Scientist Urges Dormant Eggs to Life to Test Evolution

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 A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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