You might say that Charles Kerfoot, an ecologist at Michigan Technological University, can raise the dead. The crustacean eggs that Kerfoot reanimates in his laboratory technically have no perceptible metabolism, so by a strict physiologic definition, they are, essentially, not living. But Kerfoot manages to hatch living crustaceans from these eggs, some of whom have been dormant for an awfully long time.
The concept is simple: Microscopic crustaceans, such as water fleas and copepods, lay encysted eggs during tough times so their progeny can ride out droughts or other environmental perturbations. Sometimes these diapausing eggs last for decades, even centuries. Kerfoot and others studying resurrection ecology - a term he coined in a 1999 Limnology and Oceanography paper - find layers of increasingly older eggs buried in lake sediments, bring them back to life by subjecting them to favorable light and temperature cycles, and then study how the hatchlings compare to adults hatched from more recent eggs. In essence, they watch evolution in action. "You can actually interrogate the ancestors," Kerfoot says.
Resurrection ecology was born long before it acquired the moniker. Researchers in Europe have hatched eggs 15 to 40 years old since the 1960s. The practice became an experimental science in the 1980s, when Nelson Hairston, Jr., and a colleague at Cornell University systematically hatched 3-year-old copepod eggs collected from sediments at the bottom of two Rhode Island ponds and studied how reproduction timing in modern copepods differed from that in older populations.
Carla Caceres, who was Hairston's PhD student in the early 1990s, helped him drill cores deep into the mud at the bottom of Oneida Lake in New York to find and hatch increasingly older eggs. They incubated eggs in the laboratory while using chemical dating to verify the age of the surrounding sediments. "When we got the data back and found out that [the eggs] were centuries old," Caceres remembers, "it was pretty exciting." In a 1995 Ecology paper, Hairston and coauthors reported the successful hatching of 330-year-old eggs from one of the Rhode Island ponds. "None of us had realized quite how long they could live," Caceres says. The team was so excited that they even made t-shirts with "Eggs of the Living Dead" emblazoned across the back.
Caceres, now at the University of Illinois, uses resurrection ecology to study the invasion of crustaceans into artificial lakes left over from strip-mining scars. She has hatched decades-old eggs from microscopic crustaceans of the genus Daphnia, compared past populations to ones that dominate the lakes now, and charted how the species has changed. She has seen traits such as competitive ability, growth rates, and body size shift in successive generations of Daphnia as conditions in the lakes fluctuated.
Kerfoot and Larry Weider, an ecologic geneticist at the University of Oklahoma, recently linked pollution and changing predation rates in Portage Lake in Michigan to allelic shifts in a gene for a glucose digestion enzyme (Limnol Oceanogr, 49:1300-16, 2004). "[Resurrection ecology] can really be a powerful technique to look at how these populations have changed with environmental changes," he says.
In that paper, Kerfoot focused on how these Daphnia have adapted to changing predation rates in Portage Lake, a stone's throw from his Michigan Tech lab. Using the resurrected crustaceans, he's testing the "Red Queen's Hypothesis," which states, in part, that prey species are constantly changing to keep apace with their predators, as sort of an evolutionary arms race. (The term is derived from the Red Queen character in Lewis Carroll's "Through the Looking Glass," who told Alice: "It takes all the running you can do, to keep in the same place.") The diminutive crustaceans can cycle through 15 generations in an average year, so change is easy to spot. By reviving dormant eggs - some laid more than 75 years ago - Kerfoot has seen the species rapidly evolve morphologic defenses.
More recently, researchers reconstructed rapid evolutionary dynamics between Daphnia and one of its bacterial parasites by resurrecting individuals entombed in lake sediments (Nature, 450:870-3, 2007). "All of the sudden you have the timeframe to test conjectures regarding paleoecology at different sites," he says. "Evolution's taking place at a much faster rate than you would have thought."