Ring species
In biology, a ring species is a connected series of neighbouring populations, each of which interbreeds with closely sited related populations, but for which there exist at least two "end populations" in the series, which are too distantly related to interbreed, though there is a potential gene flow between each "linked" population and the next.[1] Such non-breeding, though genetically connected, "end populations" may co-exist in the same region (sympatry) thus closing a "ring". The German term Rassenkreis, meaning a circle of races, is also used.
Ring species represent
Formally, the issue is that
History
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The Larus gulls interbreed in a ring around the arctic. 1:L. vegae, 6: L. smithsonianus, 7: L. argentatus
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Herring gull (Larus argentatus) (front) and lesser black-backed gull (Larus fuscus) (behind) in Norway: twophenotypeswith clear differences
The classic ring species is the
Speciation
The biologist Ernst Mayr championed the concept of ring species, stating that it unequivocally demonstrated the process of speciation.[10] A ring species is an alternative model to allopatric speciation, "illustrating how new species can arise through 'circular overlap', without interruption of gene flow through intervening populations…"[11] However, Jerry Coyne and H. Allen Orr point out that rings species more closely model parapatric speciation.[4]
Ring species often attract the interests of evolutionary biologists, systematists, and researchers of speciation leading to both thought provoking ideas and confusion concerning their definition.[1] Contemporary scholars recognize that examples in nature have proved rare due to various factors such as limitations in taxonomic delineation[12] or, "taxonomic zeal"[10]—explained by the fact that taxonomists classify organisms into "species", while ring species often cannot fit this definition.[1] Other reasons such as gene flow interruption from "vicariate divergence" and fragmented populations due to climate instability have also been cited.[10]
Ring species also present an interesting case of the
Examples
Many examples have been documented in nature. Debate exists concerning much of the research, with some authors citing evidence against their existence entirely.[4][13][self-published source?] The following examples provide evidence that—despite the limited number of concrete, idealized examples in nature—continuums of species do exist and can be found in biological systems.[10] This is often characterized by sub-species level classifications such as clines, ecotypes, complexes, and varieties. Many examples have been disputed by researchers, and equally "many of the [proposed] cases have received very little attention from researchers, making it difficult to assess whether they display the characteristics of ideal ring species."[1]
The following list gives examples of ring species found in nature. Some of the examples such as the Larus gull complex, the greenish warbler of Asia, and the Ensatina salamanders of America, have been disputed.[13][14][15][16]
- Acanthiza pusilla and A. ewingii[17]
- Alauda skylarks (Alauda arvensis, A. japonica and A. gulgula)[1]
- Alophoixus[10][19]
- Aulostomus (Trumpetfish)[20]
- Camarhynchus psittacula and C. pauper[1]
- Chaerephon pumilus species complex[21]
- Ensatina salamanders[22][23]
- Euphorbia tithymaloides is a group within the spurge family that has reproduced and evolved in a ring through Central America and the Caribbean, meeting in the Virgin Islands where they appear to be morphologically and ecologically distinct.[9]
- Great tit[1] (however, some studies dispute this example[24][25])
- The greenish warbler (Phylloscopus trochiloides) forms a species ring, around the Himalayas.[26][27][14] It is thought to have spread from Nepal around the inhospitable Tibetan Plateau, to rejoin in Siberia, where the plumbeitarsus and the viridanus appeared to no longer mutually reproduce.
- Hoplitis producta[1]
- House mouse[1]
- Junonia coenia and J. genoveva/J. evarete[1]
- Lalage leucopygialis, L. nigra, and L. sueurii[1]
- Birula's gull (L. vegae birulai), can hybridize with Heuglin's gull (L. heuglini), which in turn can hybridize with the Siberian lesser black-backed gull (L. fuscus). All four of these live across the north of Siberia. The last is the eastern representative of the lesser black-backed gulls back in north-western Europe, including Great Britain. The lesser black-backed gulls and herring gulls are sufficiently different that they do not normally hybridize; thus the group of gulls forms a continuum except where the two lineages meet in Europe. However, a 2004 genetic study entitled "The herring gull complex is not a ring species" has shown that this example is far more complex than presented here (Liebers et al., 2004):[28] this example only speaks to the complex of species from the classical herring gull through lesser black-backed gull. There are several other taxonomically unclear examples that belong in the same species complex, such as yellow-legged gull (L. michahellis), glaucous gull (L. hyperboreus), and Caspian gull(L. cachinnans).
- Pelophylax nigromaculatus and P. porosus/P. porosus brevipodus[1](the names and classification of these species have changed since the publication suggesting a ring species)
- Pernis ptilorhynchus and P. celebensis[1]
- Perognathus amplus and P. longimembris[1]
- Peromyscus maniculatus[29]
- Phellinus[30]
- Platycercus elegans (Crimson rosella) complex[31][32]
- Drosophila paulistorum[33]
- Phylloscopus collybita and P. sindianus[1]
- Phylloscopus (Willow warblers)[34][35]
- Powelliphanta[36]
- Rhymogona silvatica and R. cervina[1] (the names and classification of these species have changed since the publication suggesting a ring species)
- Melospiza melodia, a Sierra Nevada of California[37] with the subspecies heermanni and fallax meeting in the vicinity of the San Gorgonio Pass.
- Todiramphus chloris and T. cinnamominus[1]
See also
- Dialect continuum, a similar concept in linguistics
- Intergradation
References
- ^ S2CID 7108000.
- ISBN 0-618-00583-8.
- ^ Brown, Rob. "'Same Species' vs. 'Interfertile: concise wording can avoid confusion when discussing evolution".
- ^ ISBN 0-87893-091-4.
- PMID 15255043.
- ^ Irwin, Darren. "The greenish warbler ring species".
- ^ "A closer look at a classic ring species: The work of Tom Devitt". Understanding Evolution. 29 April 2021.
- ^ This species ring forms the subject of "The Salamander's tale" in Richard Dawkins' The Ancestor's Tale, 2004.
- ^ PMID 22696529.
- ^ S2CID 206182763.
- S2CID 29782163.
- PMID 22410355.
- ^ a b Coyne, Jerry (16 July 2014). "There are no ring species". Why Evolution is True.
- ^ S2CID 4458956.
- PMID 15255043.
- JSTOR 3893431.
- ^ Simpson, K.; Day, N.; Trusler, P. (1999), Birds of Australia (6 ed.), Princeton University Press
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- ^ Parmasto, Erast (2007). "Phellinus laevigatus s. l. (Hymenochaetales): a ring species". Folia Cryptogamica Estonica. 43: 39–49.
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