After the discovery of the Galapagos Islands in 1535, the sailors began to hunt live giant tortoises as a source of non-perishable food. Three centuries later, the annihilation of these animals was patent. Charles Darwin then studied the different shells of these turtles during the voyage of Beagle, which helped him formulate the theory of evolution. George the Solitaire, a giant turtle male from Pinta Island, was found in the early 70s of the last century and moved to a wildlife sanctuary. In 2012 he appeared dead in his corral. He died without offspring due to lack of females at an age that could be around 100 years. He was the last of his kind.
An international team of scientists has managed to sequence the complete genome of the animal from blood samples taken in 2010. The results, published today in Nature Ecology and Evolution, open a valuable chest of genetic data that can explain why certain animals manage to reach very advanced ages without suffering diseases such as cancer.
It is believed that tumors are very rare in turtles, highlights the work. The genome of this animal has 27,200 genes, significantly more than a human, with about 22,000. "We have analyzed 500 genes in search of those that play a role in The nine known aging factors", Explains Víctor Quesada, biochemist at the University of Oviedo and first author of the study. "Among all of them we have detected 12 genes that contribute to six of these factors, so from now on they become especially interesting in research," he says.
The results reveal interesting connections between especially long-lived species that, however, are separated by millions of years of evolution. For example, the genome of George the Solitary shows a possible prominent role of the FGF19 gene, the same one that also seems key in humans who have lived 100 years or more.
The ancestors of the giant tortoises of Galapagos (Ecuador) came to the islands from continental America about three million years ago. Compared to mammals, George's species (Chelonoidis abingdonii) developed additional copies of genes related to the immune system, including those that enhance the production of T lymphocytes responsible for eliminating pathogens and cancer cells, the study highlights. The turtle's genome also shows that other genes lost their ability to synthesize proteins. Among them is the NLN, whose deactivation in mice increases glucose absorption and insulin sensitivity, a protection against diabetes, another of the most important ailments associated with age. Compared with other vertebrates, the C. abingdonii It has also developed more copies of several genes that could protect against the appearance of tumors.
The giant turtle also seems to have reinforced the natural mechanisms of DNA repair, whose wear over time is a well-known marker of aging. These chelonians have developed additional copies of genes related to the NEIL1 protein, which has been found in higher amounts in two other species: humans and the amazing bald mole rat, the longest-living rodent and one of the most resistant mammals to cancer.
"The giant tortoises of the Galápagos are an excellent example of evolution of longevity due to the unique conditions and the lack of predators", highlights João Pedro de Magalhães, researcher at the University of Liverpool and expert in the analysis of the genome of extraordinarily long-lived mammals like the Greenland whale, who lives 200 years. "It is not a surprise that this study unveils genetic routes similar to those we found in our studies but with different genes, because we believe that each species uses different tricks to live for many years, and therefore we have to learn how many more", highlights . At the moment this type of studies provide fundamental knowledge about the different adaptations in very diverse species to achieve greater longevity, but in the future they could have a positive impact for people, says De Magalhães. "If we discover genetic adaptations that increase the longevity and resistance to cancer in these animals, it could be viable to transfer them to humans, for example with drugs that mimic the effects of these mutations or by applying gene therapy," the researcher ventures.
The genome of this turtle shows a prominent role of the FGF19 gene, the same one that also seems key in humans who have lived 100 years or more
Although George's species has become extinct, part of its genome still lives on hybrid specimens, a mix of turtles from different islands within the Galápagos archipelago. The guilt of these crossings is again that of the sailors, who collected turtles from an island and threw them overboard in close proximity to others when they no longer needed them. The team of Adalgisa Caccone, a researcher at Yale University and co-author of the study, is trying to recover the extinct turtles of Floreana Island by crossing hybrids found on other islands. "Regarding the species of George, for now we are looking for individuals that descend from these crosses that we have found on Isabela Island. If we find enough we can start a new breeding program, "he explains.