The tide may be turning for the rare species of giant tortoise thought to have gone extinct when its last known member, the beloved Lonesome George, died in June.
This isn't the first time Chelonoidis abingdoni has been revived: The massive reptiles were last seen in 1906 and considered extinct until the 1972 discovery of Lonesome George, then around 60 years old, on Pinta Island. The population had been wiped out by human settlers, who overharvested the tortoises for meat and introduced goats and pigs that destroyed the tortoises' habitat and much of the island's vegetation.
Now, in an area known as Volcano Wolf—on the secluded northern tip of Isabela, another Galápagos island—the researchers have identified 17 hybrid descendants of C. abingdoni within a population of 1,667 tortoises.
Genetic testing identified three males, nine females, and five juveniles (under the age of 20) with DNA from C. abingdoni. The presence of juveniles suggests that purebred specimens may exist on the island too, the researchers said.
"Even the parents of some of the older individuals may still be alive today, given that tortoises live for so long and that we detected high levels of ancestry in a few of these hybrids," Yale evolutionary biologist Danielle Edwards said.
How did Lonesome George's relatives end up some 30 miles (50 kilometers) from Pinta Island? Edwards said ocean currents, which would have carried the tortoises to other areas, had nothing to do with it. Instead, she thinks humans likely transported the animals.
Crews on 19th-century whaling and naval vessels hunted accessible islands like Pinta for oil and meat, carrying live tortoises back to their ships.
Tortoises can survive up to 12 months without food or water because of their slow metabolisms, making the creatures a useful source of meat to stave off scurvy on long sea voyages. But during naval conflicts, the giant tortoises—which weighed between 200 and 600 pounds (90 and 270 kilograms) each—were often thrown overboard to lighten the ship's load.
That could also explain why one of the Volcano Wolf tortoises contains DNA from the tortoise species Chelonoidis elephantopus, which is native to another island, as a previous study revealed. That species is also extinct in its native habitat, Floreana Island.
(Related: "No Lovin' for Lonesome George.")
Life After Extinction?
Giant tortoises are essential to the Galápagos Island ecosystem, Edwards said. They scatter soil and seeds, and their eating habits help maintain the population balance of woody vegetation and cacti. Now, scientists have another chance to save C. abingdoni and C. elephantopus.
With a grant from the National Geographic Society's Committee for Research and Exploration, which also helped fund the current study, the researchers plan to return to Volcano Wolf's rugged countryside to collect hybrid tortoises—and purebreds, if the team can find them—and begin a captive-breeding program. (National Geographic News is part of the Society.)
If all goes well, both C. abingdoni and C. elephantopus may someday be restored to their wild homes in the Galápagos. (Learn more about the effort to revive the Floreana Galápagos tortoises.)
"The word 'extinction' signifies the point of no return," senior research scientist Adalgisa Caccone wrote in the team's grant proposal. "Yet new technology can sometimes provide hope in challenging the irrevocable nature of this concept."
The new Lonesome George study was published by the journal Biological Conservation.