How do predator-induced changes affect prey vulnerability? Larvae of Chaoborus flavicans (Diptera: Chaoboridae) feeding on Daphnia pulex (Crustacea: Cladocera)

1. The relative food consumption and prey preferences of fourth-instar larvae of the phantom midge Chaoborus flavicans were investigated in laboratory experiments. Neonates and second instars of two clones of the cladoceran Daphnia pulex - an Arctic and an European clone - were offered to the predatory larvae. Each clone was divided into two groups: one group was exposed to the midge larvae during embryogenesis, whereas the other was not exposed to the predator. 2. While both exposed and unexposed neonates of the European clone had neck teeth, animals of the Arctic clone did not develop these spines. 3. A consistent rank order was observed in the vulnerability of the four prey types. Newborn daphnids from the Arctic clone were more vulnerable to predation than those from the European clone. Moreover, differences existed within each clone, regardless of neck teeth induction: Daphnia previously exposed to Chaoborus were less susceptible to the predators than unexposed prey. 4. The results show differences in the vulnerability of exposed and unexposed neonates that are not caused by the presence or absence of neck teeth. Perhaps the reduced vulnerability of exposed neonates was due to predator-avoidance behaviours.