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A ring species is a species with a counterexample to the transitivity of interbreeding. [3] However, it is unclear whether any of the examples of ring species cited by scientists actually permit gene flow from end to end, with many being debated and contested. [4]
The concept of a ring species is associated with allopatric speciation as a special case; [13] however, Coyne and Orr argue that Mayr's original conception of a ring species does not describe allopatric speciation, "but speciation occurring through the attenuation of gene flow with distance". They contend that ring species provide evidence of ...
In 2012, Cacho and Baum showed that Euphorbia tithymaloides is a ring species, the first example known among the plants. [25] It has reproduced and evolved, spreading in a forked pattern along either side of the Caribbean basin, through Central America and the Caribbean, and meeting again in the Virgin Islands , where the two fronts there ...
As such, it is thought to be an example of incipient speciation, providing an illustration of "nearly all stages in a speciation process" (Dobzhansky, 1958). [2] [7] Richard Highton, zoologist, argued that Ensatina is a genus of multiple species and not a continuum of one (meaning, by traditional definitions, it is not a ring species). [8]
Species with differentiated populations, such as ring species, are sometimes seen as an example of early, ongoing speciation: a species complex in formation. Nevertheless, similar but distinct species have sometimes been isolated for a long time without evolving differences, a phenomenon known as "morphological stasis". [ 19 ]
However, ring species are at best rare. Proposed examples include the herring gull–lesser black-backed gull complex around the North pole, the Ensatina eschscholtzii group of 19 populations of salamanders in America, [108] and the greenish warbler in Asia, [109] but many so-called ring species have turned out to be the result of ...
A niche must be available in order for a new species to be successful. Ring species such as Larus gulls have been claimed to illustrate speciation in progress, though the situation may be more complex. [36] The grass Anthoxanthum odoratum may be starting parapatric speciation in areas of mine contamination. [37]
Many of its species are abundant and well-known birds in their ranges. Until about 2005–2007, most gulls were placed in this genus, but this arrangement is now known to be polyphyletic , leading to the resurrection of the genera Chroicocephalus , Ichthyaetus , Hydrocoloeus , and Leucophaeus for many other species formerly included in Larus .