Daphnia longicephala is a freshwater crustacean that can detect chemical cues produced by the predator Notonecta glauca. Researchers raised Daphnia clones and observed that those exposed to Notonecta chemical cues during their development produced larger protective crests. Crest height and width are measured as ratios to body length. The increase in the size of the crest width and height is not associated with a corresponding change to the Daphnia’s genome. Researchers hypothesize that growing a crest is energetically costly, so Daphnia does not develop the large crests in the absence of Notonecta.

b. Explain how the presence of Notonecta chemical cues affects gene expression in the Daphnia.