To be a turtle, the secret behind eternal youth? The low aging observed in cold-blooded species, according to two studies published on Thursday, questions the idea that progressive biological degradation, leading to animal death, is inevitable.
In addition to a few specific cases – such as the 190-year-old “Jonathan” turtle – the issue had not been investigated so thoroughly, David Miller, co-author of one of the two articles, told AFP. published in the prestigious journal “Science”.
Researchers “had focused more on a truly complete comparison work with birds and animals in the wild,” says the ecology researcher from Penn State University in the United States. “But what we knew about amphibians and reptiles came from one species here, another there …”
For his work, David Miller collected long-term fieldwork data covering 107 populations of 77 animal species, including turtles, amphibians, snakes, and crocodiles.
– Old age –
These studies, by identifying and subsequently following individuals over several years, make it possible to estimate with probability the mortality of the given population.
They also collected data on the life of the animals after sexual maturity and determined by statistical methods the rate of aging – or old age – as well as life expectancy, ie here the age at which 95% of the population is already dead.
“We found examples of minimal aging,” continued Beth Reinke, a biologist at Northeastern University in the United States and one of the lead authors of the study.
While expecting this for turtles, similar findings emerged for a species in each group of cold-blooded animals, including frogs and crocodiles.
“Minimal aging or old age does not mean that they are immortal,” the researcher clarified: they have a chance of dying, but this probability does not increase with age.
Conversely, among American women, for example, the risk of dying each year at age 10 is one in 2,500, versus one in 25 at age 80.
– Temperature rather than metabolism –
The study was funded by the American Institutes of Health (NIH), which seeks to better understand the aging of ectothermic organisms, often identified by language abuse as “cold-blooded” organisms, for use in humans, those endotherms.
Researchers have long believed that ectotherms age less rapidly because of their dependence on the environment to regulate their temperature, which slows down their metabolism, as opposed to endotherms that produce their own heat and have a higher metabolism.
This compound remains true for mammals: mice have a faster metabolism than humans and a shorter life expectancy.
However, according to this new study, and contrary to what we previously thought, the rate of metabolism is not the primary factor in old age.
Other results make it possible to draw alternative paths that need to be explored.
By looking at the average temperature of a species, not its metabolism, the authors found that the warmest reptile species age faster than others, while the reverse was the case for amphibians.
– Human benefits –
Animals with physical protective properties, such as turtle shells or the presence of toxins on certain toads, live longer than those without them, the publication adds.
“It allows animals to live longer, and evolution can work in a way that reduces aging, so if they avoid being eaten, they still work well,” David Miller explained.
The second study published on Thursday, led by a team from the University of Southern Denmark and other laboratories, presents the results of a similar method applied to 52 species of turtles, land and sea, in zoos.
Of these species, 75% showed minimal aging, the researchers concluded.
“If some species really manage to escape aging, and dedicated studies manage to understand the mechanisms, human health and longevity could benefit,” researchers Steven Austad and Caleb Finch write in a commentary on their publication.
However, they note that while some species have a mortality rate that does not increase with age, they accumulate age-related damage.
Jonathan, the 190-year-old turtle, “is now blind, has lost his sense of smell and needs to be hand-fed,” the researchers say.