[Campbell Biology P.749] Considering the previous research, the experimental results, and th... | Practice Question

Considering the previous research, the experimental results, and the concept of natural selection, which conclusion is best supported regarding the flat periwinkle populations in the Gulf of Maine?

  • A: Southern periwinkles have evolved thicker shells due to stronger selective pressure from European green crabs, making them more resistant to predation than northern periwinkles.
  • B: Northern periwinkles are inherently more susceptible to predation, regardless of crab origin, indicating a lack of adaptive evolution.
  • C: The observed differences in predation rates are solely due to differences in crab foraging tactics between northern and southern populations.
  • D: The thicker shells observed in southern periwinkles are a direct phenotypic response to the presence of crabs, rather than a genetic adaptation.

Explanation

The previous research indicates that southern periwinkles, exposed to green crab predation for over 100 generations, have developed thicker shells than both historical populations and contemporary northern populations. The experimental results show that southern periwinkles are indeed more resistant to predation by both northern and southern crabs. This pattern is consistent with natural selection favoring individuals with stronger defenses thicker shells in areas with long-term, intense predation pressure.