Dr Joe Hollins slides a thick welding glove onto his left hand and grips a cotton swab tightly in his right. He squats down to eye level with a 400-pound giant tortoise, cradles its head with his gloved hand and carefully wedges a finger into its mouth to prop open its razor-sharp beak. With his other hand, he tries to swab its cheek.
Hollins, a veterinarian, has only about five seconds to get the DNA he’s after before he risks getting punched with a thick, scaly leg.
The first swab comes back covered in half-chewed carrot — a favourite snack. He tosses it aside and tries again. The tortoise, named Jonathan, looks mildly annoyed.
At about 194 years old, Jonathan is the world’s oldest known land animal. He’s an Aldabra giant tortoise living 1,200 miles off Africa’s west coast on the remote island of St. Helena, spending his days on the sun-dappled grounds of the official home of the governor. (At the time of his arrival on St. Helena, he was at least 50 years old, a determination his keepers made based on size.)
Although he shows some signs of ageing, like cataracts that have left him mostly blind, he still has excellent hearing and a strong libido. He enjoys greeting visitors, having his neck petted and delivering loud belches for the crowd that gathers around his paddock during mealtimes.
In June, after Jonathan was erroneously declared dead by some media organisations, the Guinness World Records added him to its list of global icons, honouring his superlative status. And Wednesday, he reached another milestone when a study announced that his genome had been sequenced for the first time.
“We almost never get to study an animal this old while it is still alive,” said Steve Horvath, a biologist who studies ageing at UCLA and an author of the study, which was published in the journal Science Advances.
Jonathan gave scientists the rare opportunity to study what happens to an animal’s genome over the course of nearly 200 years. But obtaining the DNA wasn’t easy: The researchers were not permitted to take a blood sample, the gold standard in DNA sequencing, because of the risk of infection.
The researchers were committed to the idea, though, because they were curious if Jonathan’s DNA held secrets about ageing or longevity. Just think: When this tortoise was presumably born in 1832, Charles Darwin was only 22 years old and hadn’t yet visited the Galápagos Islands, where he would dream up his theory of natural selection.
After sequencing the sample, the scientists compared Jonathan’s genome with those of tortoises 100 years his junior and found some molecular differences, especially in genes involved with DNA repair and the maintenance of the protective caps on chromosomes, called telomeres. The results hint that this species may have evolved to be more resilient to age-related decline, but further testing is needed.
The team also discovered that Jonathan shared some genes with other long-living species like naked mole rats, which can live to 40 and rarely get cancer.