sequenced DNA from 14 iguana species, and used these sequences to build an iguana family tree. What this tree showed is that Fijian iguanas are most closely related to the desert iguanas of North America.
By looking at the differences between the Fijian iguanas’ DNA and the DNA of the North American desert iguana, and by knowing the rate at which DNA changes over time, the team could pinpoint that these species separated around 30 million years ago.
Combining these findings with the fossil record, the team conclude that iguanas most likely ended up in Fiji and Tonga because, around 30 million years ago, North American desert iguanas hitched a 5000-mile ride across the Pacific by rafting on debris. When this debris washed up on Fiji’s shores, probably months later, the iguanas made a new home for themselves.
But how could any animal survive such a journey?
“If you had to pick any vertebrate to survive a rafting event across thousands of kilometres of open ocean, iguanas are a great choice,” Professor Scarpetta, lead author of the study, tells BBC Wildlife.
“Iguanas are large, herbivorous, and many living species are resistant to heat, starvation and dehydration. Some iguanas forgo food for months during cold periods of the year.”
So, it could be that the rafting iguanas simply didn’t need sustenance during their grand adventure. Or, it is possible that they rafted on vegetation that would have provided nourishment.
Either way, this was a journey of epic proportions. While many other species have colonised new lands by rafting across seas, we don’t know of any other land-living animal that has made this mammoth migration across the Pacific Ocean.
Main image: Fijian crested iguana, Brachylophus vitiensis. credit: Nicholas Hess.
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