Editing Peripatric speciation (section)

== Models ==
=== Peripatric ===
Peripatric speciation models are identical to models of [[vicariance]] (allopatric speciation).<ref name="Speciation"/>{{rp|105}} Requiring both geographic separation and time, speciation can result as a predictable byproduct.<ref>{{Citation |title=Theory and speciation |author=Michael Turelli, Nicholas H. Barton, & Jerry A. Coyne |journal=Trends in Ecology & Evolution |year=2001 |volume=16 |issue=7 |pages=330–343 |doi=10.1016/s0169-5347(01)02177-2|pmid=11403865 }}</ref> Peripatry can be distinguished from allopatric speciation by three key features:<ref name="Speciation"/>{{rp|105}}
*The size of the isolated population
*Strong [[Natural selection|selection]] caused by the dispersal and colonization of novel environments, 
*The effects of [[genetic drift]] on small populations.

The size of a population is important because individuals colonizing a new habitat likely contain only a small sample of the genetic variation of the original population. This promotes divergence due to strong selective pressures, leading to the rapid [[Fixation (population genetics)|fixation]] of an [[allele]] within the descendant population. This gives rise to the potential for genetic incompatibilities to [[evolution|evolve]]. These incompatibilities cause [[reproductive isolation]], giving rise to—sometimes rapid—speciation events.<ref name="Speciation"/>{{rp|105}} Furthermore, two important predictions are invoked, namely that geological or climatic changes cause populations to become locally fragmented (or regionally when considering allopatric speciation), and that an isolated population's reproductive traits evolve enough as to prevent interbreeding upon potential [[secondary contact]].<ref name="ST2007">{{Citation |title=Song divergence at the edge of Amazonia: an empirical test of the peripatric speciation model |author=Nathalie Seddon & Joseph A. Tobias |journal=Biological Journal of the Linnean Society |year=2007 |volume=90 |pages=173–188 |doi=10.1111/j.1095-8312.2007.00753.x|doi-access=free }}</ref>

The peripatric model results in, what have been called, progenitor-derivative species pairs, whereby the derivative species (the peripherally isolated population)—geographically and genetically isolated from the progenitor species—diverges.<ref>{{Citation |title=Progenitor-derivative species pairs and plant speciation |author=Daniel J. Crawford |journal=Taxon |year=2010 |volume=59 |issue=5 |pages=1413–1423 |doi=10.1002/tax.595008 }}</ref> A specific [[Phylogenetics|phylogenetic]] signature results from this mode of speciation: the geographically widespread progenitor species becomes [[paraphyletic]] (thereby becoming a [[paraspecies]]), with respect to the derivative species (the peripheral isolate).<ref name="Speciation"/>{{rp|470}} The concept of a paraspecies is therefore a logical consequence of the [[Species#Evolutionary species|evolutionary species concept]], by which one species gives rise to a daughter species.<ref name="AlbertReis2011">{{cite book|author=James S. Albert & Roberto E. Reis |title=Historical Biogeography of Neotropical Freshwater Fishes |url=https://books.google.com/books?id=V8kZeHxkv9oC&pg=PA316 |isbn=978-0-520-26868-5 |year=2011|publisher=University of California Press }}</ref> It is thought that the character traits of the peripherally isolated species become [[Symplesiomorphy|apomorphic]], while the central population remains [[Symplesiomorphy|plesiomorphic]].<ref name="JKFrey">{{Citation |title=Modes of Peripheral Isolate Formation and Speciation |author=Jennifer K. Frey |journal=Systematic Biology |year=1993 |volume=42 |issue=3 |pages=373–381 |doi=10.1093/sysbio/42.3.373|s2cid=32546573 }}</ref>

Modern cladistic methods have developed definitions that have incidentally removed derivative species by defining clades in a way that assumes that when a speciation event occurs, the original species no longer exists, while two new species arise; this is not the case in peripatric speciation.<ref name="Gottlieb2003"/> Mayr warned against this, as it causes a species to lose their classification status.<ref>{{Citation|title=A local flora and the biological species concept |author=Ernst Mayr |journal=American Journal of Botany |year=1992 |volume=79 |issue=2 |pages=222–238 |doi=10.2307/2445111 |jstor=2445111 }}</ref> Loren H. Rieseberg and Luc Brouillet recognized the same dilemma in plant classification.<ref>{{Citation|title=Are many plant species paraphyletic? |author=Loren H. Rieseberg and Luc Brouillet |journal=Taxon |year=1994 |volume=43 |issue=1 |pages=21–32 |doi=10.2307/1223457 |jstor=1223457 }}</ref>

=== Quantum and budding speciation ===
The botanist Verne Grant proposed the term quantum speciation that combined the ideas of [[J. T. Gulick]] (his observation of the variation of species in semi-isolation), [[Sewall Wright]] (his models of genetic drift), Mayr (both his peripatric and genetic revolution models), and [[George Gaylord Simpson]] (his development of the idea of [[quantum evolution]]).<ref name="Grant1971">{{Citation|title=Plant Speciation |author=Verne Grant |date=1971 |publisher=Columbia University Press |location=New York |isbn=978-0231083263 |pages=432 }}</ref>{{rp|114}} Quantum speciation is a rapid process with large genotypic or phenotypic effects, whereby a new, cross-fertilizing plant species buds off from a larger population as a semi-isolated peripheral population.<ref>{{Citation|title=Speciational trends and the role of species in macroevolution |author=Douglas J. Futuyma |journal=The American Naturalist |year=1989 |volume=134 |issue=2 |pages=318–321 |doi=10.1086/284983 |bibcode=1989ANat..134..318F |s2cid=84541831 }}</ref><ref name="Grant1971"/>{{rp|114}} Inbreeding and genetic drift take place due to the reduced population size, driving changes to the genome that would most likely result in extinction (due to low adaptive value).<ref name="Grant1971"/>{{rp|115}} In rare instances, chromosomal traits with adaptive value may arise, resulting in the origin of a new, derivative species.<ref name="Gottlieb2003">{{Citation|title=Rethinking classic examples of recent speciation in plants |author=L. D. Gottlieb |journal=New Phytologist |year=2003 |volume=161 |pages=71–82 |doi=10.1046/j.1469-8137.2003.00922.x |doi-access=free }}</ref><ref>{{Citation|title=Chromosomal rearrangements and speciation |author=Loren H. Rieseberg |journal=Trends in Ecology & Evolution |year=2001 |volume=16 |issue=7 |pages=351–358 |doi= 10.1016/S0169-5347(01)02187-5 |pmid=11403867}}</ref> Evidence for the occurrence of this type of speciation has been found in several plant species pairs: ''[[Layia discoidea]]'' and ''[[Layia glandulosa|L. glandulosa]]'', ''[[Clarkia lingulata]]'' and ''[[Clarkia biloba|C. biloba]]'', and ''[[Stephanomeria malheurensis]]'' and ''S. exigua'' ssp. ''coronaria''.<ref name="Gottlieb2003"/>

A closely related model of peripatric speciation is called budding speciation—largely applied in the context of plant speciation.<ref name="Anacker&Strauss2013">{{Citation|title=The geography and ecology of plant speciation: range overlap and niche divergence in sister species |author=Brian L. Anacker and Sharon Y. Strauss |journal=Proceedings of the Royal Society B |year=2013 |volume=281 |issue=1778 |pages= 20132980|doi=10.1098/rspb.2013.2980 |pmid=24452025 |pmc=3906944 }}</ref> The budding process, where a new species originates at the margins of an ancestral range, is thought to be common in plants<ref name="Anacker&Strauss2013"/>—especially in progenitor-derivative species pairs.<ref>{{Citation|title=Progenitor-derivative species pairs and plant speciation |author=Daniel J. Crawford |journal=Taxon |year=2010 |volume=59 |issue=5 |pages=1413–1423 |doi= 10.1002/tax.595008}}</ref>

=== Centrifugal speciation ===
William Louis Brown, Jr. proposed an alternative model of peripatric speciation in 1957 called centrifugal speciation. This model contrasts with peripatric speciation by virtue of the origin of the genetic novelty that leads to reproductive isolation.<ref name="Gavrilets">{{Citation |title=Patterns of Parapatric Speciation |author=Sergey Gavrilets, Hai Li, & Michael D. Vose |journal=Evolution |year=2000 |volume=54 |issue=4 |pages=1126–1134 |doi=10.1554/0014-3820(2000)054[1126:pops]2.0.co;2|pmid=11005282 |citeseerx=10.1.1.42.6514 |s2cid=198153997 }}</ref> A population of a species experiences periods of geographic range expansion followed by periods of contraction. During the contraction phase, fragments of the population become isolated as small [[Refugium (population biology)|refugial]] populations on the periphery of the central population. Because of the large size and potentially greater genetic variation within the central population, [[mutation]]s arise more readily. These mutations are left in the isolated peripheral populations, promoting reproductive isolation. Consequently, Brown suggested that during another expansion phase, the central population would overwhelm the peripheral populations, hindering speciation. However, if the species finds a specialized ecological niche, the two may coexist.<ref name="DJH">{{cite book |author=Daniel J. Howard |title=Encyclopedia of Life Sciences |chapter=Speciation: Allopatric |journal=eLS |date=2003 |doi=10.1038/npg.els.0001748|isbn=978-0470016176 }}</ref><ref>{{Citation |title=Centrifugal speciation |author=W. L. Brown Jr. |journal=Quarterly Review of Biology |year=1957 |volume=32 |issue=3 |pages=247–277 |doi=10.1086/401875|s2cid=225071133 }}</ref> The phylogenetic signature of this model is that the central population becomes [[Synapomorphy|derived]], while the peripheral isolates stay plesiomorphic<ref name="JKFrey" />—the reverse of the general model. In contrast to centrifugal speciation, peripatric speciation has sometimes been referred to as '''centripetal speciation''' (see figures 1 and 2 for a contrast).<ref>{{Citation |title=Interview with John C. Briggs, recipient of the 2005 Alfred Russel Wallace award |url=https://escholarship.org/uc/item/8jg516kj |author=Brian W. Bowen |journal=Frontiers of Biogeography |year=2010 |volume=2 |issue=3 |pages=78–80 |issn=1948-6596 }}</ref> Centrifugal speciation has been largely ignored in the scientific literature, often dominated by the traditional model of peripatric speciation.<ref name="Briggs">{{Citation |title=Centrifugal speciation and centres of origin |author=John C. Briggs |journal=Journal of Biogeography |year=2000 |volume=27 |issue=5 |pages=1183–1188 |doi=10.1046/j.1365-2699.2000.00459.x|bibcode=2000JBiog..27.1183B |s2cid=86734208 }}</ref><ref name="Gavrilets" /><ref name="JKFrey" /> Despite this, Brown cited a wealth of evidence to support his model, of which has not yet been refuted.<ref name="DJH" />

''[[Peromyscus]] polionotus'' and ''P. melanotis'' (the peripherally isolated species from the central population of ''P. maniculatus'') arose via the centrifugal speciation model.<ref>{{Citation |title=Chromosomal Evolution and the Mode of Speciation in Three Species of Peromyscus |author=Ira F. Greenbaum, Robert J. Baker & Paul R. Ramsey |journal=Evolution |year=1978 |volume=32 |issue=3 |pages=646–654 |pmid=28567964 |doi=10.1111/j.1558-5646.1978.tb04609.x |s2cid=27865356 |doi-access=free }}</ref> Centrifugal speciation may have taken place in [[tree kangaroo]]s, South American frogs (''[[Ceratophrys]]''), shrews (''[[Crocidura]]''), and primates (''[[Sumatran surili|Presbytis melalophos]]'').<ref name="Briggs" /> [[John C. Briggs]] associates centrifugal speciation with [[Center of origin|centers of origin]], contending that the centrifugal model is better supported by the data, citing species patterns from the proposed 'center of origin' within the [[Indo-Pacific|Indo-West Pacific]]<ref name="Briggs" />

=== Kaneshiro model ===
[[File:Kaneshiro Peripatric Speciation (process).png|right|thumb|upright=1.4|In the Kaneshiro model, a sample of a larger population results in an isolated population with fewer males that are able to lower the threshold of receptivity among females. Over time, choosy females are selected against and there is an increase in frequency of less choosy females resulting in a shift in the gene frequency of the population. Such a condition result in a "destabilized" genetic condition allowing new genetic variants to arise. Novel variants that are better adapted to the new habitat will be selected and over time the genetic makeup of the peripatric population may be different enough to become reproductively isolated from the old one.]] 
The Kaneshiro Model also provides an explanation of the mechanism of speciation during founder events as proposed by Ernst Mayr and Hampton Carson. In most cases, founder events result when single fertilized female is accidentally translocated to an entirely different location, e.g., an adjacent island among a chain of islands such as the Hawaiian Archipelago, and produces a few offspring. Such a founder colony is faced with extremely small population size which as described by the Kaneshiro Model, experiences a shift in the mating system towards and increase in frequency of less choosy females. The resulting destabilization of the genetic system provides the milieu for new genetic variants to arise providing the recipe for speciation to occur. Eventually, a growth in population size paired with novel [[Mating preferences#Female mate preferences|female mate preferences]] will give rise to reproductive isolation from the main population-thereby completing the speciation process.<ref name=KYK1980/> Support for this model comes from experiments and observation of species that exhibit asymmetric mating patterns such as the [[Hawaiian Drosophila|Hawaiian ''Drosophila'']] species<ref>{{Citation |title=Sexual selection and direction of evolution in the biosystematics of Hawaiian Drosophilidae |author=Kenneth Y. Kaneshiro |journal=Annual Review of Entomology |year=1983 |volume=28 |pages=161–178 |doi=10.1146/annurev.en.28.010183.001113}}</ref><ref>{{Citation |title=Behavioral Phylogenies and the Direction of Evolution |author=Luther Val Giddings & Alan R. Templeton |journal=Science |year=1983 |volume=220 |issue=4595 |pages=372–378 |doi=10.1126/science.220.4595.372 |pmid=17831399 |bibcode=1983Sci...220..372G |s2cid=45100702 }}</ref> or the Hawaiian cricket ''[[Laupala]]''.<ref>{{Citation |title=Mating asymmetry and the direction of evolution in the Hawaiian cricket genus ''Laupala'' |author=Kerry L. Shaw & Ezequiel Lugo |journal=Molecular Ecology |year=2001 |volume=10 |issue=3 |pages=751–759 |doi=10.1046/j.1365-294x.2001.01219.x |pmid=11298985 |bibcode=2001MolEc..10..751S |s2cid=38590572 }}</ref> However, while laboratory experiments are ongoing and yet to be completed in support of the model, there are field observations of shifts in the mating systems that undergo population bottlenecks which demonstrate that the dynamics of sexual selection is occurring in nature and therefore, it does represent a plausible process of peripatric speciation that takes place in nature.<ref name=AO&ABF2002/>