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Studies show that many cold-blooded creatures do not age – Science-Environment News – Report by AFR

Scientists have discovered the secret of eternal youth: being born a turtle.

Two studies published Thursday in the journal Science revealed scant signs of aging in certain cold-blooded species, challenging an evolutionary theory that says senescence, or gradual physical deterioration over time, is an inevitable fate.

Although there have been striking anecdotal reports — such as that of Jonathan, the Seychelles tortoise, which turns 190 this year — these have been considered anecdotal and the topic has not been systematically investigated, said Penn State wildlife ecologist David Miller, a senior Author of one of the newspapers, told AFP.

Researchers have done “a lot more comparative, really broader work with birds and animals in the wild,” he said, “but a lot of what we knew about amphibians and reptiles came from a species here, a species there.”

For their work, Miller and colleagues collected data from long-term field studies involving 107 populations of 77 species in the wild, including turtles, amphibians, snakes, crocodiles and tortoises.

These all used a technique called ‘mark-recapture’, in which a certain number of individuals are captured and marked, and researchers then follow them over the years to see if they can find them again and derive mortality estimates based on probabilities.

They also collected data on how many years the animals lived after they reached sexual maturity and used statistical methods to estimate rates of aging and longevity — the age at which 95 percent of the population is dead.

“We found examples of negligible aging,” said biologist and principal investigator Beth Reinke of Northeastern Illinois University.

Although they expected this to be true of turtles, it has also been found in one species from each of the cold-blooded groups, including frogs, toads and crocodiles.

“Negligible aging or senescence does not mean they are immortal,” she added. It means there is a chance of dying, but it doesn’t increase with age.

In contrast, the risk of dying within a year for US adult women at age 10 is about one in 2,500, compared to one in 24 at age 80.

The study was funded by the US National Institutes of Health who are interested in learning more about aging in cold-blooded or cold-blooded species and applying it to people who are warm-blooded.

– It’s not metabolism –

Scientists have long held that ectotherms—because they need outside temperatures to regulate their body temperature and therefore have lower metabolisms—age more slowly than endotherms, which generate their own heat internally and have higher metabolisms.

This relationship holds within mammals. For example, mice have a much higher metabolic rate than humans and a much shorter lifespan.

Surprisingly, however, the new study found that metabolic rate wasn’t the key driver it had previously been thought to be.

“Although there were ectotherms that age slower and live longer than endotherms, there also exist ectotherms that age faster and live shorter lives,” after accounting for factors such as body size.

The study also raised intriguing clues that could point avenues for future research. For example, when the team looked directly at a species’ average temperature versus metabolic rate, they found that warmer reptiles age faster, while the opposite was true for amphibians.

A theory that turned out to be true: Animals with protective physical traits like turtle shells or chemical traits like the toxins that certain frogs and salamanders can emit lived longer and aged more slowly than those without.

“A shell is important for aging and it makes a turtle really hard to eat,” Miller said.

“This means that animals can live longer and evolution can work to reduce aging so that if they avoid being eaten, they still function well.”

A second study by a team from the University of Southern Denmark and other institutions applied similar methods to 52 turtle and tortoise species in zoo populations and found that 75 percent showed negligible ageing.

“If some species could truly escape aging and mechanistic studies could show how they do so, human health and longevity could benefit,” scientists Steven Austad and Caleb Finch wrote in a comment on the studies.

However, they found that some species, even if they do not show increasing mortality over the years, do show age-related infirmities.

Jonathan the turtle “is now blind, has lost his sense of smell and needs to be hand fed,” they said, proving that the ravages of time are for everyone.

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