Question

in 1964, the south coast of alaska experienced the largest earthquake ever recorded in north america. over a period of a few minutes, the earthquake uplifted new islands out of the gulf of alaska. water trapped in depressions as the islands uplifted formed isolated saltwater ponds on the surfaces of the islands. the ponds on three of these newly-formed islands contained members of the same population of threespine stickleback (gasterosteus aculeatus), a type of fish.
scientists have monitored the stickleback populations in these ponds since the 1964 earthquake. which of the following are these scientists most likely to observe over time?

a. the sticklebacks remain a single species because the ponds have similar environmental conditions.

b. the sticklebacks remain a single species because of their shared genetic history.

c. the sticklebacks diverge into separate species as a result of different selection pressures in each pond.

d. the sticklebacks rapidly go extinct because they cannot adapt to the new conditions.

Explanation:

This problem is about evolutionary biology, specifically allopatric speciation. The sticklebacks are in isolated ponds (geographic isolation). Different ponds will have different selection pressures (e.g., food availability, predators, water chemistry), leading to different adaptations. Over time, these differences can accumulate, causing the populations to diverge into separate species. Option A is wrong because even similar environments can have subtle differences, and isolation allows divergence. Option B is wrong because shared genetic history alone doesn't prevent speciation—genetic changes can occur in isolation. Option D is wrong as sticklebacks are adaptable to new environments, so rapid extinction is unlikely.

Answer:

C. The sticklebacks diverge into separate species as a result of different selection pressures in each pond.