We have completed maintenance on DiscoverMagazine.com and action may be required on your account. Learn More

Can Turtles Live Forever?

A quiet backwoods study opens a huge window on aging.

By Barry Yeoman and Morad Bouchakour
Jun 1, 2002 5:00 AMNov 12, 2019 5:56 AM


Sign up for our email newsletter for the latest science news

When Justin Congdon was a teenager, he spenthis days in the woods of northeastern Pennsylvania, shooting pheasantsand trapping muskrats so he could sell their pelts for $4 apiece. Hewould have laughed had anyone told him he might spend the rest of hislife in a forest preserve trapping turtles, X-raying their bellies, andpainstakingly gluing their shells back together when they had the badluck to be hit by cars.

But that's precisely what he's doingon this late May afternoon at the University of Michigan's E. S. GeorgeReserve, as he has done every spring and summer for 27 years. Carryinga leather tool belt with a makeshift rectal thermometer, needle-nosepliers, and black Sharpie pen, he patrols East Marsh, an 11.5-acrehabitat with water lilies and wild irises. Most of the time he's on thelookout for female turtles— Blanding's, Common Snapping, and MidlandPainted— abundant with fertilized eggs and ready to unload them on thefirst warm day. A low plastic fence separates the turtles' marshlandhabitat from the higher, drier ground where they build their nests. For16 hours Congdon circles the marsh, following the fence that keeps theturtles from escaping. Any gravid— pregnant— female that wants to leavethe marsh must make a small contribution to science before she'spermitted to seek out a place to lay her eggs on the other side of thefence.

He spots a Midland Painted searching for a way pastthe barrier. She has the characteristic bright red trim around theedges of her shell and the intricate lined pattern, almost like a cavedrawing, underneath. He picks her up and pops his thermometer in hercloaca, the chamber in her tail where the digestive, urinary, andreproductive organs come together. She flails her legs wildly and voidswater onto Congdon's hands, but he gets his reading, a useful piece ofinformation for understanding how the turtle manages the heat it needsto carry out reproduction and other biological functions. With theSharpie, he marks her underside, or plastron, with body temperature,time, and location, tosses her into a camouflage-colored bag, andstrides quickly back to his turtle-processing shed, a former militaryradar outpost that has become the border patrol for wandering reptiles.

In this primitive two-room shed, Congdon has conducted some ofthe most sophisticated life-history studies of long-lived vertebrates—research that could upend our theories about how animals grow old andmight one day help unlock secrets of human longevity. For 49 yearsscientists have cataloged more than 12,000 turtles living on thereserve, compiling a huge database of individual reptiles. Each newcapture has its shell marked for identification, and all animals areweighed, measured, and inspected for disease or injury. Gravid femalesare X-rayed to determine how many eggs they're carrying and how bigthey are. Nests are tracked and locations recorded. During peak season,the shed sometimes looks like a turtle traffic jam, and processing cantake until 2 a.m.

Today's catch is a 16-year-old female that has been caught and X-rayedfive times since she first reproduced in 1996. Some of the turtles thatshow up at the shed are much older; although tagged as adults in the1950s, they are still healthy and fertile. They're also the key toCongdon's groundbreaking discovery: Blanding's and perhaps also MidlandPainted turtles don't senesce— deteriorate physically— as they growold. They simply don't age. And Congdon says the females actuallyproduce more eggs as they grow older: "They're crankin' compared to theyoung ones." When they do die, the cause is often an attack— hit by acar or mauled by a raccoon— or one of a number of infectious diseasesthat kill these turtles at all ages in seemingly equal proportions.While certain ailments, such as cancer and heart disease, strike olderhumans more often than they do younger ones, Congdon's animals don'tseem to become more vulnerable to disease as they grow older.

The findings are turning the discussion of aging in mammals upsidedown. "His work is a sharp challenge to a theory that has been taken atface value— that senescence is inevitable," says Caleb Finch, professorof biological sciences and gerontology at the University of SouthernCalifornia. "Here you have a vertebrate turtle that shows no increasein mortality and no loss of reproductive capacity at ages wheremammals, including humans, will shut down totally." Other species withlong life spans include sharks, tarantulas, and rockfish, and humangerontologists are starting to pay close attention. As Huber Warner,associate director of the Biology of Aging Program at the NationalInstitute of Aging, says, "If we knew what regulates life span inturtles, that might be useful in figuring out how humans age and how tointervene."

The first thing you notice about Justin Congdon,other than his deeply creased face and wild gray beard, is his passionfor telling one bravado-tinged story after another, preferably over acold Budweiser. Sit long enough and you'll hear about his adventure ona runaway logging truck while collecting lizard blood in the jungles ofMexico, an accident in which he almost lost a hand. Or he'll tell youabout his run-in with a particularly testy Banded Water Snake that hespotted one evening while walking along the fence at the Michiganreserve. The snake had been tagged by a graduate student, but "I hadn'tbrought a flashlight. So I grabbed the snake and flipped its head backand pulled the tail up to read the ID. I didn't see, because it wasgetting dark, that the snake had pulled its head free, and it bit me ina wide-open eye."

The impression he creates is that ofsomeone who lives far more happily outside polite society, someone whois simultaneously a meticulous biologist and a swashbuckling cowboy.Both images of himself seem to grow from the same impulse— the desireto dwell in unfettered wilderness, in places where people don't sipchampagne. "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 fashiondesigner was murdered. "Somebody came out on the news and said,'Tonight the world mourns for Versace.' Justin said, 'Can you believethat? The world mourns for the death of a guy who sews pants?'"

The two sides of Congdon's temperament— researcher and cowboy— fitnaturally together, but they didn't always. Growing up in a militaryfamily, he had almost no interest in his studies and couldn't wait tocome home from school to explore the swamps and woods near his house.Muskrats and water snakes held a fascination for him that classroomsand books did not. He assumed he would follow in his father's footstepsand pursue a career in the Navy, but three years of scrubbing toiletsand cleaning guns on an aircraft carrier persuaded him to try college.The thought of returning to school scared him so much that as he droveto Victorville, California, to enroll in a junior college, he keptsaying over and over to himself, "I hope I never get there."

Just one biology class convinced Congdon that he could make aliving pursuing his childhood fascinations. At 26, while working towarda master's degree in biology, he moved into an abandoned copper andsilver mine in the Mojave Desert, which he furnished with cast-offcarpeting and a propane refrigerator in order to study how kangaroorats and pocket mice use different desert habitats seasonally. For fourdays 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, hikingthe Providence and Granite Mountains; then he'd return to trap anotherquarter. At night he'd read by taillights salvaged from an abandonedcar and hooked up to the battery of his Volkswagen bus. "I hated goingnear civilization," he says. "I promised my parents that I'd call themevery time I went out for supplies, and I did. But there were two-weekperiods when they didn't hear from me."

In 1975 his mentor atthe University of Michigan, evolutionary ecologist and herpetologistDonald Tinkle, offered him a job on the E. S. George Reserve. The dayCongdon and his wife arrived, carting all their belongings with them,Tinkle announced he was flying off to Utah to work on another study. "Isaid, 'You've got to be kidding,'" Congdon recalls. "I thought, 'MyGod, 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 showedme the marking codes and where the equipment was, and then he left."

Once he had absorbed his new responsibilities, Congdon's days fellinto a pleasant routine, canoeing in the wetlands to collect data onthe residents. "I started trapping some marshes that hadn't beentrapped, and we had a 100-turtle day when I went into East Marsh forthe first time. At that point I think Don knew we were going to have agood study."

Tinkle died five years later, at 49. "I wasdevastated," Congdon says. "He was my mentor and academic hero." Justbefore his death, Tinkle called the National Science Foundation,announced he was terminally ill, and obtained permission for Congdon torun out the grant. The younger scientist vowed to oversee the projectin a way that would honor his predecessor. "I wanted it to be run asgood as it had been run, or better," he says. "I couldn't have had itany other way."

While crunching his data in the mid-1980s,Congdon made a startling discovery: The oldest female Blanding'sTurtles— more than 50 years old— had more egg clutches than youngerones, as well as more eggs per clutch. Not only that, they died at alower rate too. "What did I do wrong?" Congdon remembers thinking tohimself. "Did I make a mistake? Did I analyze it incorrectly?" He knewthat adult turtles kept growing throughout their lives, and so hewondered whether the true variable might be body size rather than age.Once he ran the numbers again, controlling for body size, he wasastonished to find that he got nearly identical results.

Atfirst, he didn't write up the findings. There was little or noconversation among gerontologists about nonhuman aging models. "I justcouldn't get anybody interested in what I was doing," he says. So heresolved 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 twodecades raising children, it behooves us to finish producing them whilewe're still young. Our genes favor early childbearing; they also ensurethat we'll be around long enough to raise our kids.

It alsobehooves creatures like mice and rats to have babies early in theirlives but for a different reason: If they don't, they might get eatenbefore they reproduce. "Even if a mouse was immortal as far asphysiological death, a predator would still get it within three or fouryears," says Whit Gibbons, an ecologist at the Savannah River EcologyLaboratory in Aiken, South Carolina, the facility where Congdon worksduring 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 10years, because there's no way those genes will be passed on."

And mice are among a group of short-lived animals, which includesworms, lizards, and fruit flies, that scientists have traditionallyused to study aging. With short-lived animals, "you can walk away froma project within three or four years, and you've got a lot of data, andyou can make a big impression on your colleagues," says RonaldNussbaum, a zoologist at the University of Michigan. Under suchpressures, 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 favoredthose individuals that were able to keep pumping out eggs.

With the Blanding's Turtles in particular, not only are the oldfemales still fertile, they're often more productive and have a highersurvival rate than their daughters and granddaughters. Congdon'stheory: Age brings wisdom, even in reptiles. "Blanding's Turtles know alot about the landscape that they live in," Congdon says. "I'm not justtalking about the immediate landscape. We have animals that travel fourkilometers [2 1/2 miles] to nest. Do they know where they are when theyare four kilometers away from where they started out? Yes. Did theyhave some innate, built-in map? No, they learned that route over yearsand years. So if a female goes to a place and it is not a successfulnesting site, the old ones know where to find the next-best placebetter than the young ones. When you make it to your sixties with nodoctors, you are the best of the best. Certainly, you can get run overby a mower. But maybe older females have a slight edge in avoidingrisk."

He knows this is hard for many people to believe."When you dissect a turtle's brain, you just go, 'Boy, there is not alot of room in there for a lot of thought.' I mean, they are tiny, tinybrains. But I think these turtles are way smarter than we give themcredit 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 learna lot."

While Congdon is developing life-history data onindividual captures, other researchers are trying to get a better graspon why the animals resist senescence. "The turtles are vertebrates, sothey'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 thatdamage human cells, they might have something to teach us."

James Christiansen, professor of biology at Drake University in DesMoines, is studying how telomeres, the simple, non-genetic DNAsequences that sheathe the ends of chromosomes, function in reptiles.Each time a healthy human cell divides, it loses a little bit of thetelomere, until the strands are too short to protect the chromosomes.At that point the DNA in a cell begins to break down, which triggerssenescence and death. Human cancer cells go off the program, producingan enzyme called telomerase that stops the shortening and renders themalignant cells immortal.

Turtles seem to follow a differentpattern. "Even though many species live in some of our most pollutedenvironments," Christiansen says, "they avoid cancer." Early results ofhis study suggest that some reptiles may receive a short burst oftelomerase early in life, which makes healthy cells rather thancancerous ones immortal. If this proves to be the case, he says, thehuman implications may be dazzling. "If we could do that with humansshortly after birth, before the mutations have a chance to creep in,"he says, "we could potentially add a hundred years to the human lifespan."

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 termsof not being able to go and go and go without paying. I smile when theold Blanding's ladies look at me, and I imagine them saying, 'OK, goahead, bother me today, but I'm going to outlive you.'" Congdon alsofears the turtles will outlive the Michigan study. He plans to returnto the reserve for five more summers— but will there be anyone to takeover 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 haveyet to be told, 'I want the work.' So I don't have anybody on thehorizon."

Today, though, he hasmore pressing concerns, like the fact that the late-spring chill seemsto 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, overthe East Marsh fence to build her nest, but he's concerned about thecloud cover and approaching cold. "She'll either commit really quick,or she won't," he says. "When the temperature goes down, all thebiological processes— strength, muscle coordination, ability to exportoxygen to the legs— go down." No. 5 makes her way up the side of an oldgravel pit, finds her spot, and starts digging, but then hits a rootand abandons the unfinished nest. She slowly inches farther up thehill, but the air has cooled noticeably. She gives up.

Back at the turtle shed, Congdon hears better news. Jason Sweas, hisundergraduate assistant from the University of Michigan, has witnessedthe first successful nesting of the season, on a lawn near the entrancegate. For an hour he watched as a Midlands Painted Turtle lowered herback end into the hole, laid her eggs, then spent an eternity coveringthem. 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 herefforts were almost invisible. When she was finished, Sweas capturedher and carried her to the shed.

He also brought a young malehe had spied lumbering around with his shell cracked after he was hitby a car. "The spine's not broken," Congdon notes, so he cuts afour-inch strip of black electrical tape, applies it to the brokencarapace, then spreads an adhesive over the tape. "The epoxy will holdit together until the bone grows back. Then it will fall off," heexplains. "My guess is that we'll see this guy, with a slightly damagedcarapace, years from now. I guess, technically, we shouldn't do thisstuff. But I don't think we've changed the demography in any measurableway. 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. Thesuccessful nester and the injured male will live in Congdon'sutility-room sink overnight and be returned to their swamp home in themorning. Before settling in for the evening, though, Congdon walks EastMarsh one last time. He releases No. 5, and she swims back into themarsh, presumably to lay her eggs another day. Congdon watches her asshe paddles through the water. Despite his insistence that he has noemotional attachment to his subjects, there's a look in his eyes thatconveys the gruff affection he has developed for the critters.

Verbally, though, he concedes nothing. "Another day," he says simply. "Another turtle."

A good starting spot for turtle information.

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!


Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Our List

Sign up for our weekly science updates.

To The Magazine

Save up to 40% off the cover price when you subscribe to Discover magazine.

Copyright © 2024 Kalmbach Media Co.