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Daphnia evolve into pollution eaters


A Daphnia crustacean swims in a sea of toxic blue-green algae.  

October 1, 1999
Web posted at: 11:23 a.m. EDT (1523 GMT)

A crustacean in Germany's Lake Constance has evolved quickly to allow it to consume toxic forms of its main food source. Crustaceans that have adapted to increasing levels of pollution in a German lake over the last 30 years are controlling the growth of toxic blue-green algae, researchers reported in Thursday's issue of the journal Nature.

"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," Nelson Hairston, a biologist at Cornell University, said in a statement.

Germany's Lake Constance has suffered environmental degradation from phosphorus pollution over the last 30 years. As a result, tiny crustaceans, called Daphnia, found more and more toxic cynobacteria known as blue-green algae mixed in with the non-toxic algae that composed their main diet.

The crustaceans adapted to the less nutritious diet, which not only ensured their survival, but has also served as a natural control for the cynobacteria in the lake, said Hairston.

Hairston and colleague Winfried Lampert, director of the Max Planck Institute for Limnology in Plon, Germany, documented the crustacean's rapid 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. Since Hairston already knew how to awaken 300-year-old crustacean eggs, it was easy for him to go back 37 years and trace the crustacean's evolution.

The researchers reared the crustaceans to adulthood in the laboratory and offered them cynobacteria from the lake. Daphnia with 1960s genes before the lake was polluted could not eat the cynobacteria. However, Daphnia from the late 1970s forward could survive on a diet laced with the toxic algae.

DNA tests further showed that Daphnia evolved from a species that could not cope with the toxic bacteria to a species that could. "Strong natural selection can lead to rapid changes in organisms, which can, in turn, influence ecosystem processes," the biologists confirm in the Nature article.

Copyright 1999, Environmental News Network, All Rights Reserved

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Nelson Hairston
Max Planck Institute for Limnology
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