Turtles, champions in longevity: a study reveals that they barely age

At 190 years old, Jonathan the tortoise is officially the oldest known living land animal on the planet.

The estimation of its age has been possible thanks to the fact that this giant tortoise from Seychelles, whose date of birth has been established in 1832, lives in the official residence of the Governor of the island of Saint Helena.

In diplomatic relations between countries, the exchange of animals as a gift and symbol of friendship was common, and Jonathan, who was already half a century old when he was transferred to his current residence, The Plantation House, has seen some thirty governors pass through it .

Jonathan's longevity is impressive but not exceptional, because with more or less evidence, other cases of centennial tortoises are known that suggest that for them, the years do pass in vain.

The slowness with which they age is one of the most intriguing aspects of biology, an evolutionary advantage whose mechanisms an international team is trying to clarify this week in two studies published in the journal

in which more than a hundred scientists have participated.

This is the most ambitious research carried out to date to understand the aging process of these animals, work that has shown that

, that is, the gradual process of deterioration of an organism with age.

A capacity, that of stopping aging, which is exceptional in turtles.

Behind the desire to know what this ability is due to so that the years do not make a dent in the turtles, there is an interest in extrapolating what has been learned to human aging, as recognized by David Miller, co-author of one of the studies and associate professor of Ecology at Penn State University: "

and also establish conservation strategies for reptiles and amphibians, many of which are threatened or endangered ".

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In the first of the two studies, 107 populations of 77 species of reptiles and amphibians in zoos around the world were analyzed, which made it possible to document for the first time that turtles, crocodiles or salamanders age more slowly and have hopes of life higher than would be expected for the size of their bodies.

"There was anecdotal evidence that some reptiles and amphibians age slowly and have long lifespans, but until now no one had studied this on a large scale across numerous species," says Miller.

The authors compared species of ectothermic or cold-blooded animals (i.e., those whose body temperature varies with environmental temperature) such as turtles, with endotherms (warm-blooded, such as dogs and humans) to test previous hypotheses about aging, among them, to what extent the presence or absence of protective physical features such as shells influences, and if it has to do with the way in which a living being regulates its body temperature.

One of their conclusions was that the characteristic hard shells that most species of turtles have help to slow down their aging and even in some cases practically stop it, as the authors of this research have shown.

They also saw how

and in the case of physical protection, to live much longer for their size than those that do not have them.

As Beth Reinke, first author of one of the two studies and a professor at Northeastern Illinois University, explains, various protective mechanisms can reduce animal mortality rates because other animals don't eat them: "So it's more likely to live longer, and that puts pressure to age more slowly."

This protective mechanism hypothesis, she adds, is especially applicable to the turtle, in which their

also identified as an antiaging factor .

A frog from San Antón ('Hyla molleri')Iñigo Martínez-Solano

Much has also been said about temperature regulation.

According to Miller, this hypothesis suggests that because they require external temperatures to regulate their body temperature and thus often have lower metabolisms, cold-blooded animals age more slowly than warm-blooded animals (which internally generate their own heat and have higher metabolisms).

"People tend to think, for example, that mice age fast because they have a high metabolism, while turtles age slowly because they have a low metabolism," Miller said.

However, their findings revealed that the aging rates and lifespans of ectotherms vary widely, suggesting that how an animal regulates its temperature (cold-blooded versus warm-blooded) is not necessarily indicative of its rate of growth. aging or life expectancy.

Thus, the longevity of ectotherms ranged from 1 to 137 years.

For comparison, that of primates ranges from 4 to 84 years.

"We found no support for the idea that a lower metabolic rate means that ectotherms age more slowly," says Miller.

"That relationship was only true for turtles, suggesting that they are unique among ectotherms."

The team observed "negligible aging" in at least one species in each of the ectothermic animal groups, including frogs and toads, crocodiles and turtles.

"It sounds dramatic to say that they don't age at all, but basically

says Reinke.

They also found little evidence of aging in some salamanders and in the tuatara, a reptile.

A common tuatara ('Sphenodon punctatus')Sarah Lamar

In the second study, led by Rita da Silva from the University of Southern Denmark, they focused on analyzing 52 species of terrestrial and aquatic turtles.

In 75%, senescence was slow or negligible and 80% experienced lower aging rates than modern humans.

"Negligible aging means that if the probability of an animal dying in a year is 1% when it is 10 years old, if it is alive at 100 years, the probability of dying is still 1%. By contrast, in For adult females in the United States, the risk of dying in a year is approximately 1 in 2,500 by age 10, and 1 in 24 by age 80. When a species exhibits negligible senescence (deterioration), aging it just doesn't happen," says Miller.

However, the fact that some of these animals practically do not age, explains Fernando Colchero, professor at the University of Southern Denmark and co-author, only means that their risk of death does not increase as they age.

Everyone will end up dying from disease or some other cause.

Another conclusion of this work is that some species of tortoises age less when they enjoy better environmental conditions, to a greater extent than humans.

And it is as Da Silva assures, "senescence is not inevitable for all organisms".

THE IMPORTANCE OF TELOMERES

Telomeres play an important key in the aging of many species, as was shown in 2019 by a team from the National Cancer Research Center (CNIO) led by María Blasco after comparing the senescence of people with that of eight other animal species with different expectations of survival. life: the Sumatran elephant, the mouse, the goat, the bottlenose dolphin, the reindeer, the griffon vulture, the red flamingo and the Audouin's gull.

The longevity of a living being, they maintain, depends on its telomeres, which are the structures that protect the chromosomes.

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