Secrets of aging revealed in largest study on longevity, aging in reptiles and amphibians

At the age of 190, Jonathan the Seychelles giant tortoise recently made headlines for being the “oldest living land animal in the world.” While there is anecdotal evidence such as this that some species of turtles and other ectotherms — or “cold-blooded” animals — live long, the evidence is shoddy and mostly focused on animals living in zoos or a few individuals living in the wild. Now an international team of 114 scientists, led by Penn State and Northeastern Illinois University, report the most comprehensive study of aging and longevity to date, consisting of data collected in the wild from 107 populations of 77 reptile and amphibian species across the globe. worldwide.

Among their many findings, which they report in the journal today: Science, the researchers have documented for the first time that turtles, crocodiles and salamanders have particularly low aging rates and longer lifespans for their size. The team also found that protective phenotypes, such as the hard shells of most turtle species, contribute to slower aging and, in some cases, even “negligible aging” — or lack of biological aging.

“There is anecdotal evidence that some reptiles and amphibians age slowly and have long lifespans, but so far no one has studied this on a large scale in numerous species in the wild,” said David Miller, senior author and associate professor of population ecology. of wild animals. , Penn State. “If we can understand what causes 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.”

In their study, the researchers applied comparative phylogenetic methods — which enable research into the evolution of organisms — to mark and recapture data — in which animals are captured, tagged, released back into the wild and observed. Their aim was to analyze the variation in ectothermic aging and longevity in the wild compared to endotherms (warm-blooded animals) and to explore previous hypotheses regarding aging, including the mode of body temperature regulation and the presence or absence of protective Physical Characteristics.

Miller explained that the “thermoregulatory mode hypothesis” suggests that ectotherms — because they need external temperatures to regulate their body temperature and therefore often have lower metabolisms — age more slowly than endotherms, which generate their own heat internally and have a higher metabolism.

“People think, for example, that mice age quickly because they have a high metabolism, while turtles age slowly because they have a low metabolism,” Miller says.

However, the team’s findings reveal that the aging rates and longevity of ectotherms are both well above and below known aging rates for similarly sized endotherms, suggesting that the way an animal regulates its temperature — cold-blooded versus warm-blooded — is not necessarily indicative of the aging rate or lifespan.

“We didn’t find support for the idea that a lower metabolic rate means ectotherms age more slowly,” Miller said. “That relationship was only true for turtles, suggesting that turtles are unique among ectotherms.”

The hypothesis of the protective phenotypes suggests that animals with physical or chemical properties that provide protection, such as armor, spines, shells or venom, age more slowly and last longer. The team documented that these protective qualities cause animals to age more slowly and, in the case of physical protection, live much longer for their size than animals without protective phenotypes.

“It may be that their altered hard-shell morphology provides protection and contributed to their life history evolution, including negligible aging — or lack of demographic aging — and exceptional longevity,” said Anne Bronikowski, co-senior author and professor in Integrative Biology, Michigan State.

Beth Reinke, first author and assistant professor of biology, Northeastern Illinois University, further explains: “These different protective mechanisms can reduce the death rates of animals because they are not eaten by other animals. So they are likely to live longer, and that puts pressure on them.” to age more slowly. We found the greatest support for the protective phenotype hypothesis in turtles. Again, this shows that turtles as a group are unique.”

Interestingly, the team observed negligible aging in at least one species in each of the ectotherm groups, including in frogs and toads, crocodilians and turtles.

“It sounds dramatic to say they don’t age at all, but in fact their chance of dying doesn’t change with age once they are past reproduction,” Reinke said.

Miller added: “Negligible aging means that if an animal’s probability of dying within a year is 1% at age 10, if it is still alive at age 100, the probability of dying is still 1.” % is (1) In contrast, in adult females in the US, the risk of dying within a year is about 1 in 2,500 by age 10 and 1 in 24 by age 80. When a species has negligible aging (deterioration) aging just doesn’t occur.”

Reinke noted that the team’s new study was only possible thanks to the contributions of a large number of collaborators from around the world who studied a wide variety of species.

“By bringing together these authors, who have all spent years and years of work studying their individual species, we have been able to get these more reliable estimates of aging rate and longevity that are based on population data rather than just individual animals,” she said. said.

Bronikowski added: “Understanding the comparative landscape of animal aging may reveal flexible traits that could be worthy targets for biomedical research related to human aging.”