Swimming behaviour of Daphnia clones: differentiation through predator infochemicals

Abstract

We studied variation in small-scale swimming behavior (SSB) in four clones of Daphnia galeata (water flea) in response to predator infochemicals. The aim of this study was 3-fold. First, we tested for differences in SSB in Daphnia; second, we examined the potential of differences in SSB to explain survival probability under predation; and third we tested the effect of differences in SSB on survival under predation. Four treatments were applied: one kairomone-free control, one Chaoborus- (phantom midge) and one Perca (perch)-conditioned treatment, and a mixed treatment containing both infochemicals. All of the three tested behavioral parameters (swimming speed, trajectory length and vertical distribution) were affected by the presence of the Chaoborus infochemical, and swimming speed and vertical distribution were also affected by the presence of Perca infochemical. The effect of the treatment was interfered with by a clone effect: genetic differences were pronounced in all traits. These results illustrate that clones can be responsive in only a subset of traits. The general theory that clones are either responsive or non-responsive is not valid for SSB. The outcome of the predation trial confirms that a decrease in activity is a main factor in lowering Daphnia vulnerability to Chaoborus predation.