Disruptive selection is a key component of sympatric speciation because it acts against the homogenizing effect of gene flow between the diverging populations. Imagine a case in which a bird population is undergoing disruptive selection on bill size in response to the availability of seeds to eat. The birds' environment contains two seed types, large and small, and lacks medium-sized seeds. Assume that a bird's ability to eat a seed is a direct function of its bill size (large bills are good for large seeds, and so on). Disruptive selection acts against birds with:
A)large bills.
B)small bills.
C)large bills and birds with small bills.
D)intermediate (medium-sized)bills.
E)medium bills and birds with large bills.

Question

Quizplus · Accepted Answer

Disruptive selection favors extreme phenotypes and acts against intermediate ones. In this case, birds with intermediate (medium-sized) bills will be at a disadvantage as they cannot efficiently eat either large or small seeds. Thus, disruptive selection will act against birds with intermediate bills and promote the emergence of two distinct bill sizes, one suited for large seeds and the other for small seeds.

Disruptive Selection Is a Key Component of Sympatric Speciation Because