The oldest bats today are not supposed to exist. Gram for gram and pound for pound, they are downright tiny mammals; according to the evolutionary rules that apply to all species, they should be short-lived, like other small-bodied creatures.
And yet, many of Earth’s winged mammals buck this trend, sometimes topping out decades past their anticipated expiration date. One species, Brandt’s bat, which weighs only four to nine grams as an adult, the entire weight of a quarter, has been recorded to survive to 41 years in the wild, about as long as a standard Asian elephant. four tons, and almost 10 times longer than its body dimensions would predict. “It’s incredibly long-lived for its size,” says Jerry Wilkinson, a biologist at the University of Maryland. “Longest than any other mammal.”
No single factor can explain the amazing longevity of bats. They are intelligent and collaborative, and their super-powerful immune systems help them tolerate viruses that make other animals disastrously ill, traits that no doubt help them survive. But one of his anti-aging tricks, one of the most biologically elusive in the world, is to simply postpone aging for months each year.
As autumn plunges into winter, the small mammals huddle in caves, trees and mines, folding their wings and dangling their feet over their heads. His body temperature plummets, sometimes approaching freezing point; your heart rate drops to a handful of beats per minute; they hardly breathe at all. “They basically shut down your entire body, drastically reducing all the functions that we normally associate with life,” says Aline Ingelson-Filpula, a biologist at Carleton University. Hibernation spans like these have long been understood as almost suspended animation, used to conserve the body’s resources in times of great need. For bats, Wilkinson and his colleagues found that it can also dramatically extend their stay on Earth.
Time, per se, is not really what kills us; it is how we spend it that affects us. For most creatures, the calendar of days and months keeps pace with the internal aging process. But bats, and probably other hibernating animals as well, are able to decouple those clocks effectively, advancing their biological age only when they are active and awake, even as their chronological clock ticks forward. “Think of hibernators as being turned off,” says Hanane Hadj-Moussa, a biologist at the Babraham Institute. “They don’t get damaged as much as an organism that has to deal with life.”
Many scientists think of aging as what happens when the body accumulates the wear and tear of life: the costs of metabolizing food and burning it through daily energy demands, the slimy buildup of cellular waste. Hibernation brings those cumbersome processes to a near halt. The animals that handle it “do hardly anything metabolically and are very cold,” says Jenny Tung, a biologist at the Max Planck Institute for Evolutionary Anthropology. It’s calorie restriction and cryopreservation all in one, a slowdown that preserves physiological battery life, like switching an iPhone to low-power mode.
Scientists first became aware of the notion that hibernation might be a way to temporarily delay death in the early 1980s, when a team of Harvard medical researchers discovered that Turkish hamsters that spent time especially long in a seasonal pseudo-sleep perished later from their colleagues. In the years that followed, researchers quickly identified several other creatures that belonged to the Wake Less, Live More Club. Among them were ground squirrels, bats, marmots and lemurs, all of which outlive similar species that don’t hibernate, clear indications that the hibernators were somehow “cheating,” says Gabriela Pinho, a biologist at the Ecological Research Institute. in São Paulo, Brazil.
But definitively defining hibernation as an anti-aging ploy is difficult. If animals hide in burrows for months of the year, they are also often better hidden from predators and more protected from the elements. To confirm that these periods of inactivity were actually, at the molecular level, hitting the “Pause” button in the animals’ inevitable march to death, Tung told me, scientists needed a way to “start wondering what’s going on inside of the cells themselves.
This year, two groups of researchers, led by Pinho and Wilkinson, respectively, published some of the most compelling data on that front to date, on yellow-bellied marmots and great brown bats. Both studies scoured the genomes of small mammals looking for epigenetic modifications: molecular punctuation marks that annotate stretches of DNA, making them more or less easy to read. These markings blend and spread out more as we age, and researchers have studied them closely enough to read their patterns, almost like tree rings, and determine how far our tissues have progressed along the path to old age When researchers then compare that to the actual number of years an animal has lived, they can get a sense of whether a creature is, molecularly speaking, particularly agile for its chronological age, says Danielle Adams, a Towson University biologist who worked with Wilson. in the great brown bats.
By inspecting the genomes of marmots and bats at different times of the year, Pinho, Wilkinson, Adams and their colleagues were able to show that in the winter, the animals’ biological aging effectively stopped, even when they accumulated months of chronological time, then rapidly. they recovered in the spring when they woke up. The differences in DNA modifications were marked enough between seasons to be visible “within six months in the same individual,” says Isabel Sullivan, who was part of Wilkinson and Adams’ team.
Hibernation, to be clear, did not manifest itself just to fill nature with geriatric marmots and bats. Their primary goal is to rescue animals from almost certain death during resource-poor and often cold times of the year. “It’s a survival mechanism, just moving on to the next stage,” says Liliana Dávalos, a biologist at Stony Brook University. Perhaps it was a happy accident that these freeze frames also served as the fountain of youth.
Humans have other ways of surviving harsh winters: we have never needed hibernation to survive. But the prospect of mimicking the act still tugs at our brains. It could buy time for emergency surgeries. It could enable far-reaching space travel, keeping astronauts alive until they reach their destinations, while largely eliminating the need to pack tons of food. If longevity is also an advantage, some people are likely to fall in line.
Still, “I’d be cautious about saying that if we hibernate, we could double our lifespan,” Wilkinson said. Many species hibernate and still die at roughly the age predicted by their body size. And as comfortable as hibernation may seem, it threatens to collect a tax. While they are inactive, the animals’ brain function fails, their weight plummets, and their digestive tracts wrinkle. They stop almost all movement and their reflexes slow down, making them easy prey for predators that come across them and increasing the risk that their muscles will atrophy and their bones will demineralize. The power of the immune system also decreases, making bodies very susceptible to infection. (That’s a big reason why, in recent years, hordes of bats have been brought down by white-nose syndrome, a deadly fungal disease that hits hibernators hard.) Creatures that have evolved to hibernate have also devised many strategies to offset their costs, allowing them to recover each spring. Humans, however, haven’t, which means the cost would be much higher for us.
Even preparing for hibernation is arduous. In the fall, squirrels and bears before hibernation have to eat themselves into a diabetic coma to accumulate enough fat for several months. Yellow-bellied marmots, which can hibernate for up to eight months a year, have only “four or five months to basically double their weight and reproduce,” Pinho told me, condensing their most important tasks into the brief periods during which I’m awake ( Their young must also eat frenziedly shortly after birth, or risk dying in their first winter underground.)
Hibernation also cannot guarantee restful sleep. Most mammals must wake up, usually once every two weeks or so, to eliminate waste, perhaps drink a little water and, ironically, sleep. These awakenings are hugely expensive: “Each awakening a squirrel does consumes about 5 percent of the energy it uses during the entire hibernation season,” Ingelson-Filpula of Carleton University told me. The torpor etiquette is also… different. Some male bats wake up in the dead of winter to have sex with still-sleeping females, who may wake up weeks later to find themselves carrying a stranger’s sperm.
And then there’s all the FOMO. Hibernation “would be a way of looking at the world in the future, and that’s an attractive thing to think about,” Wilkinson told me. “But then you lose the opportunity to see things now.” Tung also would not want to miss any opportunity to “see my parents grow old or my children grow up.” You might think of hibernation as getting as close to death as possible without completely succumbing to it. If that’s really the price bats and groundhogs must repeatedly pay to prolong their years, maybe they don’t actually live that long.
Source: www.theatlantic.com