Studies of Snapping Shrimp on Either Side of the Isthmus

Studies of snapping shrimp on either side of the Isthmus of Panama have shown that each Caribbean shrimp species is more closely related to a Pacific shrimp species than it is to any other Caribbean shrimp species. The most likely explanation for this result is

A) snapping shrimp in the Caribbean and the Pacific were never part of the same population.
B) snapping shrimp species were completely diverged prior to the formation of the Isthmus of Panama.
C) the formation of the Isthmus of Panama had no effect on speciation in snapping shrimp.
D) snapping shrimp species diverged after the formation of the Isthmus of Panama.