Water flea close-up

Who knew? The humble water flea has 31,000 genes that can do remarkable things. Credit: Christian Autotte

Sharon Oosthoek

A tiny water flea possessing more genes than you or I has the potential to be a highly sensitive and inexpensive pollution detector, say scientists who recently sequenced its genome.

A single Daphnia pulex – a crustacean found in freshwater habitats in Ontario and around the world – contains nearly 31,000 genes, compared with our 23,000. Until a group of international researchers, including University of Guelph evolutionary biologist Teresa Crease, began working on the water flea’s genome, many of those genes had not previously been seen.

Scientists already knew that the water flea reacts to chemical signals from predatory fish by growing protective “teeth” on its neck and spines on its tail. But in a paper published in the journal Science in February, Crease and her colleagues say many of the flea’s newly described genes turn on or off in reaction to toxins in the water, thereby allowing the flea to tolerate pollution.

“Eventually, we will be able to monitor populations of Daphnia to look for changes in levels of gene expression before the levels of the pollutants get to the point where we might notice them,” says Crease.

Because a water flea can reproduce through cloning, making its offspring genetically identical, scientists can put a creature with the same genes in two different environments – one that is contaminated with a specific toxin, and one that is not. By figuring out the difference in the way the flea’s genes are expressed in contaminated water, they can then monitor for specific pollutants.

“We can use the organisms to ring the bell, to warn us that something is in the water so we can go look for the source,” says Crease.

Project leader John Colbourne, director of Indiana University’s Center for Genomics and Bioinformatics, says that this early warning system is significant, given that there are roughly 80,000 human-made chemicals in the environment, but only seven to 10 percent have ever been tested for their potential toxicity.

“Another 2,000 chemicals are brought to market every year,” he adds. “We need to find some method to help determine what’s good and what’s bad in our environment.”