PHENOTYPIC PLASTICITY OF DAPHNIA LIFE-HISTORY TRAITS - THE ROLES OF PREDATION, FOOD LEVEL AND TOXIC CYANOBACTERIA

1. We studied the life history responses of Daphnia pulex under differ ent biotic conditions. In a factorially designed experiment, we tested the impacts of water conditioned by the invertebrate predator Chaobor us, low and high food level (10000 and 100000 Scenedesmus cells ml(-1) ), and exposure to toxic Microcystis (5000 cells ml(-1)) on twelve D. pulex clones originating from different habitats. Our aim was to compa re the phenotypic plasticity of different clones, and to study the int eractions among biotic factors. 2. Individuals cultured in Chaoborus-c onditioned water started to reproduce at a larger size than individual s cultured in water not conditioned by the predators. We found interac tions between food level and Chaoborus-conditioned water on age at fir st reproduction and total offspring number. In addition, the impact of the Chaoborus treatment on the size at first reproduction was reduced by Microcystis exposure. 3. Clonal differences were found in the degr ee of phenotypic plasticity of different life history traits. However, there was no obvious connection between the original habitat of the c lone and the degree of plasticity.