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.

Crustacean Daphnia longicephala lives in freshwater that can detect chemical cues produced by the predator Notonecta glauca and in response of these chemicals the Daphnia produces crest for defense purpose.

Explanation:

Notonecta glauca is a predator which feeds on Daphnia longicephala. For protection from predator Daphnia produces crest which is a defense mechanism in the Daphnia against Notonecta. This defense is associated with the chemical produces by Notonecta . So we can say that the chemical is responsible for the formation in crest in Daphnia which does not formed in normal condition.

if you listed your answers right then i believe your answer is b.

ok yes, but what is the question? as soon as you ask the actual question i will answer it. : )