In the Oceans on Either Side of the Isthmus of Panama

Multiple Choice

In the oceans on either side of the Isthmus of Panama are 30 species of snapping shrimp, 15 species on the Pacific side and 15 different species on the Atlantic side. Species live at different water depths. Morphological and genetic data show that Atlantic and Pacific species that live at similar depths are sister species. The sister species on each side of the isthmus cannot interbreed because the water in the canal is fresh water, not salt water, and provides a barrier to reproduction. A sea-level, salt-water canal between the two oceans has been proposed to make transport across the isthmus easier. Which of the following outcomes is the most likely result if such a canal were built?

A) The sister species will continue to diverge from each other.
B) None of the sister species will interbreed with each other.
C) The Atlantic and Pacific shrimp will continue to live in their respective oceans and not enter the new canal.
D) Shallow-water species from the two oceans that are sister species would be more likely to interbreed with each other than would be deep-water species.