Daphnia Host Clones (IMAGE) PLOS Caption Exposing Daphnia host clones to spores from the castrating bacterium Pasteuria ramosa provides experimental evidence that parasite fitness is maximized at intermediate levels of virulence. Credit Jensen et al Usage Restrictions Must cite PLoS Biology License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.