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Lonesome George the Giant Tortoise’s DNA Reveals Cancer-Fighting and Longevity Genes

The iconic reptile and last Pinta Island tortoise passed in 2012, but a new look at his DNA is helping researchers understand genetics

Lonesome George (Wikimedia Commons)
smithsonian.com

In 2012, Lonesome George—the last Pinta tortoise, or Chelonoidis abingdonii—passed away at the age of 100 in a conservation facility in the Galapagos Islands. While the beloved giant tortoise and his species might be gone, it turns out he’s still got a lot to teach us. Researchers have published George’s genome, which reveals that the tortoises have specialized genes for longevity, immune response and cancer resistance that other vertebrate animals do not possess.

To understand George’s genetics, an international team sequenced the tortoises' DNA as well as the DNA of a less famous but still extant species of giant tortoise Aldabrachelys gigantea found in the Seychelles Islands. The team then compared the tortoise genomes to a wide range of other animals species to see what makes the shelled reptiles special. Their results appear in the journal Nature Ecology & Evolution.

The team found that genes that have been linked to longevity in humans were also found in the tortoises, and that those genes had undergone positive selection, meaning environmental pressures favored tortoises with genes for longer life. They also looked at 891 genes associated with the immune system and found that the reptiles had duplications not found in the human genome. They also discovered tumor-suppressing genes, genes related to DNA repair, and genes that help stave off oxidative stress, which causes some age-related problems.

Sara Chodosh at Popular Science reports that none of the genes on their own are a silver bullet for longevity. But taken together, they can give us some insight into the reasons some animals live fast and die young and others tuck into their shells and live forever.

It also tells us a little bit about giant tortoises. Nature reports in an editorial that in the past, giant tortoise species were found across the Earth. However, over time they died out on the mainland, though pockets of the massive beasts remained on islands with no predators, like the Galapagos. However, when humans began to colonize these places, bringing rats, cats and other nest predators along with them, the turtles saw declines or went extinct. But the new study suggests humans and their pets aren’t the only factor to blame. George’s genome shows that the population of Pinta tortoises had been in decline for the last million years, the natural result of a slow-reproducing species stuck on an island with a limited gene pool.

Even if Lonesome George’s species was already in decline, humans are the main reason for the end of the species. According to the Galapagos Conservancy, the Pinta tortoise was a favorite mid-voyage snack for whalers and seal hunters in the Pacific in the 1800s. By the early part of the 20th century, so many tortoises had been harvested from Pinta island that they were thought to have went extinct. Other than tortoise harvesting, the island remained pretty much untouched—that is until a group of fishermen released three goats on the island, hoping that the little herd would reproduce and provide them fresh meat during their cruises. By 1970, there were 40,000 goats on the island, and they had more or less destroyed the native habitat. In 1971, a researcher spotted a tortoise trying to make a living on the denuded island.

Park rangers brought him in to their tortoise conservation center and determined that he was indeed the last remaining Pinta tortoise, naming him Lonesome George after a comedian. George lived out the rest of his life at the center, reaching 100 though his species can reach 150.

Even though he is gone, George’s DNA lives on. And turtles may once again live on at Pinta Island as well. The goats have been eradicated, and in 2010, 39 sterilized giant tortoises were released onto the island to be “caretakers” of the vegetation until conservationists decide whether they want to move a breeding population of a related species onto the island.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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