Peripatric speciation is a mode ofspeciation in which a newspecies is formed from an isolated peripheral population.[1]: 105 Since peripatric speciation resemblesallopatric speciation, in that populations are isolated and prevented fromexchanging genes, it can often be difficult to distinguish between them,[2] and peripatric speciation may be considered one type ormodel of allopatric speciation.[3] The primary distinguishing characteristic of peripatric speciation is that one of the populations is much smaller than the other, as opposed to (other types of) allopatric speciation, in which similarly-sized populations become separated. The termsperipatric andperipatry are often used inbiogeography, referring toorganisms whose ranges are closely adjacent but do not overlap, being separated where these organisms do not occur—for example on anoceanic island compared to the mainland. Such organisms are usually closely related (e.g.sister species); their distribution being the result of peripatric speciation.
The concept of peripatric speciation was first outlined by the evolutionary biologistErnst Mayr in 1954.[4] Since then, other alternative models have been developed such ascentrifugal speciation, that posits that a species' population experiences periods of geographicrange expansion followed by shrinking periods, leaving behind small isolated populations on the periphery of the main population. Other models have involved the effects ofsexual selection on limited population sizes. Other related models of peripherally isolated populations based on chromosomal rearrangements have been developed such asbudding speciation andquantum speciation.
The existence of peripatric speciation is supported by observational evidence and laboratory experiments.[1]: 106 Scientists observing the patterns of a species biogeographic distribution and itsphylogenetic relationships are able to reconstruct the historical process by which theydiverged. Further, oceanic islands are often the subject of peripatric speciation research due to their isolated habitats—with theHawaiian Islands widely represented in much of the scientific literature.
Peripatric speciation was originally proposed byErnst Mayr in 1954,[4] and fully theoretically modeled in 1982.[5] It is related to thefounder effect, where small living populations may undergo selection bottlenecks.[6] The founder effect is based on models that suggest peripatric speciation can occur by the interaction of selection andgenetic drift,[1]: 106 which may play a significant role.[7] Mayr first conceived of the idea by his observations ofkingfisher populations in New Guinea and its surrounding islands.[1]: 389 Tanysiptera galatea was largely uniform in morphology on the mainland, but the populations on the surrounding islands differed significantly—referring to this pattern as "peripatric".[1]: 389 This same pattern was observed by many of Mayr's contemporaries at the time such as byE. B. Ford's studies ofManiola jurtina.[8]: 522 Around the same time, the botanistVerne Grant developed a model of quantum speciation very similar to Mayr's model in the context of plants.[9]
In what has been called Mayr's genetic revolutions, he postulated that genetic drift played the primary role that resulted in this pattern.[1]: 389 Seeing that a species cohesion is maintained by conservative forces such asepistasis and the slow pace of the spread of favorable alleles in a large population (based heavily onJ. B. S. Haldane's calculations), he reasoned that speciation could only take place in which apopulation bottleneck occurred.[1]: 389 A small, isolated, founder population could be established on an island for example. Containing less genetic variation from the main population, shifts in allele frequencies may occur from different selection pressures.[1]: 390 This to further changes in the network of linked loci, driving a cascade of genetic change, or a "genetic revolution"—a large-scale reorganization of the entire genome of the peripheral population.[1]: 391 Mayr did recognize that the chances of success were incredibly low and that extinction was likely; though noting that some examples of successful founder populations existed at the time.[8]: 522
Shortly after Mayr, William Louis Brown, Jr. proposed an alternative model of peripatric speciation in 1957 called centrifugal speciation. In 1976 and 1980, the Kaneshiro model of peripatric speciation was developed byKenneth Y. Kaneshiro which focused on sexual selection as a driver for speciation during population bottlenecks.[10][11][12]
Peripatric speciation models are identical to models ofvicariance (allopatric speciation).[1]: 105 Requiring both geographic separation and time, speciation can result as a predictable byproduct.[13] Peripatry can be distinguished from allopatric speciation by three key features:[1]: 105
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 rapidfixation of anallele within the descendant population. This gives rise to the potential for genetic incompatibilities toevolve. These incompatibilities causereproductive isolation, giving rise to—sometimes rapid—speciation events.[1]: 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 potentialsecondary contact.[14]
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.[15] A specificphylogenetic signature results from this mode of speciation: the geographically widespread progenitor species becomesparaphyletic (thereby becoming aparaspecies), with respect to the derivative species (the peripheral isolate).[1]: 470 The concept of a paraspecies is therefore a logical consequence of theevolutionary species concept, by which one species gives rise to a daughter species.[16] It is thought that the character traits of the peripherally isolated species becomeapomorphic, while the central population remainsplesiomorphic.[17]
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.[9] Mayr warned against this, as it causes a species to lose their classification status.[18] Loren H. Rieseberg and Luc Brouillet recognized the same dilemma in plant classification.[19]
The botanist Verne Grant proposed the term quantum speciation that combined the ideas ofJ. 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), andGeorge Gaylord Simpson (his development of the idea ofquantum evolution).[20]: 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.[21][20]: 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).[20]: 115 In rare instances, chromosomal traits with adaptive value may arise, resulting in the origin of a new, derivative species.[9][22] Evidence for the occurrence of this type of speciation has been found in several plant species pairs:Layia discoidea andL. glandulosa,Clarkia lingulata andC. biloba, andStephanomeria malheurensis andS. exigua ssp.coronaria.[9]
A closely related model of peripatric speciation is called budding speciation—largely applied in the context of plant speciation.[23] The budding process, where a new species originates at the margins of an ancestral range, is thought to be common in plants[23]—especially in progenitor-derivative species pairs.[24]
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.[25] 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 smallrefugial populations on the periphery of the central population. Because of the large size and potentially greater genetic variation within the central population,mutations 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.[26][27] The phylogenetic signature of this model is that the central population becomesderived, while the peripheral isolates stay plesiomorphic[17]—the reverse of the general model. In contrast to centrifugal speciation, peripatric speciation has sometimes been referred to ascentripetal speciation (see figures 1 and 2 for a contrast).[28] Centrifugal speciation has been largely ignored in the scientific literature, often dominated by the traditional model of peripatric speciation.[29][25][17] Despite this, Brown cited a wealth of evidence to support his model, of which has not yet been refuted.[26]
Peromyscus polionotus andP. melanotis (the peripherally isolated species from the central population ofP. maniculatus) arose via the centrifugal speciation model.[30] Centrifugal speciation may have taken place intree kangaroos, South American frogs (Ceratophrys), shrews (Crocidura), and primates (Presbytis melalophos).[29]John C. Briggs associates centrifugal speciation withcenters of origin, contending that the centrifugal model is better supported by the data, citing species patterns from the proposed 'center of origin' within theIndo-West Pacific[29]
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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 novelfemale mate preferences will give rise to reproductive isolation from the main population-thereby completing the speciation process.[11] Support for this model comes from experiments and observation of species that exhibit asymmetric mating patterns such as theHawaiianDrosophila species[31][32] or the Hawaiian cricketLaupala.[33] 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.[12]
Observational evidence and laboratory experiments support the occurrence of peripatric speciation.Islands andarchipelagos are often the subject of speciation studies in that they represent isolated populations of organisms. Island species provide direct evidence of speciation occurring peripatrically in such that, "the presence ofendemic species on oceanic islands whose closest relatives inhabit a nearbycontinent" must have originated by a colonization event.[1]: 106–107 Comparativephylogeography of oceanicarchipelagos shows consistent patterns of sequential colonization and speciation along island chains, most notably on theAzores islands,Canary Islands,Society Islands,Marquesas Islands,Galápagos Islands,Austral Islands, and the Hawaiian Islands—all of which express geological patterns of spatial isolation and, in some cases, linear arrangement.[34] Peripatric speciation also occurs on continents, as isolation of small populations can occur through various geographic anddispersion events. Laboratory studies have been conducted where populations ofDrosophila, for example, are separated from one another and evolve in reproductive isolation.
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Drosophila species on theHawaiian archipelago have helped researchers understand speciation processes in great detail. It is well established thatDrosophila has undergone anadaptive radiation into hundreds ofendemic species on the Hawaiian island chain;[1]: 107 [35] originating from a single common ancestor (supported from molecular analysis).[36] Studies consistently find that colonization of each island occurred from older to younger islands, and inDrosophila, speciating peripatrically at least fifty percent of the time.[1]: 108 In conjunction withDrosophila, Hawaiian lobeliads (Cyanea) have also undergone an adaptive radiation, with upwards of twenty-seven percent ofextant species arising after new island colonization—exemplifying peripatric speciation—once again, occurring in the old-to-young island direction.[37][38][39]
Other endemic species in Hawaii also provide evidence of peripatric speciation such as the endemic flightless crickets (Laupala). It has been estimated that, "17 species out of 36 well-studied cases of [Laupala] speciation were peripatric".[1]: 108 [40] Plant species in genera's such asDubautia,Wilkesia, andArgyroxiphium have also radiated along the archipelago.[41] Other animals besides insects show this same pattern such as the Hawaiian amber snail (Succinea caduca),[42] andʻElepaio flycatchers.[43]
Tetragnatha spiders have also speciated peripatrically on the Hawaiian islands,[44][45] Numerous arthropods have been documented existing in patterns consistent with the geologic evolution of the island chain, in such that, phylogenetic reconstructions find younger species inhabiting the geologically younger islands and older species inhabiting the older islands[46] (or in some cases, ancestors date back to when islands currently below sea level were exposed). Spiders such as those from the genusOrsonwelles exhibit patterns compatible with the old-to-young geology.[47] Other endemic genera such asArgyrodes have been shown to have speciated along the island chain.[48]Pagiopalus,Pedinopistha, and part of the familyThomisidae have adaptively radiated along the island chain,[49] as well as the wolf spider family,Lycosidae.[50]
A host of other Hawaiian endemic arthropod species and genera have had their speciation and phylogeographical patterns studied: theDrosophila grimshawi species complex,[51]damselflies (Megalagrion xanthomelas andMegalagrion pacificum),[52]Doryonychus raptor,Littorophiloscia hawaiiensis,Anax strenuus,Nesogonia blackburni,Theridion grallator,[53]Vanessa tameamea,Hyalopeplus pellucidus,Coleotichus blackburniae,Labula,Hawaiioscia,Banza (in the familyTettigoniidae),Caconemobius,Eupethicea,Ptycta,Megalagrion,Prognathogryllus,Nesosydne,Cephalops,Trupanea, and the tribePlatynini—all suggesting repeated radiations among the islands.[54]
Phylogenetic studies of a species of crab spider (Misumenops rapaensis) in the genusThomisidae located on theAustral Islands have established the, "sequential colonization of [the] lineage down the Austral archipelago toward younger islands".M. rapaensis has been traditionally thought of as a single species; whereas this particular study found distinct genetic differences corresponding to the sequential age of the islands.[55] Thefigwart plant speciesScrophularia lowei is thought to have arisen through a peripatric speciation event, with the more widespread mainland species,Scrophularia arguta dispersing to theMacaronesian islands.[56][57] Other members of the same genus have also arisen by single colonization events between the islands.[58][59]
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The occurrence of peripatry on continents is more difficult to detect due to the possibility of vicariant explanations being equally likely.[1]: 110 However, studies concerning the Californian plant speciesClarkia biloba andC. lingulata strongly suggest a peripatric origin.[60] In addition, a great deal of research has been conducted on several species of land snails involvingchirality that suggests peripatry (with some authors noting other possible interpretations).[1]: 111
Thechestnut-tailed antbird (Sciaphylax hemimelaena) is located within theNoel Kempff Mercado National Park (Serrania de Huanchaca) in Bolivia. Within this region exists a forest fragment estimated to have been isolated for 1000–3000 years. The population ofS. hemimelaena antbirds that reside in the isolated patch express significant song divergence; thought to be an "early step" in the process of peripatric speciation. Further, peripheral isolation "may partly explain the dramatic diversification ofsuboscines inAmazonia".[14]
The montane spiny throated reed frogspecies complex (genus:Hyperolius) originated through occurrences of peripatric speciation events. Lucinda P. Lawson maintains that the species' geographic ranges within the EasternAfromontane Biodiversity Hotspot support a peripatric model that is driving speciation; suggesting that this mode of speciation may play a significant role in "highly fragmented ecosystems".[2]
In a study of the phylogeny and biogeography of the land snail genusMonacha, the speciesM. ciscaucasica is thought to have speciated peripatrically from a population ofM. roseni. In addition,M. claussi consists of a small population located on the peripheral of the much larger range ofM. subcarthusiana suggesting that it also arose by peripatric speciation.[61]
Red spruce (Picea rubens) has arisen from an isolated population of black spruce (Picea mariana). During thePleistocene, a population of black spruce became geographically isolated, likely due toglaciation. The geographic range of the black spruce is much larger than the red spruce. The red spruce has significantly lower genetic diversity in both its DNA and itsmitochondrial DNA than the black spruce.[62][63] Furthermore, the genetic variation of the red spruce has no unique mitochondrialhaplotypes, only subsets of those in the black spruce; suggesting that the red spruce speciated peripatrically from the black spruce population.[64][65][66] It is thought that the entire genusPicea in North America has diversified by the process of peripatric speciation, as numerous pairs of closely related species in the genus have smaller southern population ranges; and those with overlapping ranges often exhibit weak reproductive isolation.[67][63]
Using a phylogeographic approach paired withecological niche models (i.e. prediction and identification of expansion and contraction species ranges into suitable habitats based on currentecological niches, correlated with fossil and molecular data), researchers found that theprairie dog speciesCynomys mexicanus speciated peripatrically fromCynomys ludovicianus approximately 230,000 years ago. North American glacial cycles promoted range expansion and contraction of the prairie dogs, leading to the isolation of a relic population in arefugium located in the present dayCoahuila, Mexico.[68] This distribution andpaleobiogeographic pattern correlates with other species expressing similar biographic range patterns[68] such as with theSorex cinereus complex.[69]
| Species | Replicates | Year |
|---|---|---|
| Drosophila adiastola | 1 | 1979[70] |
| Drosophila silvestris | 1 | 1980[71] |
| Drosophila pseudoobscura | 8 | 1985[72] |
| Drosophila simulans | 8 | 1985[73] |
| Musca domestica | 6 | 1991[74] |
| Drosophila pseudoobscura | 42 | 1993[75] |
| Drosophila melanogaster | 50 | 1998[76] |
| Drosophila melanogaster | 19; 19 | 1999[77] |
| Drosophila grimshawi | 1 | N/A[12] |
Peripatric speciation has been researched in both laboratory studies and nature.Jerry Coyne andH. Allen Orr inSpeciation suggest that most laboratory studies of allopatric speciation are also examples of peripatric speciation due to their small population sizes and the inevitable divergent selection that they undergo.[1]: 106 Much of the laboratory research concerning peripatry is inextricably linked tofounder effect research. Coyne and Orr conclude that selection's role in speciation is well established, whereasgenetic drift's role is unsupported by experimental and field data—suggesting that founder-effect speciation does not occur.[1]: 410 Nevertheless, a great deal of research has been conducted on the matter, and one study conducted involvingbottleneck populations ofDrosophila pseudoobscura found evidence of isolation after a single bottleneck.[78][79]
The table is a non-exhaustive table of laboratory experiments focused explicitly on peripatric speciation. Most of the studies also conducted experiments on vicariant speciation as well. The "replicates" column signifies the number of lines used in the experiment—that is, how many independent populations were used (not the population size or the number of generations performed).[12]
This article was submitted toWikiJournal of Science for externalacademic peer review in 2018 (reviewer reports). The updated content was reintegrated into the Wikipedia page under aCC-BY-SA-3.0 license (2018). The version of record as reviewed is:Andrew Z Colvin; et al. (14 August 2018)."Peripatric speciation"(PDF).WikiJournal of Science.1 (2): 008.doi:10.15347/WJS/2018.008.ISSN 2470-6345.Wikidata Q56553060.
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