Marine biologists are studying stickleback fish populations. There are two distinct variations in the sticklebacks based on phenotypes. They are found with the three spines more commonly in marine ecosystems while they are more commonly found without the three spines in freshwater ecosystems. This has been observed in many marine and freshwater ecosystems across the globe. What explains the variation seen in the image here across different aquatic ecosystems?

Question

Responses
A Differences in genes and expression are seen in the two populations. Selective pressures for the spiny phenotype are more common in marine ecosystems.Differences in genes and expression are seen in the two populations. Selective pressures for the spiny phenotype are more common in marine ecosystems.
B Differences in genes and expression are random across the two populations, causing certain phenotypes to be found in certain ecosystems due to chance.Differences in genes and expression are random across the two populations, causing certain phenotypes to be found in certain ecosystems due to chance.
C Differences in genes and expression are seen in the two populations. Selective pressures for the spiny phenotype are more common in freshwater ecosystems.Differences in genes and expression are seen in the two populations. Selective pressures for the spiny phenotype are more common in freshwater ecosystems.
D Differences in genes and expression are seen in the two populations. Selective pressures against the spiny phenotype are more common in marine ecosystems.

Answer 1

A Differences in genes and expression are seen in the two populations. Selective pressures for the spiny phenotype are more common in marine ecosystems.