Isolation Mechanisms

Prerequisite for the emergence of species

In reproductive isolation, there is no more gene flow through one or more reproductive barriers. Reproductive barriers can have an intraspecific, but also extra-species effect and permanently lead to the emergence of a new species (exception: isolation by sterility).

 Temporal isolation: Species can not reproduce each other because they reproduce during different seasons / times of the day (for example, frog species whose mating time is in different months).

 Genetic Isolation: By chance mutations individuals can no longer be reproductive with the original population.

 Physiological Isolation: Due to the different shape of the copulatory organs, certain species can not reproduce with each other (for example in closely related insect species).

 Ecological isolation: exploiting different ecological niches in the same area results in reproductive isolation (e.g., Darwin's finches occupying different ecological niches, some individuals feeding on insects, others on grains).

 Geographical Isolation: Because of geographic barriers, sub-populations of a species can not reproduce among themselves (e.g., by continental drift or sea-level rise).

 Behavior Isolation: Different behaviors during the mating season isolate species from each other (for example, closely related species of birds that mate at the same time have a different courtship call).

 Sterility: Hybridization of two unrelated species may produce bastards with an odd set of chromosomes that are not fertile. (For example, in a donkey-and-horse cross, the offspring are all infertile because they have an odd set of chromosomes that make gamete impossible).

 Polyploidy: Polyploidy means the presence of more than two sets of chromosomes. Reproduction is only possible among individuals with an identical number of sets of chromosomes. (For example, plants often form triploid or tetraploid chromosome sets and are thus genetically isolated from their native haploid chromosome set).

Summary

Reproductive isolation prevents gene flow between two or more populations or one or more individuals with a population.

Examples of isolation mechanisms are: temporal, physiological, ecological, geographic, behavioral and genetic isolation.