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The blue mussel, Mytilus edulis, lives along the northeastern coastline of the USA - VCE - SSCE Biology - Question 4 - 2010 - Paper 1
Question 4
The blue mussel, Mytilus edulis, lives along the northeastern coastline of the USA. A species of Asian shore crab, Hemigrapsus sanguineus, was accidentally introduce... show full transcript
Worked Solution & Example Answer:The blue mussel, Mytilus edulis, lives along the northeastern coastline of the USA - VCE - SSCE Biology - Question 4 - 2010 - Paper 1
Step 1
a. Explain the process of natural selection that has occurred in the population of southern blue mussels over the last 15 years that has resulted in thicker shells.
Answer
Natural selection occurs when there is variation in a population and certain traits provide a survival advantage. In the case of southern blue mussels, there has been an observed variation in shell thickness, with thicker shells providing better protection against predation by the Asian shore crab.
Crabs are selective predators and preferentially feed on mussels with thinner shells, leading to a higher mortality rate among those individuals. Over time, mussels with thicker shells are more likely to survive, reproduce, and pass on this advantageous trait to their offspring. This creates a shift in the population towards thicker shells as a result of the increased survival and reproductive success of the thicker-shelled mussels in the environment dominated by the Asian shore crab.
Step 2
b. What would you expect to happen to the shell thickness of the northern blue mussels over time? Explain your reasoning.
Answer
If the Asian shore crab is unable to migrate into the northern blue mussel area, the selective pressure exerted by the crabs will be absent. As a result, the shell thickness of the northern blue mussels is expected to remain stable or even decrease over time. Without the threat of predation favoring thicker shells, there would be no significant advantage to maintaining this trait. Thus, genetic variation related to shell thickness may result in a population where thinner shells become more common, as these individuals might allocate energy towards other growth or reproductive strategies.