Question

List the barriers that prevent interbreeding and give an example of each.

Short answer

Answer: The two main categories of interbreeding barriers are prezygotic and postzygotic barriers. One example of a prezygotic barrier is behavioral isolation, where different bird species have unique mating songs or dances that discourage mating between species. An example of a postzygotic barrier is reduced hybrid fertility, where hybrid offspring are sterile and cannot reproduce, such as the mule, which is a hybrid of a horse and a donkey and is sterile.

Step-by-step solution

Define interbreeding barriers

Interbreeding barriers are factors that prevent individuals of different species from reproducing and producing viable, fertile offspring. These barriers are essential for maintaining the genetic integrity of each species. There are two main categories of interbreeding barriers: prezygotic and postzygotic barriers. Prezygotic barriers prevent the formation of zygotes (fertilized eggs), while postzygotic barriers prevent the development of viable, fertile offspring after zygote formation.

List Prezygotic Barriers

Prezygotic barriers prevent the formation of a zygote. They include: 1. Habitat isolation: Species live in different habitats and rarely meet. Example: One plant species living in a wetland, while another lives in a nearby forest. 2. Temporal isolation: Species breed at different times of the day, season, or year. Example: One species of frog mates in spring, while another mates in autumn. 3. Behavioral isolation: Species have distinct courtship rituals or other behaviors that discourage mating between different species. Example: Different bird species having unique mating songs or dances. 4. Mechanical isolation: Structural differences in reproductive organs make mating impossible. Example: The flowers of one plant species may only be pollinated by specific pollinators that cannot pollinate flowers of a different species. 5. Gametic isolation: Sperm and egg are incompatible due to molecular or biochemical differences, preventing fertilization. Example: The sperm of one species of sea urchin cannot penetrate the eggs of another species because of binding proteins on the egg's surface.

List Postzygotic Barriers

Postzygotic barriers come into play after fertilization and prevent the development of viable, fertile offspring. They include: 1. Reduced hybrid viability: Hybrid offspring have reduced survival rates due to genetic incompatibility. Example: The hybrid offspring of two species of salamanders have a high mortality rate as embryos. 2. Reduced hybrid fertility: Hybrid offspring are sterile and cannot reproduce. Example: The mule, a hybrid of a horse and a donkey, is sterile and cannot breed. 3. Hybrid breakdown: Offspring of hybrids have reduced viability or fertility. Example: Some strains of cultivated rice produce F1 hybrids that are fertile, but the F2 generation has reduced fertility and survival rates. By understanding these various interbreeding barriers and their examples, we can see how species maintain their genetic integrity and how barriers can lead to speciation, which is the process of one species splitting into two or more distinct species.