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Many cold-blooded species barely get old

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Being a turtle, the secret of eternal youth? The low aging observed in cold-blooded species calls into question, according to two studies published Thursday, the idea that progressive biological degradation, leading to the death of animals, is inevitable.

Beyond a few specific cases – such as the 190-year-old “Jonathan” tortoise – the matter has not been studied as thoroughly, David Miller, co-author of one of the two articles, told AFP. “Science” magazine.

The researchers “focused more on really comprehensive 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 field data comprising 107 populations of 77 wildlife species, including turtles, amphibians, snakes and crocodiles.

These studies, then identifying following individuals over several years, allow us to estimate, with probability, the mortality of a given population.

They also collected data on the lifespan of the animals after sexual maturity and, using statistical methods, determined the rates of aging – or senescence – as well as longevity, i.e. the age at which 95% of the population is already. died.

“We found examples of minimal aging,” continued Beth Reinke, a biologist at Northeastern University in the United States and one of the study’s lead authors.

While this was expected for turtles, similar findings emerged for one species in every group of cold-blooded animals, including frogs and crocodiles.

“Minimal aging or senescence does not mean that they are immortal,” explained the researcher: they have the possibility of dying, but this probability does not increase with age.

In contrast, among American women, for example, the risk of dying within a year at the age of 10 is one in 2,500, compared to one in 25 at the age of 80.

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 human application. their endothermic.

Scientists have long believed that ectotherms age less rapidly due to their reliance on the environment to regulate their temperature, which lowers their metabolism, unlike endotherms, which produce their own heat and have a higher metabolism.

This link remains true for mammals: mice have a faster metabolism than humans and a shorter life expectancy.

But according to this new study, and contrary to what we previously thought, the rate of metabolism is not the main factor in senescence.

Other results make it possible to trace alternative routes, which remain to be studied.

By looking at a species’ average temperature, not its metabolism, the authors found that warmer reptile species aged faster than others, while the opposite was true for amphibians.

Animals with physical protective attributes, such as turtle shells or the presence of toxins on some amphibians, live longer than those without them, the publication adds.

“It allows animals to live longer and evolution to work in ways that reduce aging so that if they avoid being eaten, they still function well,” explained David Miller.

The second study released Thursday, led by a team from the University of Southern Denmark and other labs, presents the results of a similar method applied to 52 species of turtles, terrestrial and marine, in zoo populations.

Of these species, 75% showed minimal aging, the scientists concluded.

“If some species actually manage to escape aging and dedicated studies can understand the mechanisms, the health and longevity of humans could benefit,” write researchers Steven Austad and Caleb Finch in a comment to their publication.

They note, however, that while some species have mortality rates that do not increase with age, they accumulate age-related injuries.

Jonathan, the 190-year-old tortoise, “is now blind, has lost his sense of smell and needs to be fed manually,” say the scientists.

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