About 3 million years ago, the isthmus of panama (a narrow strip of land connecting north and south america) formed, dividing marine organisms into pacific and caribbean populations. researchers have examined species of snapping shrimp on both sides of the isthmus. based on the morphological species concept, there appeared to be seven pairs of species, with one species of each pair in the pacific and the other in the caribbean. the different species pairs live at somewhat different depths in the ocean. using mitochondrial dna sequences, the researchers estimated phylogenies and found that each of these species pairs, separated by the isthmus, were indeed each other's closest relatives. the researchers investigated mating in the lab and found that many species pairs were not very interested in courting with each other, and any that did mate almost never produced fertile offspring.

refer to the paragraph about the formation of the isthmus of panama. the sister populations on opposite sides of the isthmus are true species under which species concept?

a) the biological species concept
b) the phylogenetic species concept
c) the morphological species concept
d) the morphological species, biological species, and phylogenetic species concepts