Printer friendly version can be found HERE

Reproductive Isolating Mechanisms

The biological definition of a species is a group of similar organisms that can interbreed to produce fertile, viable offspring. Some extend this to say that this reproduction must occur under natural, not artificial (e.g., in captivity) situations.

When an ancestral species gives rise to two new species, what determines whether the two new species can reproduce?
Consider the mechanisms that restrict gene flow: reproductive isolating mechanisms.

Prezygotic Isolating Mechanisms prevent the formation of viable zygotes.

  • Ecological Isolation


  • Temporal Isolation


  • Behavioral Isolation


  • Mechanical Isolation


  • Gametic Isolation


    Postzygotic Isolating Mechanisms prevent hybrids from passing on their genes.


  • Hybrid Sterility


  • Hybrid Breakdown



    Hybridization Between Species

    If there is interbreeding between two closely related species, there are several possible outcomes.