Reproductive Isolation Flashcards
What is reproductive isolation (RI), and how does it reduce gene flow between populations?
Reproductive isolation is the reduction of gene exchange between populations due to biological differences (reproductive isolating barriers) between them. It limits interbreeding and facilitates speciation.
Can gene flow ever be completely reduced between populations? Why or why not?
No, gene flow is never completely reduced. Reproductive isolation occurs on a continuum and may not be absolute.
How does reproductive isolation accumulate during speciation?
Reproductive isolation accumulates as species diverge, with barriers to interbreeding strengthening over time. Some isolation may collapse, leading to a single population again.
Give an example of species previously treated as the same but now recognized as distinct due to reproductive isolation.
European Red Deer (Cervus elaphus) and North American Elk (Cervus canadensis) were once treated as one species. Despite producing fertile offspring in captivity, they differ in gestation, size, and mating calls.
What are the three main roles of reproductive isolation in speciation?
Limits gene flow, facilitating adaptation and divergence.
Prevents merging of distinct species, maintaining separation.
Defines reproductive communities, ensuring species cohesion.
How can initial barriers to interbreeding be augmented over time?
New barriers may arise after the initial separation, reinforcing the reproductive isolation between populations.
What is the difference between reproductive isolation and isolating barriers?
Reproductive isolation is the reduction in gene exchange, while isolating barriers are specific mechanisms (e.g., geographic separation, mating behaviors) that act to prevent or reduce interbreeding.
How are isolating barriers classified based on timing?
Pre-mating barriers: Prevent gamete exchange.
Post-mating, prezygotic barriers: Prevent zygote formation.
Postzygotic barriers: Reduce hybrid viability or fertility.
Why does the order of action of isolating barriers matter?
The order affects the overall contribution to reproductive isolation and the resources wasted in unsuccessful interspecific interactions.
What is geographic isolation, and how does it act as a pre-mating barrier?
Geographic isolation is the physical separation of populations, preventing interbreeding. For effectiveness, the separation must be permanent or long-lasting.
Provide examples of behavioral and mechanical isolation as pre-mating barriers.
Behavioral isolation: Meadowlarks with overlapping ranges do not recognize each other’s songs.
Mechanical isolation: Incompatible genital structures prevent mating.
What happens in post-mating, prezygotic isolation?
Fertilization fails even after mating. For example, sea urchins with differing sperm-egg recognition proteins cannot interbreed.
What are postzygotic barriers, and how are they measured?
Postzygotic barriers reduce hybrid fitness, viability, or fertility. They are measured by comparing hybrid survival and reproductive success to non-hybrids.
Differentiate between intrinsic and extrinsic postzygotic barriers.
Intrinsic barriers: Independent of the environment (e.g., mules’ sterility).
Extrinsic barriers: Dependent on environmental factors (e.g., hybrid pollinator preference).
Provide an example of intrinsic hybrid sterility.
Mules, the sterile offspring of a horse and donkey, result from chromosomal differences between the parents.
