WOODS HOLE, Mass. — In case you were wondering, Kristin Gribble is not a basher of fruit flies or roundworms. She wants to be clear: She bears no ill will toward those invertebrates so often studied that they’ve become scientific celebrities, recognizable by their truncated Latin names. She knows that Drosophila and C. elegans are powerful tools. She understands the allure of experimenting on creatures we know better than we know ourselves.
As an ecologist, she also thinks we might come to know ourselves a little better — and perhaps, stave off certain indignities of old age — by scrutinizing less famous spineless creatures in the lab. She’s staked her career on a particularly obscure one, and hopes others might do the same. Three to five times a year, she makes a point of mingling with the telomere-researchers and cell-rejuvenators and longevity-hounds who populate scientific conferences on aging. Like everyone else, she’s there to give papers and exchange ideas. But she’s also on a mission: to preach the gospel of rotifers.
“I feel like a bit of an evangelist,” said Gribble, a researcher at the Marine Biological Laboratory on Cape Cod. The good news she spreads is that there’s a creature with a genetic makeup, a lifespan, and a sexual bent that make it a good candidate for certain studies on how older bodies fall apart — and how we might hold them together. There’s a catch, though: “I do have to spend a portion of my talk every time explaining what the heck a rotifer is.”
Chances are you’ve swum with one or swallowed one or stepped on one or all of the above. They’re tiny animals, some microscopic, some the size of a speck of dust. And they’re everywhere: in the acidic water collected by the former pyrite pit-mines of Poland’s Sudety Mountains and in the salty “soda lakes” of Kenya’s rift valleys, in the fjord-like lochs of Scotland and in the smelliest of America’s sewage lagoons.
No matter how fleeting a body of water is, rotifers can live in it. A moisture bauble caught ornament-like between strands of moss or lichen is enough. In case their pond or droplet dries up, they’ve evolved a neat stunt to withstand desiccation, forming hard little eggs that can last a decade, blowing about with wind gusts and traveling on birds’ feet. Terry Snell, an emeritus professor at Georgia Tech, has even seen some of them survive an hour of near-boiling.
That isn’t the creatures’ only trick. Rotifers from one lineage never have sex, cloning themselves instead, and refreshing their genes by importing DNA bits from bacteria, fungi, and plants. The species Gribble studies is asexual — females cloning females cloning females — until the going gets rough, when the mother resorts to making males.
“The male is very different than in a human. The male rotifer does nothing but try to impregnate a female. He doesn’t have a mouth or a stomach. It reduces maleness to its essential parts,” joked Julia Kubanek, a chemistry professor who works with Snell at Georgia Tech.
If that doesn’t sound entirely like the biology of the humans you know, you would not be wrong. Then again, in some ways, certain underwater creatures are more like us than the standard organisms of the lab — and Gribble was just coming into her own as a scientist when that was coming to light.
She’d grown up in the dairy cow country around Arena, Wis. — not as much of a farm kid as some of her classmates, but still someone whose parents had 40 to 50 head. Her after-school routine involved scrubbing the bulk tank to keep bacteria from colonizing the fresh milk. She imagined she’d become a nurse or a teacher. “That’s all I knew girls did when I grew up,” she said. “I didn’t even know there was a thing they called grad school.”
Her own conversion began with a vision of phytoplankton, glimpsed in an undergraduate class on aquatic ecology — and within a few years she found herself sieving out toxic dinoflagellates she’d hauled up from the Gulf of Maine.
By the turn of the millennium, she knew what grad school was and after six years of waitressing, hotel housekeeping, and research assisting, knew she had to go. It was right around the time that the first genomes were being sequenced — and there were some pretty notable differences between our favorite lab animals’ and our own. We might have a dozen versions of one sort of gene, while Drosophila and C. elegans would have only a handful. “You think something that must make mammals or humans special is that they have more copies of these genes,” explained Mansi Srivastava, an evolutionary biologist at Harvard. “But then a big surprise came when we started sequencing all these other species.”
The starlet sea anemone, for instance — a tentacled denizen of the salt marsh — turned out to have about as many of a specific subset of genes as humans did. It happened again and again: Sometime in the last 600 million years or so, the ancestors of today’s fruit flies and worms had shed some of the genetic bits that humans and jelly-like sea creatures still share.
That didn’t escape the notice of administrators at the National Institutes of Health. “If you don’t need those genes, you lose them,” said Felipe Sierra, director of the division of aging biology at the National Institute on Aging. He hadn’t realized such gene loss occurred until after he accepted the position in 2006. “I was with my antennas open even more than usual, because I was starting my new job,” he remembered.
As he asked around about organisms, beyond flies, worms, and mice, that might help us understand the biology of aging, a whole menagerie has come out of the woodwork. He heard about bats that can survive a storm of human-killing pathogens and naked mole-rats that live decades longer than their fur-covered cousins. He heard about clams that gurgle on the seafloor for 500 years; you can read the passage of time in the lines on their shells, as if they were rings on a tree.
Eventually, he also heard about rotifers. They were different from those bats, rats, and quahogs: What attracted researchers like Gribble was not how long rotifers lived but how quickly they died. After all, if you want to test whether a drug or a diet extends lifespan, and the creature you’re working on hangs around for years and years, the experiment could outlast the experimenter. The risk is remote with rotifers: When not in desiccation survival mode, their life cycle lasts only a few weeks.
Gribble is hardly doing this work from scratch: We’ve been peering at rotifers through microscopes since Antonie van Leeuwenhoek first noted, early in the 18th century, that their cilia — the hair-like appendages they whirl through the water to find sustenance — reminded him of wheels, an image that gave them their name. Biologists the world over still work on them. To aquaculture experts, they’re larval fish food; to environmental scientists, they’re bellwethers at the bottom of the pond. That means their life histories have been pored over, their reproductive habits prodded.
Gribble uses that to her advantage. If she wants a population of identical rotifers, so that she knows different outcomes in her experiments aren’t because of innate differences, she simply lets them reproduce clonally, like some science-fiction dream. But if she wants to introduce variation in their genes, she can tweak their environment, nudging them toward making males and having sex. “We can have it both ways, which is sort of nice,” she said.
They’re not without their challenges, either. “There’s a real push in the aging community to not only think about extension of lifespan, but to think about extension of healthy lifespan, the health span,” Gribble explained. “But with rotifers, we can’t ask them how they’re feeling.”
Instead, her team videotapes and measures how they twitch and flick and swim. Especially useful is the rotifers’ propensity to gravitate toward light: “One of the research assistants in the lab, she calls it the zombie swim. No matter what they’re doing, they make a beeline toward that light source,” Gribble said. That inclination, it turns out, wanes with age.
Using those kinds of behavior, Gribble and many others have started to untangle the wires that might be driving such late-life changes. As Snell put it, “She’s now on the forefront, she’s probably the leading rotifer aging researcher in the world.” Meanwhile, she emphasizes how many other scientists there are in her “rotifer family.” Their findings are incremental: That certain drugs can help maintain their ability to swim toward the light. That under certain conditions, reducing the calories of their algal diets might extend their lives.
No matter how many genes a creature might share with us, the usual caveats of animal research apply. Before they might come anywhere close to helping humans, whatever observations occur among the rotifers will have to move up the evolutionary tree, into other invertebrates and then rodents and then larger mammals.
Gribble’s proselytizing has met with some skepticism from hardliners in the worm and fly and yeast camps — but she has managed to reel a few researchers in.
About five years ago, Karl Rodriguez, of the University of Texas Health Science Center at San Antonio, got to talking with her at an aging conference held on a dude ranch. He was a naked mole-rat and C. elegans man, studying how the cellular cleanup crews change with age — and he was intrigued to see those patterns replicated in Gribble’s rotifers. He wanted to know more, so she shipped him some.
They arrived by the thousands, frozen in vials, kept cold by Styrofoam. “You basically get test tubes, we add buffer and crush ‘em up, and that releases all the proteins,” he explained. Then he started measuring the levels of different molecules.
He’d tried to do the same with C. elegans, but had run into trouble with the worm’s rigid outer envelope. The force needed to break through it also tore apart the compounds he was trying to study. Not so with the creatures from Gribble’s lab: “Rotifers, they’re squishier, they’re easier to work with.”