April 27, 2012

Do Prey Fear Unfamiliar Predators?: Physiological Responses of Daphnia to Native and Invasive Predators

Jessica Churchill, Advisor: Leif Hembre

Studies examining the impact of non-indigenous species often focus on food web or ecosystem effects of the invader. However, few studies have investigated how individual native populations respond to the presence of a non-indigenous species. This study employs a heart rate (HR) bioassay to assess whether native prey (Daphnia) exhibit an increase in HR (a fright response) after exposure to kairomones from the spiny water flea (Bythotrephes longimanus), an invasive zooplankton predator. HR responses of Daphnia from three lakes that differ in predator composition were assayed after exposure to kairomones of three predators (Bythotrephes, fish, and Chaoborus). Island Lake has been invaded by B. longimanus and also contains fish and Chaoborus. The other two lakes have not been invaded by B. longimanus; Lake Itasca contains fish and Chaoborus while Arco Lake is a fishless lake. Additional assays were performed to determine if ontogenetic stage or species had an effect on Daphnia HR response. Daphnia from the invaded lake exhibited an elevated HR after exposure to all three predator kairomones. Daphnia from the uninvaded lakes showed no change in HR when exposed to the invader’s kairomones. This suggests that Daphnia in the invaded lake have adapted to recognize the presence of B. longimanus, while Daphnia from the uninvaded lakes are naïve to this unfamiliar predator. The effects of ontogenetic stage were insignificant, while species had a marginal effect on HR response.