How the iguanas traveled from the Americas to Fiji. Lets learn more!

In terms of evolution, the native iguanas of Fiji and Tonga have long been a mystery. All other extant iguana species are found in the Americas, which include the Caribbean, parts of South America, and the southwestern United States. So how did some reptilian transplants end up on two islands in the South Pacific?

In a study published Monday in the Proceedings of the National Academy of Sciences, evolutionary scientist Simon G. Scarpetta and his colleagues contend that the ancestors of Fiji's iguanas crossed on mats of floating plants.

With an estimated 8,000 km of open ocean, it would be the longest journey ever made by a non-human animal.

An incredible undertaking

Long recognized as a way to reach islands, rafting is the term scientists use to describe how small animals can cross oceans on uprooted trees or tangles of plants. But this is usually seen in invertebrates, which because of their small size can survive for a long time in an uprooted tree trunk. Among vertebrates, lizards and snakes seem to be able to raft farther than mammals, possibly due to their slower metabolisms, which allow them to fast for prolonged periods of time.

It has been shown that guana species can make shorter crossings. In 1995, scientists observed at least 15 green iguanas rafting on hurricane debris over 300 kilometers between Caribbean islands.

An amazing task

It has long been known that small animals can raft—a term used by scientists to describe catching a ride across oceans on uprooted trees or tangles of plants—to reach islands. But this is usually seen in invertebrates, which, because of their small size, can survive for a long time in an uprooted tree trunk. Because of their slower metabolisms, which enable them to fast for longer periods of time, lizards and snakes seem to be able to raft farther than mammals among vertebrates.

Shorter crossings have been shown to be possible for guana species. Researchers observed at least 15 green iguanas using hurricane debris to travel more than 300 kilometers between Caribbean islands in 1995.

A formidable obstacle

Small animals have long been known to employ rafting, the term scientists use to describe catching a ride across oceans on uprooted trees or tangles of plants, to get to islands. This is usually seen in invertebrates, which because of their small size can survive for a long time in an uprooted tree trunk. Because of their slower metabolisms, which allow them to fast for longer periods of time, lizards and snakes seem to be able to raft farther than mammals among vertebrates.

It has been shown that certain guana species are adept at shorter crossings. In 1995, scientists observed at least 15 green iguanas rafting nearly 300 kilometers across the Caribbean on hurricane debris from island to island.

After studying the DNA of 14 extant iguana species, researchers discovered that the closest living relatives of the Fijian species are members of the genus Dipsosaurus, which includes desert iguanas found in the American Southwest and northwest Mexico. The two genuses split between 30 and 34 million years ago, the team concluded.

It's all about timing. Around this period, the Fijian archipelago was formed. More importantly, because of the cold and ice around the poles at the time, no lineage of temperature-sensitive iguanas could have hopped to the Pacific islands after traveling from the Americas to Asia or Australia.

Since a three- to four-month journey would have almost exactly matched the length of the critters' winter hibernation, it is possible that the lizards survived the trip without starving, which lends more credence to this theory. If they had been able to move on vegetation, the herbivores would also have had a steady supply of food.

Evolutionary genetecist Hamish G. Spencer of the University of Otago says the discovery adds to the growing body of evidence showing that "long-distance dispersal is significantly more essential in the evolutionary history of many animal species than had previously been realized."