Wild turtles age slowly, and some species “do not age”; to understand

Recently, Jonathan the Seychellois giant tortoise (Aldabrachelys gigantea hololissa) made headlines as the oldest living land animal at 190 years old.

Jonathan, the Seychellois giant tortoise (Aldabrachelys gigantea hololissa), is the world’s oldest land animal at 190 years old. Image: Luke McKernan – Creative Commons

While there is similar evidence that some species of tortoises and other ectothermic – or “cold-blooded” – animals live long lives, the evidence is mostly about animals that live in zoos or a few individuals in the wild.

A team of researchers conducted the most comprehensive study of aging and lifespan to date, including data collected in the wild from 107 populations of 77 reptile and amphibian species worldwide. The results were published in the journal The science last Thursday (23).

What is “absence of biological aging”?

Among the published results, researchers have documented for the first time that turtles, crocodiles and salamanders have particularly low rates of aging and extended lifespans for their size. The team also found that protective phenotypes, such as the hard shell of most turtle species, contribute to slower maturation and, in some cases, even “negligible aging” – or no biological aging.

“There is anecdotal evidence that some reptiles and amphibians age slowly and have longer lifespans, but so far no one has studied this on a large scale in many species in the wild,” said David Miller, study lead author and associate professor. Ecology of Wildlife Populations at Pennsylvania State University, USA. “If we can understand what makes certain animals age more slowly, we can better understand aging in humans, and we can also develop conservation strategies for reptiles and amphibians, many of which are endangered or endangered. »

1656347228 428 Wild turtles age slowly - and some species
The defense phenotype hypothesis suggests that animals with physical or chemical characteristics that provide protection, such as tortoiseshell, age more slowly and have longer lifespans. Image: Photography by Kim Lewis –

In their study, the researchers applied comparative phylogenetic methods that study the evolution of organisms to tagging data where animals are captured, tagged, released into the wild, and observed.

The aim of the scientists was to analyze the differences in aging and lifespan of exotherms in nature compared to endotherms (warm-blooded animals) and explore previous hypotheses related to aging, including body temperature regulation and the presence or absence of protective physical traits.

Miller explains that the “thermoregulatory regime hypothesis” suggests that exotherms age more slowly than endotherms, which internally generate their own heat and have a higher metabolism. Indeed, cold-blooded animals need outside temperature to regulate their body temperature, and therefore often have lower metabolisms.

“People tend to think, for example, that mice age quickly because they have a high metabolism, and turtles age slowly because they have a low metabolism,” he explained.

Turtles are unique animals

However, the new approach shows that how an animal regulates its temperature – cold-blooded or warm-blooded – is not necessarily indicative of its rate of aging or lifespan.

“We didn’t find support for the idea that a lower metabolic rate indicates that exotherms age more slowly,” says Miller. “This association was only true for tortoises, suggesting that tortoises are unique among cold-blooded animals. »

The defensive phenotype hypothesis suggests that animals with physical or chemical traits that provide protection, such as armor, spikes, hooves, shells, or poison, age more slowly and live longer.

As documented by the team, these protective traits actually allow animals to age more slowly and, in the case of physical protection, live much longer for their size than animals without protective phenotypes.

“Perhaps their altered, stiff-hoofed morphology provided protection and contributed to the evolution of their life histories, including little or no aging and exceptional longevity,” explained Ann Bronicowski, co-author and professor of integrative sciences. biology at Michigan State University.

“These various defense mechanisms can reduce animal mortality because they are not eaten by other animals,” said Beth Reinke, first author and assistant professor of biology at Northeastern Illinois University. “Therefore, they are more likely to live longer, leading to slower aging. We found the strongest support for the defensive phenotype hypothesis in turtles. This demonstrates that turtles as a group are unique. »

The team observed slight aging in at least one species in each of the exothermic groups, including toads and frogs, crocodiles and turtles. “It sounds dramatic if they don’t age, but basically the likelihood of them dying doesn’t change with age when they go beyond reproduction,” Reinke explained.

According to Miller, negligible aging indicates that if the risk of an animal dying within one year is 1% at 10 years old, the risk of an animal dying at 100 years old is still 1%. “In contrast, among adult women in the United States, the risk of dying within a year is about 1 in 2,500 at age 10 and 1 in 24 at age 80. When a species has little aging (decay), aging simply does not occur.

Reinke notes that the team’s new study was only made possible by the contributions of a large number of collaborators around the world studying a wide variety of species. “Being able to pull together the information that all researchers have collected over years of studying individual species has allowed us to get these more reliable estimates of aging rates and lifespans based on demographics rather than individual animals. . »

Bronicowski adds that “understanding the comparative landscape of aging in animals may reveal flexible traits that could be valid targets for biomedical research related to human aging.”

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