Isolation Barriers

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•  Reproductive isolation of populations can be temporal, behavioural or geographic

Reproductive isolation occurs when barriers prevent two populations from interbreeding – keeping their gene pools separate

There are two main categories of reproductive isolation barriers:

  • Prezygotic isolation – occurs before fertilisation can occur (no offspring are produced)
  • Postzygotic isolation – occurs after fertilisation (offspring are either not viable or infertile)

Prezygotic isolation barriers can be temporal, behavioural, geographic / ecological or mechanical; whereas postzygotic isolation barriers include the inviability, infertility or breakdown of hybrid organisms

Reproductive Isolation Mechanisms

reproductive isolation

Temporal Isolation

  • Temporal isolation occurs when two populations differ in their periods of activity or reproductive cycles
  • Example:  Leopard frogs and wood frogs reach sexual maturity at different times in the spring and hence cannot interbreed

Behavioural Isolation

  • Behavioural isolation occurs when two populations exhibit different specific courtship patterns
  • Example:  Certain populations of crickets may be morphologically identical but only respond to specific mating songs

Geographic Isolation

  • Geographic isolation occurs when two populations occupy different habitats or separate niches within a common region
  • Example:  Lions and tigers occupy different habitats and do not interbreed (usually)

Types of Reproductive Isolation

Isolating mechanisms