Secret to longevity 6 October 2015

On the trail of the secret to longevity


​For lizards and snakes, a slow pace of life seems to be the secret to longevity, according to a multi-country study led by Israeli scientists.
Sand lizard
Copyright: Photo: George Chernilevsky/Wikimedia Commons
By Avigayil Kadesh
Snakes and lizards live longer when they reproduce less and eat more greens, according to the findings of an international team of researchers.
Zoologists from Tel Aviv University (TAU), in collaboration with colleagues in the United Kingdom, United States, Ecuador and Malaysia, came to this conclusion after analyzing collected literature on 1,014 species of reptiles -- 672 lizards and 336 snakes – as a representative sample of the approximately 10,000 known reptiles in existence today.
Taking into account factors including body size, earliest age at first reproduction, body temperature, reproductive modes, litter or clutch size and frequency, geographic distribution and diet, the researchers found that early sexual maturation and a higher frequency of laying eggs or giving birth were associated with shortened longevity, as were a plant-based diet, colder living conditions and larger body size.
"There were aspects of this study that we were able to anticipate," said Prof. Shai Meiri of TAU's Faculty of Life Sciences. "Reproduction, for example, comes at the price of great stress to the mother. She experiences physiological stress, is unable to forage efficiently, and is more vulnerable to her surroundings. This reflects evolutionary logic.”
As he points out, human mothers face similar conditions. “To relate this to humans, imagine the physical stress the body of an Olympic gymnast experiences — and the first thing that disappears is her period. In reptiles, it also increases the probability of being preyed upon.”
Another factor in longevity that came to light through the researchers’ analysis: reptiles living in geographically colder regions seem to live longer. They theorize that two key factors may be responsible: hibernation, which offers reptiles respite from predators; and slower movement due to a seasonal drop in metabolic rate.
"Live fast and die young, they say — but live slow, live long," Meiri observed.
Eat green and hibernate
The cross-continental research team also discovered that diet plays a significant role in longevity.
Lizards with a plant-rich diet live longer than similar-sized carnivores that eat mostly insects, presumably because the herbivores reach sexual maturity later. By comparison, reptiles with a protein-rich, carnivorous diet seem to grow faster and experience earlier and more intense reproduction – as well as a shortened lifespan.
Meiri says it’s possible that the greater physical risks involved in hunting for animal-based nutrition contribute to an earlier death. "If you're an animal, hunting your food can be dangerous," he said. "You risk injury or even death.”
For humans, he added, modern conditions have cancelled out this difference. “You cannot simply transfer this logic to humans,” he said. “Going to buy a head of lettuce at the supermarket is just as risky as going to the meat department. As a reptile, if you eat plants, you may need to be frugal, take life more slowly, and save your calories for digestion. You are forced to have a slower life, a more phlegmatic existence."
"Our main predictors of longevity were herbivorous diets, colder climates, larger body sizes, and infrequent and later reproduction,” Meiri summarized.
He stressed that the study’s conclusions do not necessarily correlate to human beings, and we don’t yet know how they correlate to other members of the animal kingdom.
"This is the first study of its kind on reptiles, which does open up an avenue for further research on other factors that lead to longevity of these and other species," said Meiri, whose lab focuses on the evolution and ecology of terrestrial vertebrates. He teaches both undergraduate and master’s students in zoology, including courses in macro-ecology and biogeography.
The reptile longevity research,published in the journal Global Ecology and Biogeography under the title “Late bloomers and baby boomers: ecological drivers of longevity in squamates and the tuatara,” was led by Meiri, Dr. Inon Scharf and doctoral student Anat Feldman of the TAU department of zoology, and carried out in collaboration with Dr. Daniel Pincheira-Donoso of the University of Lincoln, UK, and scientists from the Universiti Malaysia Sarawak, Pontificia Universidad Católica del Ecuador, Villanova University (Pennsylvania), Virginia Commonwealth University, University of Oxford and the Zoological Society of London.
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