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Escape Predators, Get Parasites

A particular predator defense used by water fleas makes them more susceptible to parasite infections, new research shows.

Jef Akst
Jef Akst

Jef Akst is managing editor of The Scientist, where she started as an intern in 2009 after receiving a master’s degree from Indiana University in April 2009 studying the mating behavior of seahorses.

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WIKIMEDIA COMMONS, PAUL HEBERT

A common belief among ecologists is that, in a way, predators help their prey by removing the weak and sick from the population and reducing the chance of disease spread. But that idea, known as the "healthy herds hypothesis," has been challenged by recent data, published in Functional Ecology, suggesting that some water fleas (Daphnia dentifera) are better at defending themselves against predators but are at great risk of parasitic infections. When Daphnia sense certain distinct chemicals exuded by their predators, they grow larger, making it more difficult for the predators to eat them. But larger Daphnia, it turns out, also consume greater quantities of a deadly yeast parasite, known as Metschnikowia. Furthermore, once inside a larger Daphnia, the parasite appears to release more spores, which go on to infect other water fleas.

“While some have argued for increasing predator...

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