Question

5) Many songbirds breed in North America in the spring and summer, and then migrate to Central and South America in the fall. They spend the winter in these warmer areas where they feed and prepare for the spring migration north and another breeding season. Two hypothetical species of sparrow, A and B, overwinter together in mixed flocks in Costa Rica. In spring, species A goes to the east coast of North America, and species B goes to the west coast. What can you say about the isolating mechanisms of these two species? A) They must have strong postzygotic isolating mechanisms to spend winter in such close proximity. B) They must have strong prezygotic isolating mechanisms to spend winter in such close proximity. C) These two species mate in different climates. D) Reinforcement must be occurring when they winter together.

Answer 1

Answer is C.

Explanation:

The two species do not breed in the same area, so they are reproductively isolated by allopatry.

Allopatry means that these two species are geographically separated during the breeding season, so they are reproductively isolated.

Allopatric speciation is a form of speciation (creation of new species) that occurs as a result of geographic isolation. This means that a part of population becomes physically separated from the initial main population. There is no gene flow between these two populations and as a result the two populations reach a high level of genetic divergence. They can no longer interbreed which means they become two different species (speciation). Hence we can eliminate the Options A,B and D.