Question

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 closely related species, with one species of each pair in the Pacific and the other in the Caribbean. The different species pairs live at different depths in the ocean. Using mitochondrial DNA sequences, the researchers estimated phylogenies and found that each of these species pairs (sister species), 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.

1. These species are distinctive species under all three species concepts.

a. Likely

b. Not Likely

2. Sympatric speciation caused the difference between the seven species on the Pacific side.

a. Likely

b. Not Likely

3. Sympatric speciation caused the differences between the sets of sister species on either side of the Isthmus.

a. Likely

b. Not likely

4. If sea levels rises enough to cover the isthmus, the sister species on either side of the isthmus will likely undergo fusion.

a. Likely

b. Not likely

5. Habitat isolation is the only reproductive isolating barrier preventing the formation of hybrid from the different sister species.

a. Likely

b. Not likely

6. If sea levels rise enough to cover the isthmus, the frequency of hybrid offspring would decrease.

a. Likely

b. Not likely

7. What other type of reproductive isolating barrier is creating the reinforcement of differences between the sister (closely related) shrimp species pairs?

a. Behavioral isolation

b. Gametic isolation

c. Temporal isolation

d. Reduced hybrid fertility

e. Both A and D

Answer 1

1. (a) Likely

The species on either side are distinctive species in accordance with all three species concept - morphological, biological and phylogenetic species concept.

2. (a) Likely

The species present on the same side, i.e, Pacific side shares the same geographical area thereby giving rise to sympatric speciation.

3. (b) Not likely

The sister species are geographically isolated. So they couldn't have arised due to sympatric speciation.

4. (b) Not likely

When the sister species meet again, they can fuse only if they produce viable, fertile offsprings. But lab study shows that they produce mostly infertile offsprings.

5. (b) Not likely

Apart from habitat isolation, there is behavioral isolation as well. Moreover, they don't produce fertile offsprings.

6. (b) Not likely

The sister species can interbreed and produce inferior offsprings (mostly infertile hybrids)

7. (e) Both A and D

In the lab, the sister shrimp species pair were not very interested in mating (behavioral isolation) and they did not produce fertile offsprings (reduced hybrid fertility)

(Please rate the answer if found helpful)