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Of all the environmental pressures that all organisms across all kingdoms must face, one of the greatest is the risk of predation. The unpredictability of predation events from the perspective of a single individual is one of the major components of a changing, unstable environment (Gliwicz and Pijanowska, 1989; Lampert, 1987). The panoply of antipredator defenses among terrestrial and aquatic organisms involves a variety of morphological, behavioral, and life-history adaptations that even if they are not life-saving, may enable organisms to complete reproduction before predation occurs. Most of these phenotypic changes are directly induced by cues associated with the biotic agent, in the case of aquatic organisms, the chemical compounds (kairomones) released by a predator into the water. Herein we show that exposure of Daphnia to invertebrate and vertebrate kairomones results in changes in motion, behavior, and life history and at the molecular level involves changes in heat-shock proteins (HSPs) level and the actin and tubulin cytoskeleton. In addition, some of these effects are transgenerational, i.e., they are passed on from the mother to her offspring.

Diel changes in the depth distribution of Chaoborus flavicans larvae in thermally stratified aquaria with a distinct light gradient revealed that the larvae responded behaviorally to the presence of fish. Both the midday and midnight mean depths of the population were greater in the presence of fish. Most fish‐treated larvae found a daily refuge in bottom sediments. It appears that the stimulus for vertical migration is chemical, not visual or mechanical. The fish effect persisted for more than 15 d but was reversible. Those individuals that previously had been exposed to fish factor were considerably more sensitive to light than untreated larvae and showed a panic response when suddenly illuminated.

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