Optimising survival under predation: chemical cues modify curvature in Daphnia galeata

Morphological responses to the presence of predator info-chemicals havebeen described for many Daphnia (Cladocera) species, butD. galeata is generally considered to exhibit almost nomorphological changes that could increase its fitness under predation.Therefore, the aim of our study was to examine the nature and magnitude ofmorphological responses of D. galeata to their predatorsindetail and assess their potential role in decreasing the predation threat. Twoclones of Daphnia were exposed to predator info-chemicals(kairomones) from perch, a fish (Perca), and a phantommidge larvae (Chaoborus) an invertebrate, and a kairomone mixture fromboththese organisms. Laboratory life-table experiments were carried out and fiveparameters characterising the body shape of the daphnids were measured: helmetlength, head- and carapace width, eye diameter and body size. The last-namedthree parameters did not differ significantly between the clones or thetreatments. The differences found between the clones were significant for headwidth and helmet length, but only in combination with the treatment effects.Ourresults on genotype-dependent phenotypic plasticity indicated that, althoughphenotypic plasticity is present, the clonal composition of aDaphnia population can be altered by selection on themorphotype. This potential for a change in clonal frequencies is given by thedifferences measured between the two clones in head width and helmet length,altering the curvature of the Daphina body in response tokairomone presence.