The greatest research of its type demonstrates that wild turtles mature gradually, live long lives, and identifies other species that essentially never age.
The 190-year-old gigantic tortoise from the Seychelles, Jonathan, has garnered news for being the "oldest living land mammal in the world." Even while there is anecdotal evidence that some turtle species and other ectotherms, or "cold-blooded" animals, live lengthy lives, this proof is patchy and mostly based on animals held in zoos or a tiny number of individuals that have survived in the wild. An multinational team of 114 scientists led by Penn State and Northeastern Illinois University just released the largest research on aging and longevity to date. It includes information acquired from 107 populations of 77 various species of reptiles and amphibians in the wild.
Given the first time, the researchers learned that salamanders, crocodilians, and turtles aged very slowly and had rather lengthy lives for their size. In the journal Science, they just just published their findings. The study team also found that protective phenotypes, such as the majority of turtle species' hard shells, result in slower aging and, in certain cases, even in the absence of biological aging.
There is anecdotal evidence that some reptiles and amphibians age slowly and live a long time, but no one has examined this issue extensively across a wide range of species in the wild up until now, according to senior author and associate professor of wildlife population ecology David Miller from Penn State. We can better understand aging in humans and develop conservation plans for reptiles and amphibians, many of which are vulnerable or endangered, if we can figure out what causes some creatures to age more slowly.
In their work, the researchers combined comparative phylogenetic approaches—which allow for the exploration of species' evolution—with mark-recapture data, which involves capturing animals, tagging them, releasing them back into the wild, and then watching them. Their goal was to compare the aging and longevity of ectotherms in the wild to endotherms (warm-blooded animals) and examine preconceived notions about aging, such as how body temperature is regulated and whether or not protective morphological characteristics are present.
According to Miller, the "thermoregulatory mode hypothesis" contends that endotherms, who internally produce their own heat and have greater metabolisms, age more rapidly than ectotherms, who depend on external temperatures to maintain their body temperatures.
For instance, Miller noted, "people frequently believe that mice age rapidly due to their high metabolisms, but turtles age slowly due to their low metabolisms.
However, the team's findings show that ectotherms' aging rates and lifespans vary considerably from those known for similar-sized endotherms, indicating that an animal's ability to regulate its body temperature, whether cold-blooded or warm-blooded, is not always a reliable indicator of that animal's aging rate or lifespan.
According to Miller, there is little evidence to support the notion that ectotherms age more slowly because they have lower metabolic rates. "That association was exclusively present in turtles, suggesting that they are distinct from other ectotherms."
According to the protective phenotypes theory, animals having physical or chemical characteristics that provide protection, such armor, spines, shells, or venom, age more slowly and live longer. The researchers found that animals with these protective characteristics do in fact age more slowly and, in the case of physical protection, live far longer for their size than those without them.
According to Anne Bronikowski, co-senior author and professor of integrative biology at Michigan State, "It could be that 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."
According to Beth Reinke, lead author and associate professor of biology at Northeastern Illinois University: "These different protection systems can lower animal death rates because they prevent them from being eaten by other species. They have a higher likelihood of living longer, which puts pressure on them to age more slowly. Turtles provided the strongest evidence for the protective phenotype hypothesis that we could find. Once more, this highlights how distinctive turtles are as a group.
Intriguingly, the researchers discovered that at least one species in each category of ectotherms, including turtles, crocodilians, and frogs and toads, showed minor signs of aging.
"It seems dramatic to claim that they don't age at all, but basically, after they're past reproduction, their chance of dying does not alter with age," said Reinke.
According to Miller, "Negligible aging means that if an animal is alive at age 100, its probability of dying is still 1 percent, even if its likelihood of dying in a year is 10% at age 10. In comparison, the chance of death in a year for adult females in the U.S. is around 1 in 2,500 at age 10 and 1 in 24 at age 80. Aging simply doesn't occur when a species demonstrates little senescence (deterioration).
Reinke pointed out that the team's innovative work was only made possible thanks to the participation of several international partners who were researching a wide range of species.
We were able to obtain these more trustworthy estimates of aging rate and longevity that are based on population data rather than simply individual animals because we were able to gather these writers together who have all spent years and years studying their own species.
Understanding the comparative landscape of aging in many animal species might identify adaptable features that can represent worthwhile targets for biological research into human aging, according to Bronikowski.
