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. Now, an international team of 114 scientists 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.
Among their many findings, reported in June 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. 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.
“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. “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.”
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. 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.
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.
“We didn’t find support for the idea that a lower metabolic rate means ectotherms are aging slower,” said Miller. “That relationship was only true for turtles, which suggests that turtles are unique among ectotherms.”
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. The team documented that these protective traits do, indeed, enable animals to age more slowly and, in the case of physical protection, live much longer for their size than those without protective phenotypes.
Miller added, “Negligible aging means that 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% (see * below). By contrast, in adult females in the U.S., 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 (deterioration), aging just doesn’t happen.”
The National Institutes of Health supported this research.
Among their many findings, reported in June 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. 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.
“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. “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.”
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. 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.
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.
“We didn’t find support for the idea that a lower metabolic rate means ectotherms are aging slower,” said Miller. “That relationship was only true for turtles, which suggests that turtles are unique among ectotherms.”
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. The team documented that these protective traits do, indeed, enable animals to age more slowly and, in the case of physical protection, live much longer for their size than those without protective phenotypes.
Miller added, “Negligible aging means that 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% (see * below). By contrast, in adult females in the U.S., 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 (deterioration), aging just doesn’t happen.”
https://www.psu.edu/news/research/story/secrets-reptile-and-amphibian-aging-revealed/
AR #126
Living for Centuries
by William B. Stoecker
