Genome of Jonathan, 194-year-old tortoise, hints at how he has lived so long

Mixed · 2Scientists have analysed the genome of Jonathan, an Aldabra giant tortoise on St Helena in the South Atlantic who is believed to be about 194 years old and is described as the world's oldest known living land animal. 1 2 Mixed · 2The study was published on Wednesday in the journal Science Advances, with Benjamin Vaisvil as co-lead author; researchers are affiliated with the non-profit Kallel Foundation, including Stephen Clark. 2 1 Mixed · 2Jonathan was brought to St Helena in 1882 as a fully grown adult, thought to be about 50 years old already, which gives the estimate of 194; he lives in the grounds of Plantation House, the governor's residence. 3 1

Centre · 2Vaisvil said other Aldabra tortoises have been claimed to live as long, but Jonathan has the most documentary evidence for his age; New Scientist says the researchers calculated an average Aldabra lifespan of around 80 years. 2 3 Centre · 2The team sequenced his genome and analysed his epigenome, the chemical markers controlling which genes switch on and off, comparing it with four other Aldabra tortoises ranging from juveniles to older adults. 3 2 Centre · 2They found 287 genes with variants unique to Jonathan, including some linked to tumour suppression and DNA repair; New Scientist adds that 41 are thought functionally significant and a dozen also appear in ageing databases of other long-lived animals. 2 3

Centre · 1Vaisvil said changes were found in longevity-associated pathways including DNA repair, mitochondrial function, insulin regulation and telomere function, and CNA reports extra copies of a gene encoding a protein that hunts down ageing and cancerous cells. 2 Mixed · 2The most striking result concerned mitochondria, the cell's power structures: methylation patterns on mitochondria-related genes matched those of much younger animals, with methylation entropy lower than in every tortoise studied except a 5-year-old. 1 2 Centre · 2Clark suggested efficient mitochondria may give DNA repair systems more energy to counter ageing, and said some of Jonathan's genetic changes resemble those of human supercentenarians; the work echoes a study of a 117-year-old woman that found unusually efficient mitochondrial function. 3 2

Centre · 1The researchers had to work with saliva and cheek samples because St Helena authorities restrict blood draws over infection risk, which New Scientist says limited the quality of the genome and required gaps to be filled using DNA from another tortoise. 3 Mixed · 2The authors caution against firm conclusions: the Guardian says it is unclear whether or how much the patterning contributes to his lifespan, and Vaisvil said "We cannot say for certain that what we found is the reason for his longevity". 1 2 Centre · 2Only one very old tortoise was studied, so traits may be unique to him or common in long-lived tortoises; Kousuke Hashimoto of the University of Osaka called the work fascinating but noted the small comparison group, and CNA notes his tropical island home and carefully managed diet may also matter. 3 2

Left · 1Clark said next steps include validating the finding, for instance by testing whether mitochondria can be made young or replaced to extend longevity. 1 Mixed · 2Jonathan's care has been led by vet Joe Hollins (spelt Hollis in the Guardian), who began hand-feeding him in 2009 when he was blind, had lost his sense of smell and had a soft beak; he is now described as a gentle giant who still has a voracious appetite and recently mated with another tortoise, Emma. 1 2 Left · 1In April a fake X account posing as the vet claimed Jonathan had died in a crypto scam; St Helena's governor, Nigel Phillips, found him asleep and 'very much alive'. 1