Which of the following are examples of a prezygotic barrier to reproduction?
Choose one or more:
A. One oak tree pollinates another oak tree of a different species, resulting in acorns that do not germinate.
B. One fish species’ sperm cannot fertilize the eggs of another fish species.
C. Two birds of different species produce eggs together that hatch, but the offspring die within 24 hours of hatching.
D. One tree species flowers in April-May while another species flowers in August.
The correct answer and explanation is:
The correct answers are:
A. One oak tree pollinates another oak tree of a different species, resulting in acorns that do not germinate.
B. One fish species’ sperm cannot fertilize the eggs of another fish species.
D. One tree species flowers in April-May while another species flowers in August.
These examples illustrate different types of prezygotic barriers to reproduction, which are mechanisms that prevent fertilization from occurring between individuals of different species.
- Prezygotic barriers operate before fertilization, preventing mating or fertilization from taking place. These barriers can be physical, temporal, or behavioral. Example A, the inability of acorns from different oak species to germinate, indicates that fertilization may have occurred, but post-fertilization barriers prevented the offspring from being viable, which is more of a postzygotic barrier. However, the focus here is on prezygotic barriers, which can include mechanisms like temporal isolation (Answer D) or gametic incompatibility (Answer B).
- Answer A illustrates a form of gametic isolation, where even if pollination occurs, the resulting gametes (in this case, the acorns) are incompatible and cannot produce viable offspring. This is a classic example of a prezygotic barrier since fertilization between the different species’ gametes fails to lead to a viable embryo.
- Answer B describes gametic isolation, a prezygotic mechanism where the sperm from one species cannot fertilize the eggs of another species. This is a barrier because it directly prevents successful fertilization from occurring.
- Answer D represents temporal isolation, a prezygotic mechanism where two species reproduce at different times (in this case, flowering at different times of the year). This timing difference prevents them from mating with each other and results in reproductive isolation.
On the other hand, Answer C is not an example of a prezygotic barrier. It describes a situation where offspring can be produced, but they die shortly after hatching. This scenario points to a postzygotic barrier, where the offspring are not viable after fertilization has occurred.