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| A Fijian crested iguana (Brachylophus vitiensis) resting on a coconut palm on the island of Fiji in the South Pacific. The four species of iguanas that inhabit Fiji and Tonga today are descended from ancestors that colonized the island within the past 34 million years, probably by rafting 5,000 miles across the Pacific Ocean from western North America. in Scarpetta, Fisher, Karin, Niukula, Corl, Jackman et McGuire, 2025. |
Abstract
Founder-event speciation can occur when one or more organisms colonize a distant, unoccupied area via long-distance dispersal, leading to the evolution of a new species lineage. Species radiations established by long-distance, and especially transoceanic, dispersal can cause substantial shifts in regional biodiversity. Here, we investigate the occurrence and timing of the greatest known long-distance oceanic dispersal event in the history of terrestrial vertebrates—the rafting of iguanas from North America to Fiji. Iguanas are large-bodied herbivores that are well-known overwater dispersers, including species that colonized the Caribbean and the Galápagos islands. However, the origin of Fijian iguanas had not been comprehensively tested. We estimated the phylogenetic relationships and evolutionary timescale of the iguanid lizard radiation using genome-wide exons and ultraconserved elements (UCEs). Those data indicate that the closest living relative of extant Fijian iguanas is the North American desert iguana and that the two taxa likely diverged during the late Paleogene near or after the onset of volcanism that produced the Fijian archipelago. Biogeographic models estimate North America as the most probable ancestral range of Fijian iguanas. Our analyses support the hypothesis that iguanas reached Fiji via an extraordinary oceanic dispersal event from western North America, and which spanned a fifth of the earth’s circumference (>8,000 km). Overwater rafting of iguanas from North America to Fiji strengthens the importance of founder-event speciation in the diversification of iguanids and elucidates the scope of long-distance dispersal across terrestrial vertebrates.
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| A Fijian crested iguana (Brachylophus vitiensis) resting on a coconut palm on the island of Fiji in the South Pacific. The four species of iguanas that inhabit Fiji and Tonga today are descended from ancestors that colonized the island within the past 34 million years, probably by rafting 5,000 miles across the Pacific Ocean from western North America. photo: Nicholas Hess |
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| A map of the world 34 million years ago, showing hypothesized scenarios for the colonization of Fiji by Brachylophus. Based on new research, the most likely scenario is represented by the dark blue arrow from western North America to Fiji. The small red stars represent sites in North America where fossil iguanids have been found. The ranges of modern iguanids — in the Americas and Fiji and Tonga — are shown in light blue. |
Simon G. Scarpetta, Robert N. Fisher, Benjamin R. Karin, Jone B. Niukula, Ammon Corl, Todd R. Jackman and Jimmy A. McGuire. 2025. Iguanas rafted more than 8,000 km from North America to Fiji. Proceedings of the National Academy of Sciences. 122 (12) e2318622122. DOI: doi.org/10.1073/pnas.2318622122 [March 17, 2025]
Iguanas floated to Fiji millions of years ago on an unprecedented raft journey, scientists say
https://www.universityofcalifornia.edu/news/iguanas-floated-fiji-millions-years-ago-unprecedented-raft-journey-scientists-say
Significance: Transoceanic dispersal to far-away islands is an important mechanism for the generation of new species lineages and biotas and has captivated scientists since at least the time of Darwin. Determining whether and how such events occur is challenging, particularly for hypothesized dispersals spanning thousands of kilometers. We addressed the enigmatic occurrence of Fijian iguanas via phylogenomic and biogeographic analyses, providing strong evidence that iguanas rafted >8,000 km from North America as early as the Paleogene. This represents the longest documented transoceanic dispersal in terrestrial vertebrates. Our findings elaborate on the importance of long-distance dispersal in the diversification of iguanids. Iguanid lizards display a propensity for overwater dispersal, which could stimulate further research into the predictability of these incredible biogeographic events.
