Question

An new interstate highway separates brown and white populations of a species of desert lizard. Eventually, the two morphs can no longer mate. This is an example of prior selection followed by biological speciation. A. directional; allopatric B. directional; sympatric C. disruptive; allopatric D. disruptive; sympatric E. stabilizing; lack of

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Answer 1

This is an example of prior disruptive selection followed by allopatric biological speciation.

The three types of natural selection are stabilizing, directional and disruptive. For example, let us consider that the lizard has two extremes of color viz. brown and white. In stabilizing selection, the population moves towards an average phenotype. If the natural population was more of intermediates of brown-and-white, this would be termed stabilizing selection. In directional selection, one of the two extremes are selected, i.e. if the majority of lizards in the population were only either brown or white, it would be a case of directional selection. However, the lizards naturally occurred in two populations of brown and white. This is an example of disruptive selection, where two (or more) extreme phenotypes occur naturally in high frequencies.

After having been separated by the highway for some time, the two populations cannot interbreed. This is a typical example of allopatric speciation, also known as geographic speciation. This type of speciation results from two populations being isolated by geographical structures (such as splitting of continents or formation of new mountains, and in this case, just a highway) for a period of time that the two populations cannot interbreed. The reason for not being able to interbreed is that the two isolated populations undergo different types of mutations, selections and genetic drifts that make them two different species.