DAPHNIA BEHAVIOR AS A BIOASSAY OF FISH PRESENCE OR PREDATION

1. Fish cues are associated with changes in Daphnia behaviour, however , the causes of these responses are generally unknown. 2. Two kinds of experiments were done in order to test whether the predator cue induc ing changes in Daphnia galeata mendotae was: in solution and molecular ; whether the cue came from fish or from other Daphnia; whether the pr esence of fish was sufficient to generate the cue; whether a predator had to be eating and digesting prey; if the type of food was important . 3. Results of the two experiments indicated that : the cue was molec ular. It was only generated by fish digesting live food, unlike bioass ay experiments on Daphnia magna. It did not require that naive Daphnia were pre-conditioned. There was between-clone variation for responses to water conditioned by fish feeding on commercial worms, whereas all the clones tested in these experiments responded strongly to fish fee ding on Daphnia. 4. Between-genotype variation for specificity and sen sitivity to chemical cues suggests the potential for different Daphnia species in different habitats to evolve disparate responses to the sa me kind of predator.