Study design
We used data originally collected in Dennis et al. 2011. This
included photographs of second and third instar D. pulex exposed
to six different concentrations of C. flavicans kairomone,
including a control (0, 0.1, 0.25, 0.5, 0.75 and 1µl
ml-1). Animals were photographed at the second and
third instar because this is when the defence is usually expressed the
most . For each treatment, third-generation mothers of at least their
third brood had been exposed to the relevant cue concentration and
offspring of the subsequent brood were transferred to glass jars which
contained 50ml of hard artificial pond water, food (2 x
105 cells ml-1 of algae) and the
appropriate concentration of predator cue. Animals were transferred to a
new jar containing fresh media and cue daily, until they reached
maturity. Photographs of the animals were taken at the second and third
instars.
Three genotypes were analysed for shape plasticity from this dataset.
Two (clones Chardonnay and Cletus) showed a characteristically low level
of induced morphology and one (clone Carlos) a characteristically high
level. Animals from second and third instars were pooled so the data
formed a factorial design of six predation risk levels x three
genotypes. There were 5-10 replicate photos (i.e. replicate individuals)
at each level of predation risk for each clone (totalling 518 photos).