Diving into a lake next summer you could swallow hundreds of Daphnia pulex, a one-eyed, algae-sucking water flea. The creature has long captivated biologists with its ability to shift between asexual and sexual ways of life and survive for decades frozen at the bottom of a lake. But it is best known for its sensitivity to toxic chemicals, which helps ecologists monitor water quality in ponds and lakes. Now researchers have a chance to figure out how the water flea works, thanks to its newly sequenced genome, reported  online today in Science. One-third of the water flea's nearly 31,000 genes are unique and seem to respond to predation, exposure to toxicants, and bacteria. This has titillated geneticists and ecologists alike, who spy an opportunity to understand which genes are responsible for some of the animal's peculiar talents, such as growing protective tail spines, helmets, and neck teeth in response to the chemicals produced by predators. So when you gulp that mouthful of lake water, you can have the satisfaction of knowing that you have not only just swallowed a fully armored crustacean, but the first of its kind to have its genome sequenced.
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