All animals and plants respond to changes in the environment during
their life cycle. This flexibility is known as phenotypic plasticity and
allows organisms to cope with variable environments. A common source of
environmental variation is predation risk, which describes the
likelihood of being attacked and killed by a predator. Some species can
respond to the level of predation risk by producing morphological
defences against predation. A classic example is the production of
pedestals and head spikes in the water flea, Daphnia pulex, which defend
against predation from Chaoborus midge larvae. Previous studies of these
defences have focussed on changes in pedestal size and the number of
spikes along a gradient of predation risk. Although these studies have
provided a model for continuous plasticity, they do not capture the
whole-organism shape response to predation risk. In contrast, studies in
fish and amphibians focus on shape as a complex, multi-faceted trait
made up of different variables. In this study, we analyse how multiple
aspects of shape change in D. pulex along a gradient of predation risk
from C. flavicans. These changes are dominated by the inducible
morphological defence, but there are also changes in the size and shape
of the head and the body. We detected change in specific modules of the
body plan and a level of integration among modules. These results are
indicative of a complex, multi-faceted response to predation and provide
insight into how predation risk drives variation in shape and size at
the level of the whole organism.