Sci. Aging Knowl. Environ., 11 May 2005
Death in the Dirt
Long-lived in the petri dish, mutant worms bite the dust in soil
Lab life is sweet for the average nematode, but it's particularly congenial for some mutant worms. Luxuriating on a comfy bed of agar and feasting on bacteria, the creatures can survive more than twice as long as nonmutants. But new work suggests that the altered worms falter in the wild. Mutants that live unusually long in the lab die abruptly when raised in soil. The findings add to the evidence that organisms can't get extra time for free.
Alterations in several genes stretch worm life span in the petri dish. For example, glitches in the daf-2 gene can double longevity (see Johnson Review). The worms also resist stresses such as high temperatures that shrivel ordinary nematodes. Although they seem like �ber-worms, evolutionary theory suggests that the mutants carry other flaws that limit their fertility or subvert their health. Otherwise, the critters would gain extra time for reproduction and swamp their counterparts, becoming the prevalent form (see "Get Wild"). Some experiments support this view. For example, a 2004 study by molecular geneticist Gordon Lithgow of the Buck Institute for Age Research in Novato, California, and colleagues revealed that normal worms trump daf-2 mutants in the culture dish (see "Paying the Price"). But researchers don't know how long the animals live in the wild.
Physiologist Wayne Van Voorhies of New Mexico State University in Las Cruces and colleagues added lab worms to soil collected from Madison, Wisconsin, and measured their survival. Scientists have previously dug up wild nematodes nearby, so the researchers expected the dirt to be hospitable to the creatures. "I was shocked" at how quickly the nematodes died, says Van Voorhies. Nonmutant worms that endure for about 12 days on agar lasted for only 1.5 days in soil. And daf-2 mutants that exist for nearly 4 weeks in the petri dish perished after less than a day in the soil. Suspecting that organisms in the dirt might be killing the worms, the researchers repeated the experiment in sterile soil but obtained similar results. "The daf-2 mutants are not as robust as wild-type" worms, at least when they face the trials of a dirty existence, says Van Voorhies. The scientists fed the worms amply, and their cause of death remains mysterious, he says.
"This is the second torpedo that daf-2 [mutant superiority] has taken in the last several months," says Lithgow, referring to his group's 2004 paper. "Although these animals appear healthy, they are sick in some environments." Studies like Van Voorhies's are important, he adds, because they "get people thinking about what these genes are really doing." The paper helps "connect lab results with the real world," says demographer James Carey of the University of California, Davis. "It gives us an important frame of reference." However, Carey questions whether dirt is really the creatures' native habitat. The wrigglers can be extremely hard to find underground, even with plenty of spadework, he says. The worms might die because they pine for different surroundings, Carey says. Further work might reveal why dirt doesn't agree with them.
May 11, 2005
Science of Aging Knowledge Environment. ISSN 1539-6150