Fiji Iguanas' Remarkable Journey: Traversing 8,000 Kilometers on Driftwood
A groundbreaking study suggests that Fiji's unique iguanas, known as Brachylophus, may have made the longest journey ever undertaken by land vertebrates across the ocean, traveling over 8,000 kilometers on driftwood from North America to the remote Fiji Islands. Researchers from the University of San Francisco explored the genetic ties of these iguanas, revealing a fascinating history of migration.
Historically, the origin of Fiji's iguanas has been a subject of debate among scientists, with two primary theories proposed. One theory suggested that these reptiles arrived via driftwood from either South or North America, while another posited that they island-hopped across the Pacific over time. However, substantial evidence had been lacking for either hypothesis until now.
In their research, scientists conducted a comparative analysis of the genomes of Fiji iguanas and 14 other iguana species. This analysis revealed that their closest living relatives are the desert iguanas (Dipsosaurus) native to Mexico and the southwestern United States. Further investigation into genetic differences indicated that the two lineages diverged approximately 34 to 31 million years ago, coinciding with the formation of the volcanic Fiji Islands.
The researchers propose that a natural disaster, such as a storm, might have uprooted trees inhabited by iguanas, allowing them to drift across the ocean. Simulations suggest that a journey from South America to Polynesia could take between 80 to 120 days, and even a longer journey from North America would likely be manageable for modern desert iguanas, which can survive prolonged fasting during winter hibernation.
Importantly, while drifting on vegetation, these iguanas may have had access to food sources, further supporting their survival during the journey. This extraordinary migration is noted as a significant event in the history of terrestrial vertebrates.
Although it has been established that some land vertebrates can cross oceans, such as the ancestors of Caviomorpha and New World monkeys that traveled from Africa to South America, the distance covered by the Fiji iguanas is unprecedented. Previously, it was confirmed that iguanas from the Americas successfully reached the Galápagos Islands and the Caribbean, with one notable instance in 1995 when green iguanas were found on Anguilla after drifting from Guadeloupe.
The current research underscores that the oceanic dispersal of Brachylophus from North America to Fiji represents the largest known oceanic distribution event for terrestrial vertebrates. Interestingly, while island-dwelling iguanas are common, the extreme distance covered by Fiji iguanas is considered a remarkable exception.
Despite their successful adaptation over millions of years in the isolated Pacific Islands, three of the four species of Fiji iguanas are classified as 'critically endangered' by the International Union for Conservation of Nature (IUCN), primarily due to habitat destruction, wildlife trade, and the introduction of invasive species such as rats and cats.