Ring Species and Speciation

Heath Blackmon, The University of Texas at Arlington, Arlington, Texas, USA
Jeffery P Demuth, The University of Texas at Arlington, Arlington, Texas, USA

Published online: October 2012

DOI: 10.1002/9780470015902.a0001751.pub3

A ring species is a monophyletic group whose range has extended around a geographic barrier to produce a ring-shaped distribution. The populations that make up the ring should be contiguous and without barriers to gene flow anywhere in the ring except where the terminal populations are sympatric but reproductively isolated from one another. Few, if any of the species that have been described as ring species, actually meet all of these requirements. The best documented example of a species that exhibits all of these traits is the greenish warbler complex (Phylloscopus trochiloides). However, even species like the herring gull complex or Ensatina salamanders that fail to exhibit some of the characteristics of a true ring species offer opportunities to study important evolutionary processes. These species are particularly helpful in understanding how microevolutionary changes can create two unique species, how speciation can occur in spite of gene flow, and how geographic speciation with or without adaptive divergence can occur.

Key Concepts:

  • Few organisms exhibit all of the requirements to be considered a true ring species.
  • Ring species are helpful tools that can be used to help elucidate evolutionary processes.
  • The preponderance of avian and mammal ring species may be an ascertainment bias.

Keywords: speciation; geographic variation; geographic speciation; Ensatina; herring gull; greenish warbler

Figure 1. Distribution of taxa identified by Stebbins (1949), but with ranges based on molecular evidence (Wake, 1997).
Figure 2. Diagrammatic representation of the origin of genetic incompatibility in a ring species. The ancestral population (purple) disperses southwards along both sides of a barrier. A mutation at the A locus occurs on one side of the barrier, whereas a mutation at the B locus occurs on the other side. The frequency of the mutant ‘a’ allele (blue colouration) and ‘b’ allele (red colouration) increases as populations disperse southward. Since ‘a’ and ‘b’ alleles are incompatible, sympatric populations fixed for them do not exchange genes (striped region).
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Related Sub-Topics:

Population Structure and Genetics | Evolution of Species | Evolutionary Ecology | Biogeography and Macroecology
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Article Title: Ring Species and Speciation
 
How to Cite close
Blackmon, Heath, and Demuth, Jeffery P(Oct 2012) Ring Species and Speciation. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001751.pub3]