The protective phenotypes hypothesis suggests that animals with physical or chemical traits that confer protection - such as armor, spines, shells or venom - have slower aging and greater longevity.
“That relationship was only true for turtles, which suggests that turtles are unique among ectotherms.” “We didn’t find support for the idea that a lower metabolic rate means ectotherms are aging slower,” said Miller.
The team’s findings, however, reveal that ectotherms’ aging rates and lifespans range both well above and below the known aging rates for similar-sized endotherms, suggesting that the way an animal regulates its temperature - cold-blooded versus warm-blooded - is not necessarily indicative of its aging rate or lifespan. “People tend to think, for example, that mice age quickly because they have high metabolisms, whereas turtles age slowly because they have low metabolisms,” said Miller. Miller explained that the "thermoregulatory mode hypothesis" suggests that ectotherms - because they require external temperatures to regulate their body temperatures and, therefore, often have lower metabolisms - age more slowly than endotherms, which internally generate their own heat and have higher metabolisms. Their goal was to analyze variation in ectotherm aging and longevity in the wild compared to endotherms (warm-blooded animals) and explore previous hypotheses related to aging - including mode of body temperature regulation and presence or absence of protective physical traits. In their study, the researchers applied comparative phylogenetic methods - which enable investigation of organisms’ evolution - to mark-recapture data - in which animals are captured, tagged, released back into the wild and observed. “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.” “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,” said David Miller, senior author and associate professor of wildlife population ecology, Penn State. 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. Now, an international team of 114 scientists, led by Penn State and Northeastern Illinois University, reports the most comprehensive study of aging and longevity to date, comprising data collected in the wild from 107 populations of 77 species of reptiles and amphibians worldwide.Īmong their many findings, which they report today (June 23) in the journal Science, the researchers documented for the first time that turtles, crocodilians and salamanders have particularly low aging rates and extended lifespans for their sizes. At 190 years old, Jonathan the Seychelles giant tortoise recently made news for being the “oldest living land animal in the world.” Although, anecdotal evidence like this exists that some species of turtles and other ectotherms - or ‘cold-blooded’ animals - live a long time, evidence is spotty and mostly focused on animals living in zoos or a few individuals living in the wild.
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