Source : Perth Now news
The world’s oldest-known terrestrial animal, an Aldabra giant tortoise named Jonathan and estimated to be about 194 years old, might owe his extraordinary longevity to a combination of genetic traits and an ability to keep key cellular systems functioning in a more youthful way, scientists say.
Members of this species are known to live more than 100 years, but Jonathan has far exceeded that.
Brought to the remote South Atlantic island of St Helena as a fully grown animal in 1882, likely from the Aldabra Atoll or the Granitic Seychelles, the tortoise now resides in a paddock at the governor’s residence.
“Other Aldabra tortoises have been claimed to have lived as long as Jonathan, but he has the most documentary evidence supporting his age,” said Benjamin Vaisvil, a researcher affiliated with the organisation Kallel and co-lead author of the study published on Wednesday in the journal Science Advances.
Scientists have studied Jonathan to explore the secrets of the animal’s amazing longevity, sequencing his genome and analysing his epigenome – the chemical markers that control which genes switch on and off.
“We found changes in Jonathan’s genome in pathways associated with longevity, like DNA repair, mitochondrial function, insulin regulation and telomere function,” Vaisvil said.
Researchers compared Jonathan’s epigenome with four other Aldabra tortoises, ranging from juveniles to older adults.
To explain the 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,” Vaisvil said, referring to a metric for disorder in a certain biochemical process.
Most of the notes in Jonathan’s “cookbook” look very old.
But in certain regions, stretches of DNA that act as switches controlling whether genes are turned on or off, Jonathan’s methylation entropy was lower than that of every tortoise studied except a five-year-old juvenile.
These regions controlled genes that influence longevity.
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.
Determining how long giant tortoises can live is challenging because reliable historical records are scarce and many outlive researchers.
While a young tortoise’s age can be estimated from growth rings on the plates that form the animal’s shell, ascertaining the age of adults is more difficult.
The new study involved only one exceptionally old tortoise, making it hard to determine whether the traits identified are unique to Jonathan or common among long-lived tortoises.
Environmental factors also might have contributed.
Jonathan lives on a tropical island, with an optimal diet carefully managed by trained veterinarians.
The research findings broadly match patterns documented in studies of exceptionally long-lived people, suggesting that some mechanisms of ageing might be shared across species.
