Predator-induced morphological defenses of marine zooplankton

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Intellectual Merit -- Predator-induced changes in the defensive structures of prey occur in diverse organisms and habitats. Curiously, a search of reference data bases reveals no reports of such changes for marine zooplankton. In contrast, reports of predator-induced morphological changes are numerous for freshwater zooplankton, benthic marine animals, and phytoplankton. Experiments in the PI's lab have demonstrated that predators induce changes in shells of the planktonic veligers, that caged predators induce the change without direct contact, and that this prior exposure to a predator subsequently decreases vulnerability of the veligers. This research extends these studies to diverse kinds of marine planktonic animals. The study concentrates on four prey-predator interactions: gastropod veligers as prey with crab zoeas as predators; echinoid plutei, crab zoeas, and copepod nauplii and copepodids as prey with fish as predators. For each prey-predator combination, the hypotheses to be tested are (1) presumed defensive structures develop differently in response to stimuli from predators, injured conspecific prey, and (2) prior exposure to predators reduces vulnerability. If these results are positive, two other hypotheses will be tested. (3) The reduced vulnerability following exposure to predators involves the induced defensive morphology (as indicated by direct observations of predators' attacks and handling of predator-exposed and predatornaive prey and the escapes by prey). (4) Exposure that induces changes in prey morphology results in slower prey growth. If results for hypothesis 1 are negative for a prey species, additional kinds of prey and predators will be tested. Induced morphological defenses convey information about predator-prey interactions in the field, variation in predation risk, processes that reduce mortality and reduce variation in mortality, what features are effective defenses against predators, and trade-offs for defenses. Also, if induced defenses are common, ignoring the defenses and their trade-offs will result in incorrectly designed laboratory experiments and misinterpretation of data. Alternatively, if predator-induced defenses prove to be rare among marine planktonic animals, then the risks for marine zooplankton and the costs and benefits of defenses differ from those for freshwater zooplankton.Broader Impacts -- The project includes a graduate student's dissertation research and supports research by undergraduates. The research will involve an undergraduate supported by a Blinks Fellowship, in a program at the Friday Harbor Laboratories (FHL) that is designed to bring students in underrepresented minorities into research in the marine sciences. Mentoring of undergraduate research jointly with the PI will enhance the graduate student's experience as a teacher. The PI and students will also present results in the lectures and open houses at FHL for the general public and at national and international meetings. The PI will incorporate result and new questions from this research into courses in larval ecology. Students from many institutions nationally and internationally take this course at FHL. The frequency or scarcity of morphological induced defenses will raise further questions about the specificity of stimuli and effectiveness of responses in marine zooplankton, which live in the largest habitat on earth, encounter diverse kinds of predators, and provide informative contrasts with freshwater zooplankton.