Fiji Iguanas Crossed the Ocean from the Americas Millions of Years Ago todayheadline

How Iguanas Got from North America to Fiji Millions of Years Ago

By Jack Tamisiea edited by Andrea Thompson

With their bright green scales and powder blue and white splotches, Fijian iguanas look right at home on the lush, tropical islands of Fiji, for which they are named. But scientists have long puzzled over how these bulky lizards first reached this remote spot in the South Pacific.

A new analysis of iguana genetics, published on Monday in Proceedings of the National Academy of Sciences USA, supports the hypothesis that these imposing reptiles actually traveled all the way from southwestern North America—covering more than 5,000 miles in one of nature’s greatest known oceanic odysseys.

Iguanas have colonized islands throughout the Caribbean Sea and the Galápagos archipelago. But none of those journeys can compare to their trip to Fiji, an isolated island chain more than 1,600 miles east of Australia.

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Some had speculated that the lizards reached the islands via land bridges as the southern supercontinent, Gondwana, splintered. Others had posited that the iguanas floated on “rafts” of tree branches or other debris from South America, a voyage that would take several months.

To learn more in the new study, the researchers compared the genomes of one of the four iguana species in the genus Brachylophus that are found on Fiji and Tonga with those of several species found in the Americas. Genetic data revealed that the Fijian reptiles were most closely related to iguanas in the genus Dipsosaurus, which are native to the deserts of southwestern North America—more than 5,000 miles distant from Fiji.

The close relationship between Fijian iguanas (some of which are endangered) and desert iguanas surprised biologist Christina De Jesús Villanueva, a member of the iguana specialist group at the International Union for Conservation of Nature, who was not involved in the new study. “A common ancestor between the green iguana [Iguana iguana] and the Galápagos marine iguana [Amblyrhynchus cristatus] would have been my first guess as the predecessor for the Fijian iguanas,” she says. “But nature and evolution keep finding ways to surprise us.”

According to the study’s researchers, the Fijian iguanas evolutionarily diverged from their North American kin between 34 million and 31 million years ago, long after Gondwana broke up, making the rafting hypothesis most likely. The vast stretch of open ocean between North America and Fiji could only have been crossed by floating on mats of vegetation that were swept out to sea. Such a voyage would be the longest oceanic dispersal by any terrestrial vertebrate known to science.

Study co-author Simon Scarpetta, an evolutionary biologist at the University of San Francisco, says many iguanas are resistant to heat and starvation because of their slow metabolism and often get shunted between islands on clumps of vegetation. “If you had to think of a vertebrate group that could survive a rafting event across thousands of kilometers of open ocean,” he says, “iguanas are a great choice.”