Giant tortoise genomes offer insights into longevity

International research into the genome of the late ‘Lonesome George’, the last member of the Galapagos giant tortoise species from Pinta Island, provides extraordinary insights into the species’ large size, as well as its ability to live up to 200 years and fight cancer.

Discovered in 1971 and captured in 1972, Lonesome George lived for almost 40 years under protection at the Tortoise Center on Santa Cruz. For decades, the tortoise didn’t reproduce with females from a similar species on the Galapagos Islands. He died from natural causes in 2012 — but his legacy will live on in more ways than one.

Back in 2010, Yale University’s Adalgisa ‘Gisella’ Caccone began sequencing the whole genome of Lonesome George, in an effort to study the evolution of the tortoise population on the Galapagos. Eight years later, with the assistance of colleagues from Yale as well as the University of Oviedo, Galapagos National Park Service, Flinders University and another nine institutions, the results have been published in the journal Nature Ecology & Evolution.

The researchers additionally sequenced the genome of a giant tortoise from the island of Aldabra in the Seychelles (Aldabrachelys gigantea) and compared both genomes with those of other species — including humans. They paid particular attention to genes thought to be potentially involved in cancer and ageing, directly analysing more than 3000 of them.

“Giant tortoises are amongst the longest living animals and therefore must have evolved mechanisms for reducing their risk of developing cancer,” said study co-author Professor Luciano Beheregaray, from Flinders University.

“Because of that they provide an excellent model to study longevity and age-related diseases.”

The researchers identified several variants in the tortoise genomes that potentially affect six of the nine hallmarks of ageing, with links to DNA repair, immune response and cancer suppression. None of these gene variants are possessed by shorter-lived vertebrates or have been previously associated with the ageing process, so this breakthrough opens fresh research avenues that could lead to an improved understanding of the tortoises’ longevity.

The new genomic data provides important resources to help improve the understanding of giant tortoise biology and to aid efforts to restore giant tortoise populations. The findings also point to evolutionary strategies linked to increased lifespan and age-related diseases, though further studies are needed to determine if these features are indeed associated with suppressing cancer.

Image caption: Lonesome George. Image credit: Galapagos National Park.