Swimming behaviour of Daphnia clones: differentiation through predator infochemicals

We studied variation in small-scale swimming behavior (SSB)in four clones of Daphnia galeata (water flea) in response topredator infochemicals. The aim of this study was 3-fold. First,we tested for differences in SSB in Daphnia; second, we examinedthe potential of differences in SSB to explain survival probabilityunder predation; and third we tested the effect of differencesin SSB on survival under predation. Four treatments were applied:one kairomone-free control, one Chaoborus- (phantom midge) andone Perca (perch)-conditioned treatment, and a mixed treatmentcontaining both infochemicals. All of the three tested behavioralparameters (swimming speed, trajectory length and vertical distribution)were affected by the presence of the Chaoborus infochemical,and swimming speed and vertical distribution were also affectedby the presence of Perca infochemical. The effect of the treatmentwas interfered with by a clone effect: genetic differences werepronounced in all traits. These results illustrate that clonescan be responsive in only a subset of traits. The general theorythat clones are either responsive or non-responsive is not validfor SSB. The outcome of the predation trial confirms that adecrease in activity is a main factor in lowering Daphnia vulnerabilityto Chaoborus predation.