Module #3 | Lecture #6: Reproductive Isolation

Reproductive Isolation Mechanisms

Any heritable feature of body form, function, or behavior that prevents interbreeding between one or more genetically divergent populations

• by-product of genetic divergence

• Maintains positive adaptations for specific environments

Prezygotic isolating mechanisms

Mechanism of isolation before or during fertilization

Postzygotic isolating mechanisms

Mechanisms of isolation after fertilization

Ecological isolation

A type of prezygotic isolation due to adaptation to different microclimates in the same habitat

ex: california oaks have 3 species

• Separation is based on physiological mechanisms to promote conservation of water

Geographical isolation

Prezygotic isolation by distance or geographic barrier

• organisms do not come into contact

• ex: Lice

  • Head lice and body lice are isolated by the hairless region of the neck

Temporal Isolation

Prezygotic isolation by reproductive events that occur at different times

ex: mating and flowering days or seasons do not overlap

Ethological isolation

Prezygotic isolation by behaviors

• copulation proceeded by courtship displays

Mechanical isolation

Prezygotic isolation by incomparable reproduction part size or shape

• often severe isolation and can result in mortality to both males and females

Gametic isolation

Prezygotic isolation as gametes of different species are incompatible at the molecular level resulting in mortality

Gametic Wastage

Minimum # of sperm required per species to achieve fertilization

Zygotic wastage

Postzygotic isolation where a minimum # of zygotes are required per species to achieve a viable adult

ex: Fish, nemo (all those eggs and just one Nemo)

Hybrid sterility

Postzygotic isolation where there is no viable sperm of egg

Hybrid Inviability

Postzygotic isolation where an egg of one species is fertilized by sperm from other species, but fertilized egg cannot develop past embryonic stages

Hybrid breakdown

Postzygotic isolation where offspring are fertile but their offspring are sterile or have genetic abnormalities (hybrid have low fitness)

Postzygotic isolation

Isolation that takes effect after fertilization

• Unsuitable interactions among individuals, gene or gene products leads to death, sterility or low hybrid fitness