Question

In a species of snail, dark-shelled individuals are better hidden from bird predators in the shady forest, while light-shelled individuals are better hidden in well-lit brushy edge areas. If there were no areas of intermediate brightness in this habitat,which type of selection would act on shell color in these snails?

Stabilizing selection
Disruptive selection
Directional selection

Answer 1

The correct answer is: Disruptive selection

Disruptive selection is a type of natural selection that favors both extreme traits in a population (it is bimodal) over intermediate traits. In the example above, it favors dark and light-snails (both are extreme traits). As a consequence, the population of snails is divided into two distinct groups. This happens because snails with intermediate brightness wouldn’t have suitable environment for them, wouldn’t be adopted to either shady forest or brushy edge areas.