Do Ring Species Demonstrate Evolution?

Short Answer: At this time, the rings species concept is unable to demonstrate evolution. First, there are no known (proven) examples of ring Species. Even if one were found, it would not by itself support evolution. As both the Creation and Evolution models predict speciation, it would have to be shown the ring formed by evolutionary processes to give support to the Model of Evolution.

An Evolutionary Idea with no Examples

Ring Species are defined as a series of connected populations which spread around a geographic barrier where neighboring populations are able to interbreed but the distant populations that meet after the barrier are unable to interbreed. The basic idea was first suggested in the early 1900's and the concept was formalized in the 1940's. This idea was to show in a spatial dimension what is typically expected of evolution in a time dimension. Only a few species have been suggested as potential Ring Species, but with further study each has been found to not qualify as true Ring Species. Therefore, the Ring Species concept is an evolutionary idea lacking any proven examples.

The Ring Species Concept is defined as a series of connected populations which spread around a geographic barrier where neighboring populations are able to interbreed but the distant populations that meet after the barrier are unable to interbreed. The basic idea was first suggested in the early 1900's and the concept was formalized in the 1940's. This idea was to show in a spatial dimension what is typically expected of evolution in a time dimension. Only a few species have been suggested as potential Ring Species, but with further study each has been found to not qualify as true Ring Species. Therefore, the Ring Species concept is an evolutionary idea lacking any proven examples.

History of the Ring Species Concept

In 1905, David Jordan suggested the basic concepts of what would become known as Ring Species. In 1942, Ernst Mayr solidified the concepts and requirements for what he called 'circular overlaps'. It was not until 1954 that the term 'ring species' was brought out by Arthur Cain. Within this topic of study, the term 'rassenkreis' may be encountered which is the German equivalent for a ring of populations.

Ring Species Characteristics: 1) A species splits into two continuous grades of populations 2) In the shape of a ring (typically surrounding a geographic barrier or unsuitable habitat) 3) Populations acquire new traits as they move away from ancestral home 4) Hybridization and gene flow occur in neighboring populations 5) The two populations where the ends of the ring come together are two distinct, coexisting forms which are unable to interbreed ... In other words using the illustration: an original population splits into two lines - Populations 1,2,3,4 and populations a,b,c,d - where each population overlap can hybridize except Populations P4 and Pd.

Problems Defining a Species There are many difficulties in defining a species and this becomes quite apparent in the concept of Ring Species. If a ring were truly found, the two ends that are unable to interbreed would act like two separate species. Yet, the entire ring, from one end to the other, is able to breed and would therefore be considered one species. Darwin introduced the term 'incipient species' to suggest varieties predicted to become separate in the future. This idea is a large 'what if' as evidence so far has shown suggested ring species merge, rather than diverge, when they come back together - the opposite of what is needed for evolution to occur.

Evolutionary Importance of Gene Flow Most of the time, speciation is considered to occur because of reproductive isolation. Within Ring Species, the possibility of speciation without such isolation would be a great find toward showing Darwinian style evolution as it would create a situation where a single species could become two species, due to divergent populations, even with some connected genetic flow.

Candidates for Ring Species

There have been several suggested candidates for Ring Species. The most notable are the:

1) The Ensatina Salamanders surrounding the Central Valley of California 2) The Larus Gulls near the Arctic Circle 3) The Greenish Warbler surrounding the Tibeten Plateau 4) The Crimson Rosella Parrot in Australia 5) The Caribbean Slipper Spurge in Central America.

What is Really Observed

The major downfall of the Ring Species concept is that the end populations, which by definition cannot interbreed, have been found to interbreed even in the wild, typically with fertile offspring. Therefore the species is only showing some variations (as a subspecies) based on the surrounding environment. It remains the same species. The changes that are observed are referred to as Pre-zygotic Barriers which mean characteristics used in choosing a mating partner rather than Post-zygotic Barriers whose characteristics mean successful fertilization cannot occur even when attempted because of genetic dissimilarity. This is further enhanced by recent DNA studies which conclude that the genetics of each population is typically formed by isolation rather than the necessary continuous gene flow.

Crimson Rosella Parrots are Not Ring Species

The Ring Species Concept was first suggested in 1905 and then later formalized in the 1940's. It suggested that the evolutionary process of speciation could be seen across geographic space by showing that genetic variations of the same species could not interbreed. It was suggested that the Crimson Rosella Parrot surrounding the semi-arid regions of Australia might qualify as a Ring Species. With further study, it was found that interbreeding occurs within all forms and that DNA analysis shows no relationship between geographic location and color which should be found in a Ring Species. Therefore the Crimson Rosella Parrot does not qualify as a Ring Species.

Crimson Rosella Parrots The Crimson Rosella Parrots, taxonomically known as Platycercus elegans, live in Australia. The various populations / sub-species of the parrot were thought to form a circle around the semi-arid regions with the two ends of the circle meeting near the headwaters of the Murray and Murrumbidgee Rives. One variation contains crimson and blue plumage. A second variation replaces some red with bright yellow and is known as the Yellow Rosella. A third variation has a fiery yellow-orange in place of some red coloring on the cheeks and back and is known as the Orange Rosella.

Expected Appearance of Ring Species By definition, there are several basic characteristics that must be matched by a plant or animal to qualify as a Ring Species. The three most prominent characteristics are: 1) a series of connected populations encircling a geographic barrier, 2) continuous gene flow along both branches of the ring, and 3) the end populations must be sufficiently different to prohibit interbreeding where they come together.

Actual Appearance of Platycercus elegans Both mitochondrial and nuclear DNA studies show that the geographic positions of these birds is complex. The areas of similarity and dissimilarity do not match what is expected of Ring Species. In fact, there was no conclusive relationship between DNA, plumage color, and geographic location. Furthermore, it was also noted that interbreeding occurs within all forms.

Conclusion The Crimson Rosella Parrot does not meet either of the two main requirements to be considered a Ring Species.

Ensatina Salamanders are not Ring Species

The Ring Species Concept was first suggested in 1905 and then later formalized in the 1940's. It suggested that the evolutionary process of speciation could be seen across geographic space by showing distant variations of the same animal could not interbreed. In 1949, Robert Stebbins suggested the Ensatina salamanders surrounding the Central Valley of California might qualify as a Ring Species. With further study, it was found that the distant variations do interbreed resulting in fertile offspring and DNA analysis shows genetic isolation rather than the gene flow which is expected in a Ring Species. Therefore, the Ensatina salamanders do not qualify as Ring Species.

Ensatina Salamander Varieties The Ensatina salamanders, taxonomically known as Ensatina eschscholtzii, live in the mountainous regions of California. The various populations / sub-species form a circle around the dry Central Valley of California with the ends meeting in the Palamar Mountains near San Diego. The salamander populations following the coastal mountains have colorings that mimic those of the posonous newts. The populations following the Sierra Mountains have camoflauge style markings.

Expected Appearance of Ring Species By definition, there are several basic characteristics that must be matched by a plant or animal to qualify as a Ring Species. The three most prominent characteristics are: 1) a series of connected populations encircling a geographic barrier, 2) continuous gene flow along both branches of the ring, and 3) the end populations must be sufficiently different to prohibit interbreeding where they come together.

Actual Appearance of Ensatina eschscholtzii While DNA analysis does support a common ancestor for these salamanders, there are sharp genetic breaks around the ring which suggest these groups are somewhat isolated and do not have the necessary gene flow for a Ring Species. Furthermore, the two ends are able to hybridize in the wild and have fertile offspring. Some have suggested they are not well adapted because they lack both mimicry and camoflauge coloring, but the fact remains they do exist.

Conclusion The Ensatina salamander complex does not meet two of the main requirements, gene flow and inability to interbreed, necessary to be considered a Ring Species.

Greenish Warblers are Not Ring Species

The Ring Species Concept was first suggested in 1905 and then later formalized in the 1940's. It suggested that the evolutionary process of speciation could be seen across geographic space by showing distant variations of the same animal could not interbreed. In 1938, Claud Ticehurst suggested that the Greenish Warbler populations surrounding the Tibetan Plateau might qualify as a Ring Species. With further study, it was found that the distant variations do interbreed with fertile offspring and DNA analysis shows genetic isolation rather than the gene flow which is expected in a Ring Species. Therefore, the Greenish Warblers do not qualify as a Ring Species.

Greenish Warbler Varieties The Greenish Warblers of Asia, known taxonomically as Phylloscopus trochiloides, are small insect-eating songbirds which live in the forested regions of northern and central Asia. The various populations surround the high Tibetan Plateau where the two ends or the ring overlap in Siberia. There is some difference in plumage throughout the range, but of more significance is the difference in vocalization in bird songs which changes and becomes more complex as one travels north in either side of the ring.

Expected Appearance of Ring Species By definition, there are several basic characteristics that must be matched by a plant or animal to qualify as a Ring Species. The three most prominent characteristics are: 1) a series of connected populations encircling a geographic barrier, 2) continuous gene flow along both branches of the ring, and 3) the end populations must be sufficiently different to prohibit interbreeding where they come together.

Actual Appearance of Phylloscopus trochiloides Recent DNA analysis has demonstrated sharp breaks between areas which suggests isolation rather than gene flow. The two Siberian sub-species, P.t. plumbeitarsus and P.t. viridanus, have been found to hybridize in the wild resulting in fertile offspring.

Conclusion The Green Warbler complex does not meet two of the necesary requirements for being considered a Ring Species.

Larus Gulls are Not Ring Species

The Ring Species Concept was first suggested in 1905 and then later formalized in the 1940's. It suggested that the evolutionary process of speciation could be seen across geographic space by showing distant variations of the same animal could not interbreed. In 1925, Jonathan Dwight suggested that a circumpolar chain of Larus Gull varieties might qualify as a Ring Species. With further study, it was found that the Larus Gull chain is much more complex than at first assumed and that interbreeding does occur in the wild resulting in fertile offspring. Therefore, the Larus Gulls do not qualify as a Ring Species.

Larus Gull Varieties The Larus Gulls, including Larus argentatus and Larus fuscus varieties, live along the coastlines of North America, Northern Asia, and Northern Europe. The various populations surround the circumpolar regions of the norther latitudes. The suggested ends of the ring includes the Herring Gulls and the Lesser Black-backed Gulls, but the complex probably includes the Yellow Legged Gull, the Glaucous Gull, and the Caspian Gull.

Expected Appearance of Ring Species By definition, there are several basic characteristics that must be matched by a plant or animal to qualify as a Ring Species. The three most prominent characteristics are: 1) a series of connected populations encircling a geographic barrier, 2) continuous gene flow along both branches of the ring, and 3) the end populations must be sufficiently different to prohibit interbreeding where they come together.

Actual Appearance of the Larus Populations Mitochondrial DNA studies show extensive hybridization through much of the different species. Furthermore, the Herring Gull group, including L. argentatus, L. vegae, and L. smithsonianus, are distinct taxa which are not each others closest relatives which would normally be expected in Ring Species. Simple observation of the Herring and Lesser Black-backed Gull show that the hybrids are fertile and with pairings being found in Britain, Ireland, France, and Denmark.

Conclusion The Larus Gull complex does not meet to of the necessary requirements for being considered a Ring Species.

References

Alcaide, M., Scordato, E., Price, T, and Irwin, D. () Genomic divergence in a ring species complex. doi: 10.1038/nature13285

Irwin, D., Irwin, J., and Price, T. (2001) Ring Species as bridges between microevolution and Speciation. Genetica 112-113: 223-243, 2001.

Joseph, L., Dolman, G., Donnellan, S., Saint, K., Berg, M, and Bennett, A. (2008). Where and when does a ring start and end? Testing the ring-species hypothesis in a species complex of Australian parrots. Proceedings of the Royal Society B: Biological Sciences, 2008 275, doi: 10.1098/rspb.2008.0765

Liebers, D., Knijff, P., and Helbig, A. (2004). The herring gull complex is not a ring species. Proceedings of the Royal Society B: Biological Sciences, 2004 271, doi: 10.1098/rspb.2004.2679

Liebers-Helbig, D., Sternkopf, V., Helbig, A., and Knijff, P. (2010). The Herring Gull Complex (Larus argentatus – fuscus – cachinnans) as a Model Group for Recent Holarctic Vertebrate Radiations.

Pereira, R., Monahan, W., and Wake, D. (2011) Predictors for reproductive isolation in a ring species complex following genetic and ecological divergence. Evolutionary Biology 2011, 11:194 doi:10.1186/1471-2148-11-194

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