mussel defenses induced by the presence ofcrabs?Hypothesis: Mussels increase investment in defense in the presence ofcrabsNull hypothesis: Mussels do not increase investment in defense inthe presence of crabsExperimental setup:SeawaterNo crabCrab(fed fish, not mussels)MusselsMusselsPrediction: Mussels downstream of the crab tank will have thickershells than mussels downstream of the empty tank.Prediction of null hypothesis: Mussels in the two tankswill have shells of equal thicknessResults:0.6-0.4-0.200No crabCrabWhat conclusion can you draw from the figure above?Without direct contact, mussels can sense the presence of crabs.O Mussels can sense the presence of crabs only visually.O Mussels are increasing their shell thickness in response to water current.Shell thickness is a non-inducible defense.O Crabs hunt for mussels by focusing on the chemicals they emit into the water.Shell thickness lmm)

Mussels belong to the phylum mollusks and inhabit both fresh and marine intertidal water bodies. Their external shell is composed of two halves joined by a ligament. In the juvenile stage, the small size and loose attachment of mussels made them vulnerable to predation.The inducible defense is one of the common defense strategies found in both aquatic and terrestrial organisms. The marine mussels present in the shorelines with low water flow experience high crab predation. The mussels in such areas which high crab predation have comparatively thicker shells and are attached to the substratum more tightly. The thicker shells are formed in response to the chemical cues from crabs. Without direct contact, mussels can sense the presence of crabs as the chemical cues from crabs can reach mussels present downstream of the crab tank along with the water current. Thus, this option is best suited to draw the conclusion for increased mussel shell thickness. Mussels can sense the presence of crabs only visually. It is a wrong conclusive statement as mussels are present downstream and can not see crabs. However, the shell thickness of mussels in both tanks is different. Mussels do not increase their shell thickness in response to the water current. If that was the case, then there must be no difference in the shell thickness as the water is current is the same in both the tanks. Shell-thickness is an inducible defense strategy. Mussels increase their shell thickness to decrease the predation rate. Thick shells increase the handling time for foraging crabs. Crabs hunt for mussels by focusing on the chemicals they emit into the water is not the case here. The chemical cues are emitted by the crabs in response to which the mussels increase their shell size. Secondly, the direction of water current is from carbs to mussels and not from mussels to crabs.Answer: without direct contact, mussels can sense the presence of crabs.