Scientist Urges Dormant Eggs to Life to Test Evolution
'Resurrection Ecology' Is a Whole New Field
April 14, 2005
Scientists are bringing the past to life by hatching eggs once thought to be dead and producing colonies of animals as they existed decades ago.
They are calling it "resurrection ecology," and it's a whole new field that quite literally allows scientists to observe evolution as it occurred, using animals that were quite different than their kinfolk today.
And who do they have to think for it all? Alice in Wonderland.
Alice, as we all know, had a pretty difficult life in Lewis Carroll's yarn. In one scene she complained to the queen that she didn't seem to be getting anywhere even though she was running as hard as she could.
She was admonished that resting on her laurels was not an option. "It takes all the running you can do, to keep in the same place," the queen told her.
Change or Die
In 1973, biologist Leigh Van Valen of the University of Chicago picked up on that theme and postulated that in nature, it's not enough to tread water. One must constantly evolve to keep abreast, or ahead, of predators.
That became known as the Red Queen Hypothesis, suggesting that change is not only good, it's essential because without it, organisms will perish. You've got to stay ahead of the competition.
For decades now, scientists have tried to either prove, or disprove, Valen's argument. And now, at least one group thinks it has succeeded.
"We are confirming the Red Queen Hypothesis," says biologist W. Charles Kerfoot of Michigan Technological University, who has spent years now chasing Alice to see if she really did have to keep running just to stay in place. He is one of several authors who took over a recent issue of the journal Limnology and Oceanography, reporting widespread results in the search for "resting eggs" that are dormant, but still alive.
Kerfoot found his answer in the murky waters beneath an inland lake on Michigan's Upper Peninsula. Portage Lake has gone through many changes over the past century. Copper mines flooded the lake with debris. Dredging changed its nature considerably. And more recently, the waters have been depleted of oxygen through the growth of algae, a process called eutrophication.
Kerfoot began collecting cores from the sediments beneath the lake a few years ago because of something he had learned in Germany. He had been invited there, along with several other researchers, by the Max-Planck Institute to study lakes that had not recovered fully from pollution, even though the quality of the water had been restored.
Dredging Ancient Eggs
Of particular concern was the absence of plankton, those tiny animals that are at the bottom of the food chain and so critical to so many other organisms. It was while combing through sediments from that lake that Kerfoot and his colleagues made a remarkable discovery.
They found that eggs that had been trapped beneath the sediment years ago had never hatched, but miraculously, were still alive.
A little incubation and bingo, the eggs hatched into animals not as they appear today, but long ago when the eggs were first deposited on the floor of the lake. How they survived all that time is a great mystery.
"My friends in genetics would really like to know how in blazes they did that," Kerfoot says.
Biologist Nelson Hairston, a member of the Max-Planck team, was among the first to describe the finding several years ago.
After returning to the States, Kerfoot turned his attention to Portage Lake. The history of the lake had been so well documented that he knew it would be possible to come up with precise dates for whatever he might find there.
Kerfoot and geneticist Lawrence J. Weider, formerly of Max-Planck and now of the University of Oklahoma, found layers of eggs dating back nearly a century that were clearly alive. These aren't man-eating dinosaurs, but they were living specimens from a time that is now past.
The eggs had been deposited by a tiny shrimp-like animal in the zooplankton family known as Daphnia retrocurva. These critters live in the cool waters of the lake for only one summer, and then die out, leaving their eggs behind to begin the process anew the next spring.
Bigger Helmet Heads Dissuade Predators
The scientists exposed the eggs to sunlight and warmth, about what they would expect in the spring, and the eggs hatched. As they grew to maturity in tightly controlled experiments, they changed over the years, particularly in the length of their spines and the size of their helmets.
By examining the fossil record, the researchers found that fish that prey on the small animals also changed significantly over the years, at least in terms of abundance.
About 80 years ago, when the predators were all over the place, the Daphnia retrocurva extended the size of its helmet and spines to make itself less appetizing. Later, when the number of predators shrank, the animal reduced the size of those features, thus conserving its energy for other uses.
The researchers had hit pay dirt. The changes in Daphnia retrocurva were precisely what would have been expected as part of the predator-prey interaction.
Furthermore, DNA analysis shows that the changes were passed on genetically from one generation to the next, until they were no longer needed, thus confirming that the researchers had caught evolution in the act.
Lee Dye's column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.