Predator-Induced Phenotypic Variation in the Pattern of Growth and Reproduction in Daphnia hyalina (Crustacea: Cladocera)

1. The life-history patterns of the cladoceran Daphnia hyalina, widely distributed throughout northern temperate lakes, were observed to vary in the presence of different size-selective predators. 2. These changes were apparently initiated by waterborne cues released by predators. 3. In the presence of a cue released by predators preferring large adult D. hyalina, the daphnids reproduced at a smaller size and used a higher percentage of resources for reproduction than in the absence of this cue. The opposite was observed when daphnids were exposed to a cue originating from a predator preferring small juvenile D. hyalina. 4. The chemically induced responses in life-history traits took place within one generation of a single clone. 5. These results are in agreement with demographic theories concerning direct effects of size-selective predation on prey and are interpreted as adaptive responses to seasonal predators.