Clonal variation in depth distribution of Daphnia pulex in response to predator kairomones

In this laboratory study, we explored the variability of 47 Daphnia pulex clones in migration behavior to predator (Chaoborus and fish) kairomones in 1.6 m long tubes. The preferred mean vertical distribution in control water (no predator kairomone) is diverse among clones and responses to predator kairomone are highly variable. Some migration patterns were opposite to our expectations in clones exhibiting an upward migration in response to fish kairomone. A literature comparison indicated that this is not an unusual finding. In general, more clones responded to Chaoborus than to fish kairomone, stressing the importance of Chaoborus as a predator for Daphnia in nature. Dilution of Chaoborus kairomone led to a reduced upward migration by most Daphnia pulex clones tested and adult Daphnia exhibited a strongly reduced response to Chaoborus in comparison to juvenile Daphnia. This indicates that Daphnia may be able to respond to the actual predation threat.