194-year-old Aldabra tortoise Jonathan studied for longevity secrets
Scientists studying the world's oldest-known land animal, a 194-year-old Aldabra giant tortoise named Jonathan, have identified genetic traits and epigenetic markers that may explain his extraordinary lifespan. The research, published in Science Advances, found unique variants in genes linked to tum
Scientists have published a study into the world's oldest-known terrestrial animal, an Aldabra giant tortoise named Jonathan, to explore the secrets of his remarkable longevity. Estimated to be about 194 years old and resident at the governor's residence on the remote South Atlantic island of St Helena, Jonathan has far exceeded the species' typical lifespan of more than 100 years. The study, published on Wednesday in the journal Science Advances, sequenced his genome and analysed his epigenome — the chemical markers that control which genes are switched on or off.
"We found changes in Jonathan's genome in pathways associated with longevity, like DNA repair, mitochondrial function, insulin regulation and telomere function," said Benjamin Vaisvil, a researcher affiliated with the organisation Kallel and co-lead author of the study. The researchers identified 287 genes with variants unique to Jonathan, including some linked to tumour suppression and DNA repair. The tortoise also carries extra copies of a gene that encodes a protein that hunts down ageing and cancerous cells.
To explain the epigenetic findings, Vaisvil compared the genome to a cookbook and the epigenome to handwritten notes in the margins. "As the cookbook ages, those notes become more difficult to read clearly. We can think of that as methylation entropy," he said, referring to a metric for disorder in a certain biochemical process. Most of the notes in Jonathan's "cookbook" look very old. However, in certain stretches of DNA that act as switches controlling gene activation, Jonathan's methylation entropy was lower than that of every tortoise studied except a 5-year-old juvenile. These regions controlled genes that influence longevity.
Researchers compared Jonathan's epigenome with four other Aldabra tortoises, ranging from juveniles to older adults. Samples were obtained by scraping under Jonathan's tongue with a specialised kit while he was distracted by feeding. St Helena officials restrict blood draws to prevent infection risks. The study involved only one exceptionally old tortoise, making it difficult to determine whether the traits identified are unique to Jonathan or common among long-lived tortoises. "We cannot say for certain that what we found is the reason for his longevity," Vaisvil said.
The research findings broadly match patterns documented in studies of exceptionally long-lived people, suggesting that some mechanisms of ageing may be shared across species. Vaisvil noted that a recent study of a 117-year-old woman found unusually efficient mitochondrial function, echoing findings in some of Jonathan's regions. Environmental factors also may have contributed; Jonathan lives on a tropical island with an optimal diet carefully managed by trained veterinarians.
Brought to St Helena as a fully grown animal in 1882, likely from the Aldabra Atoll or the Granitic Seychelles, Jonathan has lived through world wars and the rise and fall of empires. "He is symbolic of resilience, longevity, endurance, a persistent presence throughout huge historic events," said Joe Hollins, the tortoise's longtime veterinarian and study co-author. Despite cataracts that have left him mostly blind, Jonathan retains a voracious appetite and is described by Hollins as "a gentle giant." Guinness World Records has granted him "icon" status this year.
