Did you know that iguanas undertook one of the longest known overwater migrations from America to Fiji?

For decades, scientists have been puzzled over the origins of Fiji's native iguanas. Unlike all other living iguana species, which are native to the Americas, these reptiles live in the remote South Pacific islands of Fiji and Tonga. But the question remains, how did these iguanas that are a part of the distinct Brachylophus genus, come to inhabit these islands?
A study published in the Proceedings of the National Academy of Sciences gives a surprising explanation. Researchers, led by Simon G. Scarpetta, an evolutionary biologist from the University of San Francisco, have proposed that the ancestors of these iguanas reached the islands travelling on mats of floating vegetation. This journey, spanning nearly 8,000 kilometers of open ocean, is thought to be the longest known overwater migration by any non-human vertebrate.
The theory of "rafting", where species travel across oceans on floating vegetation or debris, is not new, especially among invertebrates. Small creatures like insects or marine invertebrates often use such methods to reach distant islands. However, for larger animals like lizards, such long oceanic voyages have been considered incredibly difficult and full of challenges. While some species of iguanas and other reptiles have been known to cross shorter distances by floating on debris, the idea that the ancestors of Fijian iguanas could have made a nearly 8,000 km journey across the Pacific has been widely debated.

Scarpetta and his team’s study adds new information to the rafting theory by focusing on the genetic history of Fijian iguanas. By studying genetic samples from 14 different iguana species, the team found that Fijian iguanas share a common ancestor with desert iguanas from the American Southwest.
The split between these two lineages is estimated to have occurred around 30 to 34 million years ago, which is a similar period coinciding with the formation of the Fijian archipelago. This timing suggests that the iguanas did not arrive by land, as some have speculated, since the Earth’s climate at the time made such a land route impossible for cold-blooded reptiles.

This genetic evidence supports the idea that overwater rafting was the most plausible route for the iguanas' arrival. Scarpetta’s team pointed out that the crossing would have taken about three to four months, a time span that fits within the iguanas’ hibernation period. This extended journey might have been manageable because the iguanas could have survived by feeding on the vegetation they were traveling on, which would have sustained them during the voyage.
The discovery talks of the fascinating ways in which animals have managed to populate the most remote corners of the Earth, bringing to light the hidden mechanisms of evolution and survival in nature.