Our example introduces us to H. davidii and H. fortii, which are two closely related species of orchids. So, we're talking about flowers here. For each statement below, if the statement represents a prezygotic barrier, write "pre" on the line. If the statement represents a postzygotic barrier, write "post" on the line.
If the statement does not represent a reproductive barrier, write "none" on the line. Let's remember the distinction between prezygotic and postzygotic barriers:
- Prezygotic barriers occur before fertilization.
- Postzygotic barriers occur after fertilization.
Let's check out our options here:
A) Both flowers are found in the same region.
Well, if they're found in the same region, that does not sound like a barrier to reproduction, so we should write none.
B) When fertilized by pollen of the other species, hybrids fail to produce seeds.
This involves the creation of hybrids, and since it's a problem that occurs after the zygote is formed, it is a postzygotic barrier. The hybrids are sterile, indicating a barrier to successful reproduction.
C) H. davidii and H. fortii are both pollinated by a single pollinator, the hawk moth.
A single pollinator implies potential cross-pollination between the two species, so it is not a barrier. Write none on the line.
D) Both flowers bloom in July.
If they bloomed at different times, that might be a barrier, but since they bloom simultaneously, there's no barrier here. Thus, the answer is none.
E) The species' unique flower structures release pollen on different body parts of the pollinator, so pollen is not transferred between the two species.
Since the pollen isn't transferred, there's no opportunity for fertilization between the two species, indicating a prezygotic barrier.
With that, we conclude our analysis. More practice after this and give it a try.
