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 un ique set of rapidly induced responses to waterborne chemicals from eac h of two predator species. Additionally, Daphnia exhibits a unique set of induced responses when simultaneously exposed to both predators. D aphnids possessed neck teeth and experienced delayed maturity when exp osed to waterborne chemicals released from larvae of the phantom midge Chaoborus americanus. Possessing the Chaoborus-induced phenotypic pla sticity was not associated with a lower population growth rate relativ e to that in the control treatment. When exposed to waterborne chemica ls released from the backswimmer Notonecta undulata, D. pulex exhibite d an unexpected assemblage of responses. The Notonecta-induced phenoty pic plasticity included rapid juvenile growth to a large size at first reproduction, little growth beyond maturity, and high reproductive ou tput. Simultaneous exposure to chemical cues from Notonecta and Chaobo rus resulted in a life history and morphologies that agreed with predi cted life history and morphological responses of Daphnia that had been simultaneously exposed to large- and small-size selective predators.