A groundbreaking study published in the Proceedings of the National Academy of Sciences has unveiled new insights into the origins of Fiji’s iguana species. According to the research, approximately 34 million years ago, iguanas embarked on an extraordinary 5,000-mile journey from western North America to the islands of Fiji. This discovery highlights what may be the longest known transoceanic migration of any terrestrial vertebrate.
The Longest Known Terrestrial Dispersal
The study, led by herpetologist and paleontologist Simon Scarpetta, suggests that Fiji’s native iguanas, Brachylophus, are most closely related to North American desert iguanas, Dipsosaurus. This connection had not been established before. Scarpetta, now an assistant professor at the University of South Florida, explained in a press release that this revelation significantly alters previous assumptions about the origins of Fiji’s iguana species.
“Prior research had suggested that Fiji’s iguanas were descendants of a now-extinct species, but our findings tell a different story,” Scarpetta said.
Iguanas and Overwater Dispersal
Overwater dispersal, the process by which organisms travel across seas to new landmasses, is a well-documented phenomenon. Species ranging from plants to animals, including humans, have used this natural mode of travel to colonize newly formed islands. This dispersal process has fascinated scientists, including Charles Darwin, for centuries as it leads to the development of unique ecosystems and species.
Iguanas, found across the globe, often occupy isolated regions such as the Galapagos and Fiji. The new research challenges earlier hypotheses about the arrival of Fiji’s iguanas, which were once thought to have descended from a now-extinct species. Instead, the study suggests the iguanas arrived via a transoceanic journey, coinciding with the formation of the Fiji archipelago.
Genetic Evidence of the Journey
Through a detailed analysis of genetic divergence, the study reveals that the Fiji iguanas split from their closest relative, the desert iguana, around 30 to 34 million years ago. This timing aligns closely with volcanic activity in the region, which could have created the land masses of the Fiji islands.
“The lineage of Fiji iguanas diverged much more recently than previously thought, coinciding with or just after volcanic events that may have created land in the region,” Scarpetta noted.
While other theories have suggested the iguanas may have come from South America or Australia, no fossil evidence supports these claims. Scarpetta posits that a large storm could have swept the iguanas out to sea, with the creatures surviving the journey due to their ability to withstand extended periods without food or water.
“It’s plausible that a cyclone could have knocked over trees where iguanas and their eggs were, and the debris could have carried them across the ocean,” Scarpetta speculated.
The Role of Rafts in the Journey
The study suggests that if fallen trees served as rafts, they may have provided food for the iguanas during their long journey across the Pacific. These natural rafts would have been crucial for the survival of the reptiles over such a vast distance.
Brachylophus: An Endangered Outlier
Fiji’s Brachylophus species is not only remarkable for its long-distance journey but is also an outlier among iguana species. Today, it faces severe threats from habitat loss, poaching, and invasive species such as rats.
To better understand the evolutionary history of Brachylophus, Scarpetta conducted a genomic analysis of over 200 iguana specimens, which confirmed the close genetic relationship between Brachylophus and Dipsosaurus. This genetic connection underscores the resilience of desert iguanas, which are known for their ability to withstand harsh conditions, such as dehydration and starvation.
Scarpetta believes that the traits of desert iguanas made them particularly suited to survive the 5,000-mile journey across the Pacific. “If any group of lizards could endure such a long voyage on a mass of vegetation, a desert iguana-like ancestor would be the one,” he explained.
This study not only reshapes our understanding of the evolution of Fiji’s iguanas but also highlights the extraordinary adaptability and resilience of these creatures in the face of nature’s challenges.
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