Turtles & Tortoises & Negative Senescence

A giant Galápagos tortoise, only as old as it feels. Meridith Kohut for The New York Times

When I learn a new word–even if it is a word I cannot picture using in conversation but it represents a concept that is interesting and surprising, I consider that a good day. Jack Tamisiea, thanks for the science reporting here, and especially for the word senescence:

Tortoises and turtles don’t just live for a long time — they barely age while they live.

The black marsh turtles displayed negative rates of senescence, meaning their mortality risk decreased as they aged. iStock/Getty Images

For mammals like humans, aging is inevitable. No matter how many vitamins we take, skin sags, bones soften and joints stiffen over time. However, turtles and tortoises age more gracefully. Despite their wrinkled skin and toothless gums, species like Galápagos giant tortoises seem unscathed by the ravages of aging. Some show few signs of slowing down as they plod into their 100s.

To determine what drives these ageless wonders, two groups of researchers examined turtles, tortoises and their ectothermic, or coldblooded, brethren in a pair of studies published Thursday in the journal Science. Prior aging research has largely revolved around warm-blooded animals like mammals and birds. But ectotherms like fish, reptiles and amphibians dominate the longevity record books. For example, salamanders called olms slither through subterranean caves for nearly a century. Giant tortoises can live twice as long — earlier this year, a Seychelles tortoise named Jonathan celebrated his 190th birthday.

In one of the new studies, researchers compiled data sets on 77 species of wild reptiles and amphibians including Komodo dragons, garter snakes and tree frogs. The team utilized decades of monitoring data to analyze traits like metabolism to determine their impact on aging and longevity.

“We had these awesome data sets to get at questions of aging in a way that hasn’t been done before,” said Beth Reinke, an evolutionary biologist at Northeastern Illinois University and an author of the new study. “Getting at the heart of the issue of how aging evolves can only be done with this broad taxonomic approach.”

Living so long requires a gentle aging curve. After most animals reach sexual maturity, much of their energy is devoted to reproduction at the expense of mending aging tissue. This physical deterioration, or senescence, often causes an uptick in mortality risk as older animals become susceptible to predators or disease. But several coldblooded animals experience little senescence as they age…

Read the whole article here.

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