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The discovery, reported in the Sept. 30 issue of the journal Nature, shows that environmental degradation can be reduced when the affected animals evolve quickly, according to Cornell biologist Nelson G. Hairston Jr.
"It appears that ecological events that we think of as occurring relatively quickly -- such as nutrient enrichment of a lake -- can be influenced by the rapid evolution of the animals that are affected," says Hairston, a professor of environmental science. "If these little crustaceans hadn't changed with the times, their kind might not have survived." Hairston co-authored the Nature report with Winfried Lampert, director of the Max Planck Institute for Limnology in Plön, Germany.
In less than 30 years, as Germany's Lake Constance suffered environmental degradation from phosphorus pollution, populations of tiny crustaceans called Daphnia found more and more toxic cyanobacteria (also called "blue-green algae") mixed with their favorite food, a more edible type of algae. So the crustaceans adapted to handle a less nutritious food that would have seriously stunted the growth of their ancestors, and they became one of the important, natural controls for toxic cyanobacteria in the lake.
The research, carried out at the Germany institute, documented the crustaceans' express-style evolution by hatching a series of dormant Daphnia eggs that were found, level by level, in lake-bottom sediments in a state of "diapause." Diapausing animals, such as certain insects and crustaceans, can suspend their growth and development for years or even centuries during periods of unfavorable conditions.
In Hairston's Cornell laboratory, researchers already had learned how to awaken 300-year-old crustacean eggs. Working at Lake Constance, the biologists needed to go back only 37 years, beginning with Daphnia eggs that were deposited on the lake bottom in 1962, to trace the clever crustaceans' evolution. They hatched Daphnia eggs that piled up year after year in sediments, then reared the crustaceans to adulthood in the laboratory and offered them cyanobacteria from the lake. Cyanobacteria produce high concentrations of the hepatotoxin, microcystin-LR.
Daphnia with 1960s genes -- before Lake Constance became so polluted and cyanobacteria were so plentiful -- couldn't stomach the modern meal. But by the late 1970s -- just a decade later -- Daphnia had become much more adept at living on a diet laced with the toxic algae. And Daphnia hatched from eggs deposited between the 1980s and the 1990s were found to retain this ability.
DNA tests of Daphnia grown from eggs that were deposited over the years revealed that crustaceans that couldn't cope easily with cyanobacteria were virtually eliminated from the population; all that remain today are cyanobacteria eaters, even though the toxic bacteria still aren't particularly nutritious.
"Strong natural selection can lead to rapid changes in organisms, which can, in turn, influence ecosystem processes," the biologists concluded in their article.
Other authors of the Nature report, titled "Dormant eggs record rapid evolution," are Lawrence J. Weider, Max Planck Institute for Limnology; Ursula Gaedke, Limnology Institute, Universiy of Constance; Cami L. Holtmeier, David M. Post and Jennifer A. Fox, graduate students in ecology and evolutionary biology at Cornell; Janet M. Fischer, postdoctoral fellow at Cornell; and Carla E. Caceres, a former graduate student in Hairston's laboratory and now a biologist at the Illinois Natural History Survey's Center for Aquatic Ecology. At Cornell, Hairston (pronounced "HAHRS-ton") is the Frank H.T. Rhodes Professor of Environmental Science.
The Lake Constance study was funded by grants from the U.S. National Science Foundation and the German Academic Exchange Service.
Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.
-- Cornell Ecology/Hairston Lab: http://www.es.cornell.ed u/hairston/hairston.html
-- Max-Planck-Institut für Limnologie: http://www.mpil-ploen.mpg.de/
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