When battling a deadly parasite epidemic, 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.
A new study reveals that the number of vertebrate predators in the water and the amount of food available for Daphnia to eat influence the size of the epidemics and how these "water fleas" evolve during epidemics to survive.
The journal Science published the results in this week's issue. The National Science Foundation (NSF) and the James S. McDonnell Foundation supported the research.
"This study is a great example of why the most obvious response to disease, increased resistance, may not be the best solution," says Saran Twombly, program director in NSF's Division of Environmental Biology.
"When populations are stressed by other factors such as food or predators, remaining susceptible to a disease is the best route to long-term success."
The study shows lakes with high nutrient concentrations and lower predation levels exhibit large epidemics, and the yeast in the water, Metschnikowia bicuspidata, has less effect on Daphnia as the Daphnia become more resistant to infection.
However, in lakes with fewer resources and high predation, epidemics remain small and Daphnia evolve increased susceptibility to the parasite.
"It's counterintuitive to think that hosts would ever evolve greater susceptibility to virulent parasites during an epidemic, but we found that ecological factors determine whether it is better for them to evolve enhanced resistance or susceptibility to infection," said the paper's lead author Megh
|Contact: Cheryl Dybas|
National Science Foundation