Less sex plus more greens equals a longer life: Reptile study

A new study by Tel Aviv University researchers finds that reduced reproductive rates and a plant-rich diet increases the lifespan of reptiles. The research, published in the journal Global Ecology and Biogeography, was led by Prof. Shai Meiri, Dr. Inon Scharf, and doctoral student Anat Feldman of the Department of Zoology at TAU's Faculty of Life Sciences, in collaboration with Dr. Daniel Pincheira-Donoso of the University of Lincoln, UK, and other scientists from the US, the UK, Ecuador, and Malaysia.

The international team collected literature on 1,014 species of reptiles (including 672 lizards and 336 snakes), a representative sample of the approximately 10,000 known reptiles on the planet, and examined their life history parameters: 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, among other factors, early sexual maturation and a higher frequency of laying eggs or giving birth were associated with shortened longevity.

Putting the brakes on physical stress

"There were aspects of this study that we were able to anticipate," said Prof. Meiri. "Reproduction, for example, comes at the price of great stress to the mother. She experience physiological stress, is unable to forage efficiently, and is more vulnerable to her surroundings. This reflects evolutionary logic. 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.

"We found that reptiles that were sexually mature early on were less likely to make it to old age," Prof. Meiri continued. "Live fast and die young, they say -- but live slow, live long."

Eat your greens

The team also discovered that herbivores -- lizards with a plant-rich diet -- lived longer than similar-sized carnivores that ate mostly insects. Ingestion of a protein-rich diet seemed to lead to faster growth, earlier and more intense reproduction, and a shortened lifespan. Herbivorous reptiles were thought to consume nutritionally poorer food, so they reached maturity later -- and therefore lived longer.

Hunting may also be riskier than gathering fruits and leaves -- at least for animals, the researchers concluded. "If you're an animal, hunting your food can be dangerous," said Prof. Meiri. "You risk injury or even death. This is why you cannot simply transfer this logic to humans. 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."

The researchers also found correlates that suggested reptiles in geographically colder regions lived longer -- probably due to two factors: hibernation, which offers respite from predators, and slower movement due to a seasonal drop in metabolic rate. "Our main predictors of longevity were herbivorous diets, colder climates, larger body sizes, and infrequent and later reproduction," said Prof. Meiri. "I stress that you cannot simply transfer the results of a study on lizards to humans -- but 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."