Reproductive Isolating Mechanisms

Reproductive Isolating Mechanisms

Any heritable feature of body form, function, or behavior that prevents interbreeding between one or more genetically divergent populations Results as a by-product of genetic divergence Maintains positive adaptations for specific environments 1. Prezygotic Isolating Mechanisms 2. Postzygotic Isolating Mechanisms

Hybrid Inviability

Egg of one species is fertilized by sperm from another species, but fertilized egg cannot develop past early embryonic stages

Gametic Isolation

Incompatibility gametes of different species are incompatible at the molecular level resulting in mortality

Ethological Isolation

Isolated by behaviors Copulation proceeded by courtship displays Reciprocity produces sexual stimulation Ex: Birds, some can not recognize the mating signals of other birds

Geographic Isolation

Isolated by distance or geographic barriers (Do not come in contact) Distance or barrier relative to the size of the organisms Ex: Head lice and body lice Geographic isolation is the hairless region of the neck

Mechanical Isolation

Isolated by incompatible reproductive part size or shape Mechanical isolation is often severe, wrong mating types can result in mortality to both males and females "Key doesn't fit the whole"

Temporal Isolation

Isolated by reproductive events that occur at different times (mating, flowering days or seasons do not overlap) Ex: Cicadas

Ecological Isolation

Isolation due to adaptation to different microclimates in the same habitat Ex: California Oaks - 3 species Separation is based on physiological mechanisms to promote conservation of water

Postzygotic Isolating mechanisms

Mechanisms of isolation after fertilization 1.Zygotic Wastage 2. Hybrid Sterility 3. Hybrid Inviability 4. Hybrid Breakdown

Prezygotic Isolating Mechanisms

Mechanisms of isolation before or during fertilization 1.Ecological Isolation 2. Geographic Isolation 3. Temporal Isolation 4. Ethological Isolation 5. Mechanical Isolation 6. Gamete Isolation

Zygotic Wastage

Minimum # of zygotes required per species to achieve a viable adult

Hybrid Sterility

No viable sperm or egg

Hybrid Breakdown

Offspring fertile but their offspring are sterile or have genetic abnormalities (hybrids have low fitness)

Gametic Wastage

minimum # of sperm required per species to achieve fertilization