The desert population of spiny cacti are under attack. Peccaries are eating those plants with low-spine-number causing their alleles to vanish from the gene pool and enriching the remaining gene pool in those alleles that create cacti with high-spine-numbers. At the same time, a parasitic insect eats the cacti with a high spine number. The two extremes in spine number in the population are vanishing. Which kind of selection do we observe?

A. Directional selection.

B. Stabilizing selection.

C. Disruptive selection.

B. Stabilizing selection.

Explanation:

In a population, natural selection can favor one of the many phenotypes present. Directional selection is the phenomena where one of the extreme phenotypes is favored. Disruptive selection is the phenomena where both the extreme phenotypes are favored over the average phenotype. In stabilizing selection, the extreme phenotypes are not preferred so that maximum organisms fall under the average category.

Here, low spine number cacti are being eaten by peccaries and high spine number cacti are being eaten by a parasite. Both of these extreme phenotypes are under attack which will favor the cacti with average number of spines to survive. Hence, this is an example of stabilizing selection.