Maternal contributions to individual behavior in Daphnia

In a laboratory experiment conducted in thermally stratified glass tubes, so-called "plankton organs", we tested two alternative hypotheses concerning the role of maternal effects on Daphnia vertical migration behavior induced by the presence of a fish predator. The first hypothesis states that maternal experience does not influence the induction of this behavior because it is quickly induced and does not require information about the persistence of the threat. The second hypothesis states that maternal fear increases the intensity of the individual responses of their descendants to the threat. However, both hypotheses turned out to be false. Fear experienced by the mother discourages offspring from incurring the costs of defense. The obtained results allow to hypothesize that the process of optimizing defense mechanisms may integrate decisions across several generations and include compensation for costs of defense in the previous generation. Regardless of the need to further validate this hypothesis, our results demonstrate the complexity of optimizing the induction of defense mechanisms in Daphnia.