Many cold-blooded species hardly age (research)

Being a tortoise, 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, which leads to the death of animals, is inevitable.

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

The researchers “focused more on really thorough comparison work with birds and animals in nature,” says the ecology researcher at 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 comprising 107 populations of 77 wild species, including turtles, amphibians, snakes and crocodilians.

– Senescence –

These studies, by identifying individuals followed over several years, make it possible to estimate, with probabilities, the mortality of a given population.

They also collected data on the animals’ lifespan after sexual maturity and, with statistical methods, determined the rates of aging – or senescence – as well as longevity, that is, 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 study’s lead authors.

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

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

On the other hand, among American women, for example, the risk of dying in the year at age 10 is one in 2,500, against one in 25 at age 80.

– Temperature instead of 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 abuse of language as “cold-blooded” organisms, for an application in humans, they are endothermic.

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

That 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, metabolism rate is not the main factor in senescence.

Other results allow us to trace alternative paths, which still need 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 reverse was true for amphibians.

– Human benefits –

Animals with protective physical attributes, such as shells for turtles or the presence of toxins in certain amphibians, live longer than those without them, the publication adds.

“This allows animals to live longer and evolution to work in a way that reduces aging, so that if they avoid being eaten, they still function well,” explained David Miller.

The second study published 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, both terrestrial and marine, in zoo populations.

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

“If some species actually manage to escape aging, and dedicated studies are able to understand the mechanisms, then human health and longevity could benefit,” write researchers Steven Austad and Caleb Finch in a commentary to their publication.

They note, however, that while some species have a mortality rate that does not increase with age, they accumulate age-related lesions.

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

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