When predaceous foes meet their match: Predator-induced defenses in marine planktonic larvae

Many organisms inhabit unpredictable environments. The difficult adaptive challenges facing these organisms are met in a variety of ways. For some, environmental uncertainty favors flexibility in phenotypic traits allowing fine-tuning of the phenotype to better match present conditions. Inducible defenses are phenotypically plastic traits that alter the interactions between predators and prey. Induced defensive responses are well-documented in varied habitats to a diversity of predators and throughout ontogeny and include alterations in behavior, life histories and morphologies.;Despite the pervasiveness of predator-induced defenses exhibited by diverse plants and animals in both terrestrial and aquatic environments, there are few reports of predator-induced defensive morphologies and shifts in life histories in marine zooplankton, including the planktonic larvae of marine organisms. Rarity of these types of responses in marine zooplankton would imply a difference in predation risk compared to those experienced by freshwater zooplankton and benthic marine adults, whereas the presence of such plasticity in defenses would imply that risks are modified by developmental responses.;In this dissertation I report predator-induced morphological change and life history shifts in the planktonic larvae of diverse marine organisms, representing three clades of Metazoans. Specifically, stimuli from predators induced a more protective shell morphology in larval gastropods (Lophotrochozoans), asexual reproduction (cloning) and reduced size in larval sand dollars (Deuterostomes), and accelerated development in larval crabs (Ecdysozoans). Taken together, these data demonstrate that plasticity of defensive responses occurs in phylogenetically distinct marine zooplankton and suggest that developmental responses of marine zooplankton to predators may be common.