Daphnia pulicaria hijacked by Vibrio cholerae: Altered swimming behaviour and predation risk implications

Parasites hijack hosts and alter the latters' behaviour so as to enhance their dispersion and transmission to new hosts and new environments. Daphnia, as one of the major zooplankton members in freshwater environments, are targets of parasitic fungi, bacteria, and even waterborne human pathogens. Although the effects of infestation on Daphnia have been studied for over 120 years, scarce information is available regarding behavioural consequences. Conspicuous swimming behaviour of Daphnia can increase predation rates by visual predators such as fish. Therefore, if the swimming behaviour of Daphniaare modified by infestation, their predation risk could increase. Here we observed the effect of Vibrio cholerae infestation on the swimming performances of Daphnia pulicaria in dark and light conditions to simulate the risk of detection by visual predators. Our results show that D. pulicariaboth with and without infestation by V. cholerae display similar swimming patterns in the dark. However, in light conditions, D. pulicaria infected by V. cholerae swim faster and travel more convoluted trajectories than those without infestation. Our study is the first to indicate that a microbial infestation can modify the swimming behaviour of D. pulicaria and that, consequently, infected D. pulicaria could experience more extensive predation by fish.