Why these types of animals barely age at all

By Mark Waghorn via SWNS

Animals such as turtles with bony shells, spines or venom age slower and some hardly at all, according to new research.

Scientists found that shields are more important than a low metabolism - shedding fresh light on the aging process.

Turtle shells contribute to slower and even 'negligible' aging - or lack of biological aging.

Many species of turtles and tortoises have also found a way to switch off senescent cells - zombie cells that stop dividing and cause disease.

Senior author Professor David Miller, of Penn State University, said: "Negligible aging means if an animal's chance of dying in a year is 1% at age 10, if it is alive at 100 years, its chance of dying is still 1%.

"By contrast, in adult females in the US, the risk of dying in a year is about 1 in 2,500 at age 10 and 1 in 24 at age 80.

"When a species exhibits negligible senescence or deterioration, aging just doesn't happen."

Co-author Professor Anne Bronikowski, of Michigan State University, said: "It could be their altered morphology with hard shells provides protection and has contributed to the evolution of their life histories, including negligible aging – or lack of demographic aging - and exceptional longevity."

The oldest land creature in the world is a giant tortoise in the Seychelles named Jonathan - he's 190 years old.

First author Dr. Beth Reinke, of Northeastern Illinois University, said: "These various protective mechanisms can reduce animals' mortality rates because they're not getting eaten by other animals.

"Thus, they're more likely to live longer, and that exerts pressure to age more slowly.

"We found the biggest support for the protective phenotype hypothesis in turtles. Again, this demonstrates that turtles, as a group, are unique."

The findings in the journal Science shed fresh light on why an 'elixir of youth' has proved so elusive for humans.

The international team observed negligible aging in at least one species of frog and toads, crocodiles and turtles.

Dr. Reinke added: "It sounds dramatic to say they don't age at all, but basically their likelihood of dying does not change with age once they're past reproduction."

Data was collected from 107 populations of 77 wild species of reptiles and amphibians across the world in the most comprehensive study of aging to date.

The analysis showed turtles, crocodiles and salamanders have particularly low aging rates and extended lifespans for their sizes.

Prof Miller said: "Anecdotal evidence exists that some reptiles and amphibians age slowly and have long lifespans, but until now no one has actually studied this on a large scale across numerous species in the wild.

"If we can understand what allows some animals to age more slowly, we can better understand aging in humans, and we can also inform conservation strategies for reptiles and amphibians, many of which are threatened or endangered."

A technique called phylogenetics - which shows how genetically similar organisms are - was combined with observations of animals that were captured, tagged and released.

It enabled a comparison between cold and warm-blooded animals - ectotherms and endotherms, respectively.

The former relies on external temperatures and often have lower metabolisms. It was believed they age more slowly than endotherms which generate their own heat.

Prof Miller said: "People tend to think, for example, that mice age quickly because they have high metabolisms, whereas turtles age slowly because they have low metabolisms."

But ectotherms' aging rates and lifespans were found to range both well above and below those known for similar-sized endotherms.

It suggests the way an animal regulates its temperature is not necessarily indicative of lifespan.

Prof Miller said: "We didn't find support for the idea a lower metabolic rate means ectotherms are aging slower.

"That relationship was only true for turtles, which suggests that turtles are unique among ectotherms."

On the other hand, animals with physical or chemical traits that confer protection were found to live much longer for their size.

The study was a huge global enterprise involving 114 scientists looking at a wide variety of species.

Dr Reinke said: "Being able to bring these authors together who have all done years and years of work studying their individual species is what made it possible for us to get these more reliable estimates of aging rate and longevity that are based on population data instead of just individual animals."

All living organisms age and die – there is no way of escaping death. But they follow different patterns of weakening and deterioration - counterintuitive as it may seem.

Added Prof Bronikowski: "Understanding the comparative landscape of aging across animals can reveal flexible traits that may prove worthy targets for biomedical study related to human aging."