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."