Prezygotic barriers prevent the formation of a zygote, the first cell of a new organism, by disrupting mating or fertilization. One example of a prezygotic barrier is the difference in mating behavior between two closely related species.
Behavioral Isolation
Behavioral isolation occurs when two species do not mate because they have different courtship rituals or mating seasons. For example, in the damselfly genus Calopteryx, two species, C. splendens and C. virgo, have different courtship displays. C. splendens males perform a “vibration dance” in the air, while C. virgo males perform a “side-to-side” dance on the ground. These different displays prevent the two species from mating.
Another example of behavioral isolation is the difference in mating seasons between two species of fireflies. In the genus Photuris, some species mate in the spring, while others mate in the fall. This difference in mating seasons prevents the two species from mating.
Other Types of Prezygotic Barriers
In addition to behavioral isolation, there are other types of prezygotic barriers, including:
- Mechanical isolation: This occurs when the reproductive structures of two species are not compatible. For example, in the fig genus Ficus, the size of the fig may prevent different species of fig wasps from entering the fig and pollinating the flowers.
- Gametic isolation: This occurs when the gametes (eggs and sperm) of two species are not compatible. For example, in the sea urchin genus Strongylocentrotus, the sperm of one species may not be able to penetrate the eggs of another species.
- Ecological isolation: This occurs when two species live in different habitats and do not come into contact with each other. For example, in the salamander genus Plethodon, some species live in forests, while others live in caves. This difference in habitat prevents the two species from mating.
Importance of Prezygotic Barriers
Prezygotic barriers are important because they prevent the formation of hybrids, which are often inviable or less fit than their parents. Hybrids may have difficulty surviving in the wild because they have traits that are not suited to either of their parent species. For example, in the case of the fireflies mentioned above, hybrids between a spring-mating species and a fall-mating species may have difficulty surviving because they are not adapted to either mating season.
Prezygotic barriers also help to maintain the genetic integrity of species. By preventing interbreeding between different species, prezygotic barriers help to prevent the loss of unique genetic traits.
Conclusion
Prezygotic barriers are an important part of the reproductive process. They help to prevent the formation of inviable or less fit hybrids and maintain the genetic integrity of species.