Final answer:
It is true that water fleas (Daphnia pulex) exhibit polyphenism by producing different tail lengths depending on predator presence, exemplifying adaptation and phenotypic plasticity.
Step-by-step explanation:
The statement that water fleas (Daphnia pulex) produce either long or short spiky tails depending on the presence of predators in their environment is an example of polyphenism is True.
Polyphenism refers to a single genotype producing multiple phenotypes depending on environmental conditions. In the case of Daphnia pulex, when predators are present, they tend to develop longer spiky tails, which may provide a defensive benefit against predation.
This remarkable biological process shows how organisms can adapt their physical traits in response to ecological pressures, reinforcing the concepts of adaptation and phenotypic plasticity.