Weakness Can Be an Advantage in Surviving Deadly Parasites, a New Study Shows

http://www.sciencedaily.com/releases/2012/03/120329141914.htm

ScienceDaily (Mar. 29, 2012) — When battling an epidemic of a deadly parasite, less resistance can sometimes be better than more, a new study suggests.

A freshwater zooplankton species known as Daphnia dentifera endures periodic epidemics of a virulent yeast parasite that can infect more than 60 percent of the Daphnia population. During these epidemics, the Daphnia population evolves quickly, balancing infection resistance and reproduction.

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The study shows that lakes with high nutrient concentrations and lower predation levels exhibit large epidemics and Daphnia that become more resistant to infection by the yeast Metschnikowia bicuspidata. However, in lakes with fewer resources and high predation, epidemics remain small and Daphnia evolve increased susceptibility to the parasite.

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