Experimental evidence of negative interference in Daphnia magna

Individuals of Daphnia magna Straus living together in groups were found to influence each other in a density-dependent manner. The effect appeared as an inhibition in offspring production and was demonstrated to be induced in part or completely by metabolic products released by Daphnia itself (negative interference). Negative interference was measurable even when there were only two individuals in 50 ml medium (40 animals · 1^-1) and increased up to a density of six animals per 50 ml (120 animals · 1^-1). Also, animals living singly in Daphnia-conditioned water showed a decrease in reproduction. For the measurements a cascade of vessels was developed in which flow-through conditions ensured a constant concentration of algae throughout the system.