Stickleback fish exhibit variation in a morphological trait known as gill rakers. Fish with long gill rakers are very good at eating plankton, and fish with short gill rakers are good at eating deep-water invertebrates. However, fish with intermediate-length gill rakers are poor at eating either type of food. Fish that are better at consuming food have higher survival and reproduction rates than poorer consumers. Based on this information, what type of selection is likely acting on stickleback gill raker length?

a, no natural selection
b, stabilizing selection
c, disruptive selection
d, directional selection

Disruptive selection is a term used to describe population genetic changes that simultaneously favor individuals at both ends of the distribution. When disruptive selection operates, individuals at the extremes contribute more offspring than those with intermediate characteristics, producing two peaks in the distribution on a graph.

In the excerpt shown in the question, long-gill-striped and gill-striped fish were favored by the selection process than intermediate-length striped fish. For this reason we can conclude that a disruptive selection was taking place.