RELATIONSHIPS BETWEEN MIXIS IN BRACHIONUS-PLICATILIS AND PRECONDITIONING OF CULTURE-MEDIUM BY CROWDING

Several experiments with Brachionus plicatilis have been conducted to test the existence of chemical-mediated induction of mixis. In a first experimental set, bioassays were used to test relationships between preconditioning of culture medium to high population density and the occurrence of mixis in mass cultures with these media. The results show that a preconditioned medium has inducing properties that are comparable to the crowding effect. In order to isolate the effect on mixis of the preconditioning, we also carried out an experiment involving individual cultures. Isolated individuals of B. plicatilis, CU strain, placed in 1 ml of medium renewed daily showed no mixis, but mixis was induced when medium preconditioned to high density was used following the same experimental procedure.