PREDATOR-INDUCED PHENOTYPIC PLASTICITY IN DAPHNIA-PULEX - LIFE-HISTORY AND MORPHOLOGICAL RESPONSES TO NOTONECTA AND CHAOBORUS

Results from a laboratory life-table study show Daphnia pulex has a unique set of rapidly induced responses to waterborne chemicals from each of two predator species. Additionally, Daphnia exhibits a unique set of induced responses when simultaneously exposed to both predators. Daphnids possessed neck teeth and experienced delayed maturity when exposed to waterborne chemicals released from larvae of the phantom midge Chaoborus americanus. Possessing the Chaoborus-induced phenotypic plasticity was not associated with a lower population growth rate relative to that in the control treatment. When exposed to waterborne chemicals released from the backswimmer Notonecta undulata, D. pulex exhibited an unexpected assemblage of responses. The Notonecta-induced phenotypic plasticity included rapid juvenile growth to a large size at first reproduction, little growth beyond maturity, and high reproductive output. Simultaneous exposure to chemical cues from Notonecta and Chaoborus resulted in a life history and morphologies that agreed with predicted life history and morphological responses of Daphnia that had been simultaneously exposed to large- and small-size selective predators.