College of Liberal Arts

University of Mississippi

‘Extinct’ Tortoises May Still be Roaming a Galapagos Island

Courtesy of The Los Angeles Times

A giant tortoise species studied by Charles Darwin and believed to be extinct for more than 150 years may be alive and well, an ambitious genetic survey led by Ryan Garrick, assistant professor of biology and population geneticist, has revealed.

Blood sampling of tortoises on the largest Galapagos island of Isabela has shown that some had at least one purebred parent from a supposedly extinct species that once lived at the other end of the archipelago. Garrick and his research team hope to find these tortoises in the flesh, breed them in captivity and then release them back to their native home.

The study, published [in] the journal Current Biology, may be the first rediscovery of an “extinct” species ever made through looking for genetic markers in hybrid offspring.

The giant tortoise, among the largest living reptiles on Earth, is an icon of the Galapagos Islands, which take their very name from the Spanish word for tortoise, galápago. The creatures are thought to have arrived on the volcanic islands about 2 million to 3 million years ago from the South American mainland.

Each tortoise species — some larger, with domed shells, and others smaller, with saddleback shells — was unique to a particular island or volcano, living and evolving in isolation from the others. The diversity of tortoise species Darwin saw during his 1835 visit to the Galapagos Islands partly inspired his theory of evolution.

George Amato, director of the genomics program at the American Museum of Natural History in New York, called the results “very exciting.”

“To be honest with you, I can’t think of another example of this kind of work on endangered species that’s done such a detailed job of reconstructing this very interesting history,” Amato said.

The researchers have some thoughts on how the tortoises managed to get from one of the southernmost islands to the archipelago’s northwestern edge. Fast-moving whalers, or pirates looking to reduce their load while fighting or fleeing, may have hurriedly dumped the animals, taken along for food, at sea.

“These guys don’t swim, but they float like a wine cork in a bathtub,” Garrick said. “The prevailing current goes northwest in the ocean, making [Isabela] island the last place they would catch land before getting swept into the north Pacific.”

The search is now on for live, purebred C. elephantopus tortoises on Isabela. If they’re found, the researchers hope to start a breeding program in captivity to raise more of them and then bring them back to their native island, Floreana.

Tortoises are a very important part of an island’s ecosystem, Garrick said. They keep the prickly pear cactus in check by grazing on it and, by relieving themselves around other parts of the island, also act as the plant’s primary seed-dispersal method.

Even if the purebred tortoises don’t turn up, intensively breeding the most promising hybrids could be useful as well, Garrick added.

“This really comes down to not giving up on biodiversity conservation, even when things look grim,” he said.

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