Parapatric speciation

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Comparison of allopatric, peripatric, parapatric and sympatric speciation.

Parapatric and parapatry are terms from biogeography, referring to organisms whose ranges do not significantly overlap but are immediately adjacent to each other; they only occur together in the narrow contact zone, if at all. Such organisms are usually closely related (e.g. sister species), their distribution being the result of parapatric speciation.

Parapatric speciation is a form of speciation that occurs due to variations in the mating habits of a population within a continuous geographical area. In this model, the parent species lives in a continuous habitat, in contrast with allopatric speciation and peripatric speciation where subpopulations become geographically isolated. Niches in this habitat can differ along an environmental gradient, hampering gene flow, and thus creating a cline.

An example^[1] of this is the grass Anthoxanthum, which has been known to undergo parapatric speciation in such cases as mine contamination of an area. This creates a selection pressure for tolerance to those metals. Flowering time generally changes (in an attempt at character displacement—strong selection against interbreeding—as the hybrids are generally ill-suited to the environment) and often plants will become self-pollinating.

Another example are ring species.

See also

• Allopatry
• Speciation
• Adaptive radiation
• Cladistics
• Evolutionary radiation
• Phylogenetics
• Taxonomy

References

1. ^ "Evolution in closely adjacent plant populations X: long-term persistence of pre-reproductive isolation at a mine boundary." Heredity. 2006 Jul;97(1):33-7. Epub 2006 Apr 26. Abstract.

"Parapatric speciation." in Understanding Evolution at evolution.berkeley.edu