Clinging to rock piles high in the Pyrenees, the plant Borderea pyrenaica has a modest lifestyle: It grows a new shoot every summer, flowers and fruits, then sheds its aboveground growth to survive the winter as a tuber. What's remarkable is how long this life lasts for. Individual plants have been known to live 300 years or more. Scientists headed up into the mountains to find out whether these plants, in all their years of living, ever actually get old.
"Senescence" is what we usually call aging--getting weaker and closer to death as we get on in years. To us humans, it seems like a fact of life. But some other animals are thought to be "negligibly senescent." Certain fish, turtles, and other sea creatures seem to be perfectly healthy and fertile at 100 or 200 years old; they're no more likely to die at that age than at any other. Some plants, and especially some trees, may have nearly unlimited lifespans.
Scientists--not to mention cosmetics companies--would love to know exactly why humans are stuck with senescence while organisms like the bristlecone pine just get more fabulous with age. Unfortunately, it's difficult for those of us with limited lifespans to study those without. To squeeze some secrets out of Borderea pyrenaica, scientists from Spain and Sweden studied two populations of the plant over the course of five years.
Because Borderea pyrenaica is left with a scar on its tuber when each year's growth dies back, researchers could count the scars to calculate an individual tuber's age. Each year, they counted and measured the leaves on each plant. They also counted the plants' flowers, fruits and seeds. Since the plants come in male and female versions, the researchers would be able to compare aging in both--would the metabolic effort of making fruits and seeds take a toll on female plants' lifespans? At the end of the study, the researchers dug up all the tubers, dried them and weighed them. (Aesop says: Don't be jealous of negligibly senescent organisms. If old age doesn't kill you, science will!)
The researchers were able to calculate the age of almost 750 plants that were up to 260 years old. They found that tubers grew in size each year, reaching their maximum size after 50 or 100 years (depending on the population). As the tubers grew, the shoots that they put out each year got bigger too. After they reached about 60 years old, the plants didn't seem any more likely to die with the passing years. If anything, survivorship seemed to increase in old age. There was no difference between male and female plants.
As they got bigger, both types of plants put out more flowers, giving them greater potential to contribute to the next generation. This meant that the plants' "reproductive value"--an individual's expected fertility from its current age onward--actually increased over their entire lifespan.
It seems unlikely that we'll one day tap into some biological secret that enables us to live forever. But further research into the plants and animals that don't deteriorate with age might help us solve the mysteries of our own mortality. We may not ever become ageless, but we could learn to age with some of the grace of a lobster, or a mountain tuber.
Garcia, M., Dahlgren, J., & Ehrlén, J. (2011). No evidence of senescence in a 300-year-old mountain herb Journal of Ecology DOI: 10.1111/j.1365-2745.2011.01871.x
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