A spiny-tailed iguana, once considered an unwelcome visitor to a remote Mexican island, has been proven to be a long-time resident—a surprising finding that rewrites the island’s natural history. After decades of speculation, biologists have confirmed the iguana’s ancestors arrived on Clarion Island in the Pacific Ocean nearly half a million years ago, predating any human influence.
A Remote Archipelago and a Lizard Mystery
Clarion Island is part of the Revillagigedo Islands, a sparsely populated Mexican archipelago located far out in the Pacific Ocean. For years, the approximately 100 iguanas inhabiting Clarion Island were thought to be an invasive species, likely introduced by humans in the late 20th century. This assumption arose because earlier documentation of the island’s wildlife made no mention of these lizards. This narrative reflects a common challenge in ecological studies: limited historical data can lead to incorrect assumptions about a species’ origin.
Challenging Long-Held Assumptions
“It was all speculative that they were introduced—no one ever tested it,” explained Daniel Mulcahy, an evolutionary biologist at the Museum of Natural History in Berlin and a co-author of a recent study published in the journal Ecology and Evolution.
The breakthrough came unexpectedly. In 2013, Dr. Mulcahy visited Clarion Island while investigating rumors of a snake species. While on the island, he observed the iguanas and collected DNA samples. Initial analysis revealed a key difference: the iguanas’ genetic makeup did not align with that of mainland spiny-tailed iguanas.
Ancient Origins Revealed Through DNA
The Genetic Evidence
The team compared the Clarion Island iguana’s DNA with that of iguanas from across Mexico and Central America. The genetic data strongly suggested a separation from the mainland population over 500,000 years ago. This finding indicates that the island’s iguanas are descendants of a lineage that inhabited the region long before humans began traveling extensively in the area.
How Did They Arrive?
The exact mechanism by which the iguanas reached Clarion Island remains a topic of ongoing research, but scientists theorize that they may have been swept away by powerful ocean currents. The Revillagigedo Islands were formed by volcanic activity and were once part of a larger landmass. Changes in sea levels and tectonic shifts likely created geographic barriers, isolating the iguana population on Clarion Island.
Implications for Conservation
The discovery has significant implications for conservation efforts. Recognizing the iguanas as native inhabitants means that they are no longer considered an invasive species, and their protection is now a priority. This finding highlights the importance of genetic research in understanding the history of island ecosystems and making informed conservation decisions.
This discovery underscores the remarkable resilience of life and the unexpected ways species can adapt and thrive over immense stretches of time.
The iguana’s story provides a fascinating glimpse into the deep evolutionary history of the Pacific Ocean and demonstrates how genetic research can rewrite our understanding of the natural world. It serves as a reminder that what we once believed to be invaders may, in fact, be ancient residents, playing a vital role in the island’s ecosystem
