PLASTICITY OF DAPHNIA LIFE-HISTORIES IN RESPONSE TO CHEMICAL CUES FROM PREDATORS

The possible induction of life-history shifts in prey by chemicals released into the environment by potential predators was examined. Laboratory life-table experiments were conducted to examine the influence of chemical substances released from vertebrate (fish) and invertebrate (Notonectidae) predators on life-history features of two clones (B - coexists with fish, W - from a fishless pond) of the freshwater cladoceran crustacean, Daphnia magna. Significant differences between treatments in kev life-history features (i.e. size and age at first reproduction) were detected for each clone. Both clones showed a significantly smaller size at first reproduction when raised under fish-treated water, when compared with animals raised under invertebrate-treated water. Control values were intermediate. A significant decrease in age at first reproduction was observed for clone W when raised under the fish treatment, when compared with the invertebrate treatment. No significant differences were observed in age at first reproduction for clone B. These data indicate that genetic (clonal) variation in the magnitude of response to chemicals released by potential predators, exists in Daphnia for a number of life-history traits. Data are discussed in reference to the adaptive value of such life-history plasticity.