Predator-specific responses of Moina macrocopa to kaironmones from different fishes

Cladoceran species are important model organisms for studying aquatic ecology and evolution and are textbook examples of inducible defense against predators. To test the defense traits of Moina macrocopa in response to different fish species that co-occur or do not co-occur with the prey species in their native habitat, we conducted experiments with the three fish species Rhodeus ocellatus (wild species), golden fish Carassius auratus (artificial breeding species), and Danio rerio (model organism used in laboratories). We measured the size at maturity, time to reproduction, size of brood, and the moving rate of M. macrocopa. This crustacean species exhibited earlier reproduction time and increase in offspring number when exposed to R. ocellatus kairomone. Such changes in the life history of M. macrocopa in response to R. ocellatus were more sensitive than those to artificially raised fish (C. auratus and D. rerio). In addition, the moving rate of Moina exposed to R. ocellatus kairomone was significantly lower than to other tested fish species after the third instar stage. We found a coupling of life history and behavior-related responses evoked by R. ocellatus kairomone. These results provide evidence supporting energy re-allocation between life history and behavior in inducible defenses of M. macrocopa.