Question

Identify each scenario as an example of allopatric speciation, sympatric speciation, or neither: Suppose that a mutation evolves in a species of purple-petaled aster that causes individuals with the mutation to have white petals. After the mutation evolves, a chasm forms in the meadow where the asters grow. Pollinators occasionally carry pollen over the chasm, and wind occasionally blows seeds across the chasm, allowing the mutation to spread on both sides of the chasm. One thousand years later, researchers bring purple asters and white asters from both sides of the chasm into the lab. Purple asters from both sides of the chasm successfully interbreed, and white asters from both sides of the chasm successfully interbreed, but no combination of purple asters and white asters interbreed with each other. What kind of speciation occurred in the asters?

1) Allopatric speciation
2) Sympatric speciation
3) Neither

Answer 1

The student's scenario is an example of allopatric speciation due to the geographical separation of aster populations by a chasm that resulted in reproductive isolation and the evolution of two distinct species. The correct option is 1.

Step-by-step explanation:

The scenario you've described is an example of allopatric speciation. In this case, a chasm forms in the meadow, geographically separating the population of asters into two groups. Despite occasional gene flow across the chasm, the two populations, one with purple petals and the other with white petals, ultimately became reproductively isolated from each other. This reproductive isolation, evidenced by the inability of the purple and white asters to interbreed even when brought into contact in the lab, is a hallmark of speciation. Given that the initial separation was due to a geographical barrier (the chasm), which is a key characteristic of allopatric speciation, we can categorize the formation of these new species as such.