Millions of years ago, a group of adventurous iguanas did something no one expected. They crossed the Pacific Ocean from the Americas to the islands of Fiji on giant rafts of vegetation.
The iguanas in Fiji and Tonga have always been an evolutionary puzzle. Iguanas are native to the Americas and the Caribbean, but somehow millions of years ago, a small group of them made it all the way to Fiji. There was never land bridge between the two distant places. So how on Earth did they get there?
Evolutionary biologist Simon Scarpetta of the University of San Francisco and his colleagues think they have solved the mystery. They believe the reptiles caught a lift across the ocean on a platform of trees, plants, or debris. These rafts occasionally break off from coastlines and drift out to sea as floating islands. Animals on them may wind up in new and unexpected destinations. In the case of the Fijian iguanas, researchers believe they made a record-breaking trip by drifting over 8,000km across the Pacific Ocean.
“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 told The New York Times.
Fijian iguana. Photo: Shutterstock
Masters of survival
It is quite rare for vertebrates to survive such trips. But iguanas can go weeks without food or fresh water, making them well-suited for long voyages of deprivation. They have been seen rafting before, but their journeys have never been this long. In 1995, a group of about 15 iguanas were spotted hitching a ride 320km between Caribbean islands aboard hurricane debris. The team thinks their slow metabolism and rainwater allowed them to survive the incredibly long journey to Fiji.
There have long been two hypotheses about these out-of-place reptiles. First, that they rafted over from the Americas; and second, that a now-extinct ancestor drifted over from Asia or Australia.
Scarpetta and his team studied the evolutionary history of over 200 species of iguanas and lizards. The four species in Fiji are most closely related to the desert iguanas of Mexico and the American Southwest. That is clearly where they came from, although the timing of their great voyage remains uncertain.
“This suggests that as soon as land appeared where Fiji now resides, these iguanas may have colonized it,” Scarpetta said. “Regardless of the actual timing of dispersal, the event itself was spectacular.”
