In the oceans on either side of the Isthmus of Panama are 30 species of snapping shrimp; some are shallow-water species, others are adapted to deep water. There are 15 species on the Pacific side and 15 different species on the Atlantic side. The Isthmus of Panama started rising about 10 million years ago. The oceans were completely separated by the isthmus about 3 million years ago.
In the figure, the isthmus separates the Pacific Ocean on the left (side A) from the Atlantic Ocean on the right (side B). The seawater on either side of the isthmus is separated into five depth habitats (1-5), with 1 being the shallowest.

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In which habitat should one find snapping shrimp most closely related to shrimp that live in habitat A4?
In which habitat should one find snapping shrimp most closely related to shrimp that live in habitat A4?
A) A3
B) A5
C) B4
D) either A3 or A5

Question

In the oceans on either side of the Isthmus of Panama are 30 species of snapping shrimp; some are shallow-water species, others are adapted to deep water. There are 15 species on the Pacific side and 15 different species on the Atlantic side. The Isthmus of Panama started rising about 10 million years ago. The oceans were completely separated by the isthmus about 3 million years ago.
In the figure, the isthmus separates the Pacific Ocean on the left (side A) from the Atlantic Ocean on the right (side B). The seawater on either side of the isthmus is separated into five depth habitats (1-5), with 1 being the shallowest.

-
In which habitat should one find snapping shrimp most closely related to shrimp that live in habitat A4?
In which habitat should one find snapping shrimp most closely related to shrimp that live in habitat A4?
A) A3 
B) A5 
C) B4 
D) either A3 or A5

Quizplus · Accepted Answer

Snapping shrimp on Side A are separated from those on Side B by the Isthmus of Panama. The isthmus has risen slowly over the last 10 million years, and the oceans were completely separated from each other about 3 million years ago. Therefore, snapping shrimp on Side A and Side B are likely to have evolved separately for about 3 million years. Snapping shrimp in the same habitat on opposite sides of the isthmus should be more closely related to each other than to shrimp in different habitats on their own side. The snapping shrimp most closely related to habitat A4 should be in a different habitat on Side B, which is habitat B4. Therefore, the answer is C.

In the Oceans on Either Side of the Isthmus of Panama