Morphological and genetic comparisons group 30 species of snapping shrimp (genus Alpheus) into 15 pairs of closely related species. What is the best explanation for the fact that one member of each pair lives on the Atlantic side of the Isthmus of Panama, whereas the other member of each pair lives on the Pacific side?
a. The pairs of species arose by allopatric speciation when the Isthmus of Panama separated their ancestral species.
b. Different predator pressures in the Atlantic and Pacific selected for differences that resulted in the reproductive isolation of these species.
c. These 15 pairs of species illustrate the pattern of punctuated equilibrium in which most speciation events take place in a short period of time.
d. When these pairs meet in a hybrid zone, the reinforcement of reproductive barriers maintains each as a separate species.
e. The 30 species of snapping shrimp evolved by sympatric speciation before the Isthmus of Panama formed
Answer: a. The pairs of species arose by allopatric speciation when the Isthmus of Panama separated their ancestral species.
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