A quiet backwoods study opens a huge window on aging.
Originally published in Discover.
WHEN JUSTIN CONGDON WAS A TEENAGER, he spent his days in the woods of northeastern Pennsylvania, shooting pheasants and trapping muskrats so he could sell their pelts for $4 apiece. He would have laughed had anyone told him he might spend the rest of his life in a forest preserve trapping turtles, X-raying their bellies, and painstakingly gluing their shells back together when they had the bad luck to be hit by cars.
But that’s precisely what he’s doing on this late May afternoon at the University of Michigan’s E. S. George Reserve, as he has done every spring and summer for 27 years. Carrying a leather tool belt with a makeshift rectal thermometer, needle-nose pliers, and black Sharpie pen, he patrols East Marsh, an 11.5-acre habitat with water lilies and wild irises. Most of the time he’s on the lookout for female turtles—Blanding’s, Common Snapping, and Midland Painted—abundant with fertilized eggs and ready to unload them on the first warm day. A low plastic fence separates the turtles’ marshland habitat from the higher, drier ground where they build their nests. For 16 hours Congdon circles the marsh, following the fence that keeps the turtles from escaping. Any gravid—pregnant—female that wants to leave the marsh must make a small contribution to science before she’s permitted to seek out a place to lay her eggs on the other side of the fence.
He spots a Midland Painted searching for a way past the barrier. She has the characteristic bright red trim around the edges of her shell and the intricate lined pattern, almost like a cave drawing, underneath. He picks her up and pops his thermometer in her cloaca, the chamber in her tail where the digestive, urinary, and reproductive organs come together. She flails her legs wildly and voids water onto Congdon’s hands, but he gets his reading, a useful piece of information for understanding how the turtle manages the heat it needs to carry out reproduction and other biological functions. With the Sharpie, he marks her underside, or plastron, with body temperature, time, and location, tosses her into a camouflage-colored bag, and strides quickly back to his turtle-processing shed, a former military radar outpost that has become the border patrol for wandering reptiles.
In this primitive two-room shed, Congdon has conducted some of the most sophisticated life-history studies of long-lived vertebrates—research that could upend our theories about how animals grow old and might one day help unlock secrets of human longevity. For 49 years scientists have cataloged more than 12,000 turtles living on the reserve, compiling a huge database of individual reptiles. Each new capture has its shell marked for identification, and all animals are weighed, measured, and inspected for disease or injury. Gravid females are X-rayed to determine how many eggs they’re carrying and how big they are. Nests are tracked and locations recorded. During peak season, the shed sometimes looks like a turtle traffic jam, and processing can take until 2 a.m.
Today’s catch is a 16-year-old female that has been caught and X-rayed five times since she first reproduced in 1996. Some of the turtles that show up at the shed are much older; although tagged as adults in the 1950s, they are still healthy and fertile. They’re also the key to Congdon’s groundbreaking discovery: Blanding’s and perhaps also Midland Painted turtles don’t senesce—deteriorate physically—as they grow old. They simply don’t age. And Congdon says the females actually produce more eggs as they grow older: “They’re crankin’ compared to the young ones.” When they do die, the cause is often an attack—hit by a car or mauled by a raccoon—or one of a number of infectious diseases that kill these turtles at all ages in seemingly equal proportions. While certain ailments, such as cancer and heart disease, strike older humans more often than they do younger ones, Congdon’s animals don’t seem to become more vulnerable to disease as they grow older.
The findings are turning the discussion of aging in mammals upside down. “His work is a sharp challenge to a theory that has been taken at face value—that senescence is inevitable,” says Caleb Finch, professor of biological sciences and gerontology at the University of Southern California. “Here you have a vertebrate turtle that shows no increase in mortality and no loss of reproductive capacity at ages where mammals, including humans, will shut down totally.” Other species with long life spans include sharks, tarantulas, and rockfish, and human gerontologists are starting to pay close attention. As Huber Warner, associate director of the Biology of Aging Program at the National Institute of Aging, says, “If we knew what regulates life span in turtles, that might be useful in figuring out how humans age and how to intervene.”
THE FIRST THING YOU NOTICE ABOUT JUSTIN CONGDON, other than his deeply creased face and wild gray beard, is his passion for telling one bravado-tinged story after another, preferably over a cold Budweiser. Sit long enough and you’ll hear about his adventure on a runaway logging truck while collecting lizard blood in the jungles of Mexico, an accident in which he almost lost a hand. Or he’ll tell you about his run-in with a particularly testy Banded Water Snake that he spotted one evening while walking along the fence at the Michigan reserve. The snake had been tagged by a graduate student, but “I hadn’t brought a flashlight. So I grabbed the snake and flipped its head back and pulled the tail up to read the ID. I didn’t see, because it was getting dark, that the snake had pulled its head free, and it bit me in a wide-open eye.”
The impression he creates is that of someone who lives far more happily outside polite society, someone who is simultaneously a meticulous biologist and a swashbuckling cowboy. Both images of himself seem to grow from the same impulse—the desire to dwell in unfettered wilderness, in places where people don’t sip champagne. “A few years back, Gianni Versace was killed in Florida,” says Mike Plummer, a biologist at Harding University in Searcy, Arkansas, who was eating dinner with Congdon the night the fashion designer was murdered. “Somebody came out on the news and said, ‘Tonight the world mourns for Versace.’ Justin said, ‘Can you believe that? The world mourns for the death of a guy who sews pants?'”
The two sides of Congdon’s temperament—researcher and cowboy—fit naturally together, but they didn’t always. Growing up in a military family, he had almost no interest in his studies and couldn’t wait to come home from school to explore the swamps and woods near his house. Muskrats and water snakes held a fascination for him that classrooms and books did not. He assumed he would follow in his father’s footsteps and pursue a career in the Navy, but three years of scrubbing toilets and cleaning guns on an aircraft carrier persuaded him to try college. The thought of returning to school scared him so much that as he drove to Victorville, California, to enroll in a junior college, he kept saying over and over to himself, “I hope I never get there.”
Just one biology class convinced Congdon that he could make a living pursuing his childhood fascinations. At 26, while working toward a master’s degree in biology, he moved into an abandoned copper and silver mine in the Mojave Desert, which he furnished with cast-off carpeting and a propane refrigerator in order to study how kangaroo rats and pocket mice use different desert habitats seasonally. For four days at a stretch, he’d trap intensively on one-quarter of his grid. The work was so intense that he had to stop and take a break, hiking the Providence and Granite Mountains; then he’d return to trap another quarter. At night he’d read by taillights salvaged from an abandoned car and hooked up to the battery of his Volkswagen bus. “I hated going near civilization,” he says. “I promised my parents that I’d call them every time I went out for supplies, and I did. But there were two-week periods when they didn’t hear from me.”
In 1975 his mentor at the University of Michigan, evolutionary ecologist and herpetologist Donald Tinkle, offered him a job on the E. S. George Reserve. The day Congdon and his wife arrived, carting all their belongings with them, Tinkle announced he was flying off to Utah to work on another study. “I said, ‘You’ve got to be kidding,'” Congdon recalls. “I thought, ‘My God, how am I going to handle this?’ We left the truck half-unloaded, and Don and I went down to the swamp and checked traps, and he showed me the marking codes and where the equipment was, and then he left.”
Once he had absorbed his new responsibilities, Congdon’s days fell into a pleasant routine, canoeing in the wetlands to collect data on the residents. “I started trapping some marshes that hadn’t been trapped, and we had a 100-turtle day when I went into East Marsh for the first time. At that point I think Don knew we were going to have a good study.”
Tinkle died five years later, at 49. “I was devastated,” Congdon says. “He was my mentor and academic hero.” Just before his death, Tinkle called the National Science Foundation, announced he was terminally ill, and obtained permission for Congdon to run out the grant. The younger scientist vowed to oversee the project in a way that would honor his predecessor. “I wanted it to be run as good as it had been run, or better,” he says. “I couldn’t have had it any other way.”
While crunching his data in the mid-1980s, Congdon made a startling discovery: The oldest female Blanding’s Turtles—more than 50 years old—had more egg clutches than younger ones, as well as more eggs per clutch. Not only that, they died at a lower rate too. “What did I do wrong?” Congdon remembers thinking to himself. “Did I make a mistake? Did I analyze it incorrectly?” He knew that adult turtles kept growing throughout their lives, and so he wondered whether the true variable might be body size rather than age. Once he ran the numbers again, controlling for body size, he was astonished to find that he got nearly identical results.
At first, he didn’t write up the findings. There was little or no conversation among gerontologists about nonhuman aging models. “I just couldn’t get anybody interested in what I was doing,” he says. So he resolved to bide his time, figuring that the more data he collected, the stronger his evidence would be.
AS HUMANS SENESCE, ARTERIES HARDEN, eyesight deteriorates, vital organs lose capacity, reproduction stops, and the probability of death increases. For us, this progression makes evolutionary sense: Since we spend almost two decades raising children, it behooves us to finish producing them while we’re still young. Our genes favor early childbearing; they also ensure that we’ll be around long enough to raise our kids.
It also behooves creatures like mice and rats to have babies early in their lives but for a different reason: If they don’t, they might get eaten before they reproduce. “Even if a mouse was immortal as far as physiological death, a predator would still get it within three or four years,” says Whit Gibbons, an ecologist at the Savannah River Ecology Laboratory in Aiken, South Carolina, the facility where Congdon works during the part of the year that he’s not in Michigan. “Therefore, their genes operate very well at the early stages of their lives. There’s no sense having a gene in a mouse that’s going to work in 10 years, because there’s no way those genes will be passed on.”
And mice are among a group of short-lived animals, which includes worms, lizards, and fruit flies, that scientists have traditionally used to study aging. With short-lived animals, “you can walk away from a project within three or four years, and you’ve got a lot of data, and you can make a big impression on your colleagues,” says Ronald Nussbaum, a zoologist at the University of Michigan. Under such pressures, turtles are hardly the research subject of choice.
Why don’t turtles operate like mice? One reason is their shell, which makes them less vulnerable to predators. At the same time, because they spend much of their early years developing their shells, they delay sexual maturity. Because turtles begin reproducing so late, and the vast majority of their young don’t survive, evolution favored those individuals that were able to keep pumping out eggs. (See “Save the Grown-ups if You Want Babies” on this page.)
With the Blanding’s Turtles in particular, not only are the old females still fertile, they’re often more productive and have a higher survival rate than their daughters and granddaughters. Congdon’s theory: Age brings wisdom, even in reptiles. “Blanding’s Turtles know a lot about the landscape that they live in,” Congdon says. “I’m not just talking about the immediate landscape. We have animals that travel four kilometers [2½ miles] to nest. Do they know where they are when they are four kilometers away from where they started out? Yes. Did they have some innate, built-in map? No, they learned that route over years and years. So if a female goes to a place and it is not a successful nesting site, the old ones know where to find the next-best place better than the young ones. When you make it to your sixties with no doctors, you are the best of the best. Certainly, you can get run over by a mower. But maybe older females have a slight edge in avoiding risk.”
He knows this is hard for many people to believe. “When you dissect a turtle’s brain, you just go, ‘Boy, there is not a lot of room in there for a lot of thought.’ I mean, they are tiny, tiny brains. But I think these turtles are way smarter than we give them credit for.” When Congdon retires and has enough time, he’d like to “train turtles to see how much they can learn. I think they could learn a lot.”
WHILE CONGDON IS DEVELOPING LIFE-HISTORY DATA on individual captures, other researchers are trying to get a better grasp on why the animals resist senescence. “The turtles are vertebrates, so they’re reasonably closely related to us,” says Steven Austad, professor of biology at the University of Idaho. “To the extent that, on a cellular level, these turtles show resistance to the stresses that damage human cells, they might have something to teach us.”
James Christiansen, professor of biology at Drake University in Des Moines, is studying how telomeres, the simple, non-genetic DNA sequences that sheathe the ends of chromosomes, function in reptiles. Each time a healthy human cell divides, it loses a little bit of the telomere, until the strands are too short to protect the chromosomes. At that point the DNA in a cell begins to break down, which triggers senescence and death. Human cancer cells go off the program, producing an enzyme called telomerase that stops the shortening and renders the malignant cells immortal.
Turtles seem to follow a different pattern. “Even though many species live in some of our most polluted environments,” Christiansen says, “they avoid cancer.” Early results of his study suggest that some reptiles may receive a short burst of telomerase early in life, which makes healthy cells rather than cancerous ones immortal. If this proves to be the case, he says, the human implications may be dazzling. “If we could do that with humans shortly after birth, before the mutations have a chance to creep in,” he says, “we could potentially add a hundred years to the human life span.”
AT 61, CONGDON IS INCREASINGLY AWARE OF HIS OWN AGE. “I feel it,” he says. “I don’t think a lot about it. I feel it in terms of not being able to go and go and go without paying. I smile when the old Blanding’s ladies look at me, and I imagine them saying, ‘OK, go ahead, bother me today, but I’m going to outlive you.'” Congdon also fears the turtles will outlive the Michigan study. He plans to return to the reserve for five more summers—but will there be anyone to take over after he retires? “I have been told how valuable the research is,” he says. “I’ve been told how a number of people want my data. I have yet to be told, ‘I want the work.’ So I don’t have anybody on the horizon.”
Today, though, he has more pressing concerns, like the fact that the late-spring chill seems to be stopping the turtles from building nests. About a half hour ago, he airlifted a 19-year-old female, tagged with a large number 5, over the East Marsh fence to build her nest, but he’s concerned about the cloud cover and approaching cold. “She’ll either commit really quick, or she won’t,” he says. “When the temperature goes down, all the biological processes—strength, muscle coordination, ability to export oxygen to the legs—go down.” No. 5 makes her way up the side of an old gravel pit, finds her spot, and starts digging, but then hits a root and abandons the unfinished nest. She slowly inches farther up the hill, but the air has cooled noticeably. She gives up.
Back at the turtle shed, Congdon hears better news. Jason Sweas, his undergraduate assistant from the University of Michigan, has witnessed the first successful nesting of the season, on a lawn near the entrance gate. For an hour he watched as a Midlands Painted Turtle lowered her back end into the hole, laid her eggs, then spent an eternity covering them. She stretched one hind leg as far as it would go, then the other, with each stroke pulling some more soil back over the nest until her efforts were almost invisible. When she was finished, Sweas captured her and carried her to the shed.
He also brought a young male he had spied lumbering around with his shell cracked after he was hit by a car. “The spine’s not broken,” Congdon notes, so he cuts a four-inch strip of black electrical tape, applies it to the broken carapace, then spreads an adhesive over the tape. “The epoxy will hold it together until the bone grows back. Then it will fall off,” he explains. “My guess is that we’ll see this guy, with a slightly damaged carapace, years from now. I guess, technically, we shouldn’t do this stuff. But I don’t think we’ve changed the demography in any measurable way. If I could measure that accurately, I’d be a very happy guy.”
It’s time to think about knocking off work and having a beer. The successful nester and the injured male will live in Congdon’s utility-room sink overnight and be returned to their swamp home in the morning. Before settling in for the evening, though, Congdon walks East Marsh one last time. He releases No. 5, and she swims back into the marsh, presumably to lay her eggs another day. Congdon watches her as she paddles through the water. Despite his insistence that he has no emotional attachment to his subjects, there’s a look in his eyes that conveys the gruff affection he has developed for the critters.
Verbally, though, he concedes nothing. “Another day,” he says simply. “Another turtle.”
SIDEBAR: Save the Grown-ups if You Want Babies
WHEN WE THINK OF TURTLE CONSERVATION, we think of “head start” programs, in which nests are protected from predators and hatchlings are raised in captivity until the animals are old enough to survive in the wild. Meanwhile, adults are harvested on a regular basis, for the pet trade and for their supposed medicinal value. Justin Congdon’s research is making a lot of people see that this scenario may be upside down: Hatchlings need protection, but adults need it even more.
“If you’re interested in conserving long-lived species, what is your best strategy?” asks zoologist Ronald Nussbaum. “Most of the turtles’ mortality occurs in the first year. Most of the eggs never make it. If a turtle produces 1,000 eggs, 998 of them can die as long as two of them, one male and one female, survive to replace her. So what would a conservationist do with this information? Well, you would make sure the adults survive and not worry too much about the nests and the eggs.”
There’s a reason wildlife managers haven’t thought in those terms: Most of the animals we try to protect, such as deer, rabbits, and quail, are relatively short-lived. “With deer, you can eliminate 50 percent of the population, and two to three years later, you’re back to where you were,” says ecologist Whit Gibbons. “With turtles, they won’t be anywhere near where they were. It takes so long for them to reach maturity that once you have an adult, you have a valuable commodity.” Gibbons says protecting the adults makes sense for other long-lived species too. “This has immediate application—for whales, for elephants, for polar bears—for animals that live a long time and can’t sustain the cropping they get.”