Chapter 21.2: Reproductive Isolation

Reproductive Isolation

The prevention of gene flow between populations that help keep species genetically distinct 

Prezygotic Isolating Factors (Before Fertilization

these mechanisms prevent fertilization from occurring at all among different species → Stops mating or gamete fusion 

• More energy efficient: Does not waste resources on producing inviable embryos 

Types of Prezygotic Isolation

1. Geographic isolation

2. Ecological 

3. Temporal 

4. Behavioral

5. Gametic 

6. Mechanical

Geographic isolation

Populations are separated by physical barriers or distance, so they don’t meet

Ecological Isolation

Species live in the same area but use different habitats or resources and don’t encounter each other

Temporal Isolation

Species reproduce at different times (season, day, or year), preventing mating

Behavioral ISolation

Mating behaviors (courtship rituals, songs, dances) are species-specific, so individuals recognize only their own species

Gametic Isolation

Sperm and eggs are chemically incompatible, preventing fertilization even if they meet

Mechanical Isolation

Physical differences in reproductive organs prevent successful mating

Postzygotic Isolating Factors (After Fertilization):

mechanisms act after the egg is fertilized, preventing the hybrid offspring from becoming fertile, healthy adults

Genetic Incompatibilities

Decreases and become less severe if the species are more closely related

No gene flow

When populations are completely isolated, mutations accumulate independently in each population —> like they aren’t transferred from one population to another due to postzygoting isolating .

Creating genetic incompatibilities

Hybrid Inviability

Postzygotic Isolation

Fertilized egg forms but the embryo fails to develop properly or dies before maturity.

Hybrid Sterility

Postzygotic Isolation

Hybrid offspring survive but are infertile → they can’t reproduce