Mexico’s Spiny Lizard Goes from Invasive Pariah to Protected Species

The Mexican government was all set to eradicate the spiny-tailed iguana on Clarion Island. But now researchers have discovered that the reptile is in fact a native of the remote island and not an invasive species.

Clarion Island is more than 400 miles west of the Mexican mainland and accessible only by boat. The estimated 100 iguanas on the small (less than eight square miles) island share space with a variety of sea birds, including the red-footed booby, heron, and ibis. 

The assumption that the spiny-tailed lizard arrived with humans was disproved by evolutionary biologist Daniel Mulcahy, who visited the island in 2013 to investigate a snake species and happened upon the “invasive” iguanas. The DNA samples he collected which were distinct, genetically speaking, from that of the mainland’s spiny-tailed lizards.

Mulcahy and colleagues determined that the island iguanas had split off from the mainland species around 425,600 years ago, long before humans arrived in the Americas (or anywhere else). The lizards’ ancestors had probably arrived on a floating mat of vegetation, traveling 700 or so miles by sea.

The spiny-tailed iguana (Ctenosaura pectinata) is a big lizard, growing to over four feet long and usually sporting black-and-yellow markings. The Mexican government planned to exterminate them, thinking they were a threat to the island’s delicate ecosystem. Now we know the big guy is a natural part of the island life. Young lizards eat mostly insects but become herbivorous as they age, munching flowers, leaves, and fruit.

“Unlike invasive species, which often require active management, naturally occurring populations such as that of the Clarion Spiny-tailed Iguanas represent an integral component of the island's native biodiversity,” the researchers write in the journal Ecology and Evolution. “Protecting the Ctenosaura population, along with the island's other native reptile species, should be a priority in conservation planning.”

Photo credit: Jacobo Reyes-Velasco / Ecology and Evolution