Island-dwelling Iguanas First Arrived in Fiji by Rafting Across 5000 Miles of Open Ocean
Featured image Caption: Iguanas in the genus Brachylophus, which are native to Fiji and surrounding islands, are proposed to have arrived in the area following a 5000-mile dispersal event crossing the Pacific Ocean from western North America. (Image source: ‘Central Fijian Banded Iguana’ by nasiko, CC-BY-NC 4.0, via iNaturalist)
Source article: Simon G. Scarpetta, Robert N. Fisher, Benjamin R. Karin, Jone B. Niukula, Ammon Corl, Todd R. Jackman, Jimmy A. McGuire. Iguanas rafted more than 8,000 km from North America to Fiji. Proceedings of the National Academy of Sciences, 2025; 122 (12) DOI: 10.1073/pnas.2318622122
Cowabunga! Research reveals iguanas surfed their way to Fiji
When you think of animal movement, you might picture a herd of stampeding gazelles, the seasonal migration of songbirds, or the bumbling of pollinators on a warm day. Researchers at UC Berkeley and University of San Francisco propose an addition to this mental image: surfing iguanas.
The family Iguanidae contains the well-known green iguana of Central and South America, along with 44 other species spread across tropical regions including the Caribbean, the Galápagos, and even the deserts of the American Southwest. However, one lineage stands out for its geographic isolation – Fiji iguanas. These vibrant, tree-dwelling reptiles live thousands of miles from their nearest relatives, raising a fundamental question: how did they get there?
From deserts to deserted islands: Fiji iguanas are closely related to North American desert iguanas
To solve this mystery, researchers analyzed DNA across a wide group of iguana species and constructed a phylogenetic tree to determine their evolutionary relationships. Previous attempts to determine how the Fiji iguanas fit into this group were inconclusive, and based on only a few genes. To build a more robust picture, the researchers sampled more than 200 museum specimens of iguanas and considered over 4000 genes in their analysis.
Surprisingly, researchers found that Fiji iguanas (genus Brachylophus) are most closely related to North American desert iguanas (Dipsosaurus), rather than iguanas from South America or other Pacific islands. Genetic analysis suggests these lineages diverged around 34 million years ago – coinciding with the volcanic formation of the Fiji Islands. This discovery ruled out earlier theories that Fiji iguanas descended from a now-extinct Pacific ancestor.
Several migration routes were proposed to explain how Fiji’s iguanas arrived from western North America, including a path along the northern edge of the Pacific Ocean through Asia or a southern route via South America and Antarctica. While these options seemed reasonable because of the reduced ocean-rafting distance, neither possibility is supported by fossil or genetic evidence. Instead, the only scenario consistent with both the genetic data and Fiji’s geological history was a direct, long-distance transoceanic rafting event. While such a journey would leave no fossil record – as floating iguanas would not be preserved in sediment – DNA evidence strongly supports this extraordinary migration.
Radical Reptiles: How iguanas shredded waves to Fiji
Iguanas are not typically thought of as ocean travelers, yet they have been observed rafting on floating debris in the Caribbean and have even crossed the 600-mile expanse between mainland Ecuador and the Galápagos Islands. After extreme weather events such as hurricanes or cyclones, tree trunks and vegetation mats can break free and drift across the ocean, sometimes carrying unexpected passengers. Iguanas, being strong swimmers and able to survive long periods without food or water, are well-suited for this kind of journey.
The idea that a group of iguanas could survive a 5,000-mile rafting voyage from North America to Fiji may seem improbable, but their physiology offers them some protections. Since they are cold-blooded, iguanas do not need to generate their own body heat, allowing them to conserve energy for extended periods. Additionally, as herbivores, they could sustain themselves by feeding on the vegetation of their makeshift rafts. And, as the genetic evidence suggests, if the original iguanas to make this journey were closely related to desert iguanas, they may have also had the ability to withstand extended periods of little food and water better than iguanas originating from a more tropical locale.
Hang Ten (Million Years): The impact of rare dispersal events on evolution
Today, only four of five known species of Brachylophus iguanas remain, inhabiting Fiji. Their existence is a testament to the important role that rare dispersal events play in shaping biodiversity. While long-distance dispersal is infrequent, when it does occur it can establish entirely new populations and influence evolutionary trajectories in dramatic ways.
Islands provide natural laboratories for studying evolution, as species that manage to reach them often evolve in isolation, adapting to their unique environments. This phenomenon, known as the founder effect, occurs when a small group of individuals colonizes a new area, carrying only a fraction of the genetic diversity of their original population. Over generations, natural selection and other chance events shape these isolated populations, sometimes leading to rapid divergence and the emergence of entirely new species. This process has given rise to many of the world’s most distinctive island-dwelling organisms, from the giant tortoises of the Galápagos to the unusual flightless birds of New Zealand.
The journey of Fiji’s iguanas represents the longest-known overwater dispersal event for a terrestrial vertebrate. Their story not only rewrites their evolutionary history but also offers broader insights into how life colonizes remote islands. It highlights the importance of rare yet impactful migration events in shaping the natural world – sometimes, all it takes is the right storm, the right raft, and a little reptilian resilience to create a whole new chapter in evolutionary history.
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