Charles Darwin's first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837)

Speciation is the evolutionary process by which new biological species arise. There are four modes of natural speciation, based on the extent to which speciating populations are geographically isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry or laboratory experiments. Observed examples of each kind of speciation^[1] are provided throughout. Image File history File links Download high resolution version (610x612, 41 KB) Summary Charles Darwins 1837 sketch, his first diagram of an evolutionary tree from his First Notebook on Transmutation of Species (1837) on view at the the Museum of Natural History in Manhattan. ... Image File history File links Download high resolution version (610x612, 41 KB) Summary Charles Darwins 1837 sketch, his first diagram of an evolutionary tree from his First Notebook on Transmutation of Species (1837) on view at the the Museum of Natural History in Manhattan. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... This article is about evolution in biology. ... This article is about evolution in biology. ... In biology, a species is one of the basic units of biodiversity. ... Allopatric speciation, also known as geographic speciation, occurs when populations physically isolated by an extrinsic barrier evolve intrinsic (genetic) reproductive isolation such that if the barrier between the populations breaks down, individuals of the two populations can no longer interbreed. ... Peripatric speciation (also known as Parapatry) is a type of speciation in the theory of natural selection. ... Parapatric speciation is a form of speciation in which the evolution of reproductive isolating mechanisms occurs when a population enters a new niche or habitat within the range of the parent species. ... Sympatry is one of three theoretical models for the phenomenon of speciation. ... In a draw in a mountainous region, a shepherd guides a flock of about 20 sheep amidst scrub and olive trees. ...

Natural speciation

Comparison of allopatric, peripatric, parapatric and sympatric speciation.

All forms of natural speciation have taken place over the course of evolution, though it still remains a subject of debate as to the relative importance of each mechanism in driving biodiversity. ^[2] Image File history File links Speciation_modes. ... Image File history File links Speciation_modes. ... Allopatric speciation, also known as geographic speciation, occurs when populations physically isolated by an extrinsic barrier evolve intrinsic (genetic) reproductive isolation such that if the barrier between the populations breaks down, individuals of the two populations can no longer interbreed. ... Peripatric speciation (also known as Parapatry) is a type of speciation in the theory of natural selection. ... Parapatric speciation is a form of speciation in which the evolution of reproductive isolating mechanisms occurs when a population enters a new niche or habitat within the range of the parent species. ... Sympatry is one of three theoretical models for the phenomenon of speciation. ...

There is debate as to the rate at which speciation events occur over geologic time. While some evolutionary biologists claim that speciation events have remained relatively constant over time, some palaeontologists such as Niles Eldredge and Stephen Jay Gould have argued that species usually remain unchanged over long stretches of time, and that speciation occurs only over relatively brief intervals, a view known as punctuated equilibrium. A paleontologist carefully chips rock from a column of dinosaur vertebrae. ... Dr. Niles Eldredge (born August 25, 1943) is an American paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972. ... It has been suggested that Darwinian Fundamentalism be merged into this article or section. ... Punctuated equilibrium (or punctuated equilibria) is a theory in evolutionary biology which states that most sexually reproducing species will show little to no evolutionary change throughout their history. ...

Allopatric (geographic)

Main article: allopatric speciation

During allopatric speciation, a population splits into two geographically isolated allopatric populations (for example, by habitat fragmentation due to geographical change such as mountain building or social change such as emigration). The isolated populations then undergo genotypic and/or phenotypic divergence as they (a) become subjected to dissimilar selective pressures or (b) they independently undergo genetic drift. When the populations come back into contact, they have evolved such that they are reproductively isolated and are no longer capable of exchanging genes. Allopatric speciation, also known as geographic speciation, occurs when populations physically isolated by an extrinsic barrier evolve intrinsic (genetic) reproductive isolation such that if the barrier between the populations breaks down, individuals of the two populations can no longer interbreed. ... Habitat fragmentation is a process of environmental change important in evolution and conservation biology. ... Mountain building is when mountains develop out of previously lower terrain, or even seas. ... It has been suggested that this article or section be merged with Immigration. ... Selection is hierachically classified into natural and artificial selection. ... In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ...

Observed instances

Island genetics, the tendency of small, isolated genetic pools to produce unusual traits, has been observed in many circumstances, including insular dwarfism and the radical changes among certain famous island chains, like Komodo and Galapagos, the latter having given rise to the modern expression of evolutionary theory, after being observed by Charles Darwin. Perhaps the most famous example of allopatric speciation is Darwin's Galápagos Finches. Species with a small population size are subject to a higher chance of extinction because they are more vulnerable to genetic drift, resulting in stochastic variation in their gene pool, their demography and their environment. ... Insular dwarfism is the process and condition of the reduction in size of large animals - almost always mammals - when their gene pool is limited to a very small environment, primarily islands. ... Komodo is an island of Indonesia, one of the places where the Komodo Dragon can be found in the wild. ... NASA Satellite photo of the Galápagos archipelago. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... Darwins finches (also known as the Galápagos Finches) are 13 or 14 different closely related species of finches Charles Darwin discovered on the Galápagos Islands, 13 reside on the Galápagos Islands, one on the Cocos Islands. ...

Peripatric (mostly geographic)

Main article: peripatric speciation

In peripatric speciation, new species are formed in isolated, small peripheral populations which are prevented from exchanging genes with the main population. It is related to the concept of a founder effect, since small populations often undergo bottlenecks. Genetic drift is often proposed to play a significant role in peripatric speciation. Peripatric speciation (also known as Parapatry) is a type of speciation in the theory of natural selection. ... Simple illustration of founder effect. ... In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ...

Observed instances

• Mayr bird fauna
• The Australian bird Petroica multicolor
• Reproductive isolation occurs in populations of Drosophila subject to population bottlenecking

Type Species Musca funebris Fabricius, 1787 Drosophila is a genus of small flies whose members are often called small fruit flies, or more appropriately vinegar flies, wine flies, pomace flies, grape flies, and picked fruit-flies. ...

Parapatric (somewhat geographic)

Main article: parapatric speciation

In parapatric speciation, the zones of two diverging populations are separate but do overlap. There is only partial separation afforded by geography, so individuals of each species may come in contact or cross the barrier from time to time, but reduced fitness of the heterozygote leads to selection for behaviours or mechanisms which prevent breeding between the two species. Parapatric speciation is a form of speciation in which the evolution of reproductive isolating mechanisms occurs when a population enters a new niche or habitat within the range of the parent species. ... It has been suggested that this article be split into multiple articles accessible from a disambiguation page. ...

Ecologists refer to parapatric and peripatric speciation in terms of ecological niches. A niche must be available in order for a new species to be successful. Two lichenes species on a rock, in two different ecological niches In ecology, a niche is a term describing the relational position of a species or population in an ecosystem. ...

Observed instances

• Ring species
  • The Larus gulls form a ring species around the North Pole.
  • The Ensatina salamanders, which form a ring round the Central Valley in California.
  • The Greenish Warbler (Phylloscopus trochiloides), around the Himalayas.
• the grass Anthoxanthum has been known to undergo parapatric speciation in such cases as mine contamination of an area.

In this diagram, interbreeding populations are represented by coloured blocks. ... Look up gull in Wiktionary, the free dictionary. ... North Pole Scenery When not otherwise qualified, the term North Pole usually refers to the Geographic North Pole – the northernmost point on the surface of the Earth, where the Earths axis of rotation intersects the Earths surface. ... Ensatina eschscholtzii (commonly known by its genus name, Ensatina) is a species of salamander with a range stretching from British Columbia, through Washington, Oregon, across California (where all seven subspecies variations are located), all the way down to Baja in Mexico. ... Families Salamander is the common name applied to approximately 500 amphibian vertebrates with slender bodies, short legs, and long tails (order Caudata or Urodela). ... The California Central Valley The California Central Valley dominates the central portion of the state of California. ... Official language(s) English Capital Sacramento Largest city Los Angeles Area  Ranked 3rd  - Total 158,302 sq mi (410,000 km²)  - Width 250 miles (400 km)  - Length 770 miles (1,240 km)  - % water 4. ... Binomial name Phylloscopus trochiloides (Sundevall, 1837) Subspecies see text The Greenish Warbler, Phylloscopus trochiloides, is a widespread leaf warbler throughout its breeding range in northeast Europe and northern Asia. ... Perspective view of the Himalayas and Mount Everest as seen from space looking south-south-east from over the Tibetan Plateau. ...

Sympatric (non-geographic)

Main article: sympatric speciation

In sympatric speciation, species diverge while inhabiting the same place. Examples of sympatric speciation are found in insects which become dependent on different host plants in the same area. Sympatry is one of three theoretical models for the phenomenon of speciation. ...

Speciation via polyploidy: A diploid cell undergoes failed meiosis, producing diploid gametes, which self-fertilize to produce a tetraploid zygote.

Polyploidy is a mechanism often attributed to causing some speciation events in sympatry. Not all polyploids are reproductively isolated from their parental plants, so an increase in chromosome number may not result in the complete cessation of gene flow between the incipient polyploids and their parental diploids. Image File history File links Polyploidization. ... Polyploidy refers to cells or organisms that contain more than two copies of each of their chromosomes. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... Not to be confused with miosis. ... Gametes, from the ancient Greek γαμετης (spouse), are the specialized germ cells that come together during fertilization (conception) in organisms that reproduce sexually. ... A zygote (Greek: ζυγωτόν) is a cell that is the result of fertilization. ... Polyploidy refers to cells or organisms that contain more than two copies of each of their chromosomes. ... Sympatry is one of three theoretical models for the phenomenon of speciation. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... For other meanings of this term, see gene (disambiguation). ...

Observed instances

Polyploidy is observed in many species of both plant and animal:

• wheat
• Salsify or goatsbeard
• Cichlids of Lake Victoria, Lake Tanganyika and Lake Malawi
• Xenopus laevis, an African toad

Species T. aestivum T. boeoticum T. compactum T. dicoccoides T. dicoccon T. durum T. monococcum T. spelta T. sphaerococcum T. timopheevii References:   ITIS 42236 2002-09-22 For the indie rock group see: Wheat (band). ... Species about 45, including: Tragopogon coloratus Tragopogon crocifolius Tragopogon cupani Tragopogon dubius Tragopogon floccosus Tragopogon gracilis Tragopogon mirabilis Tragopogon mirus Tragopogon miscellus Tragopogon porrifolius Tragopogon pratensis Tragopogon X crantzii Tragopogon X neohybridus The Goatsbeards or Salsifies are the genus Tragopogon of flowering plants within the family Asteraceae. ... Genera Cichlids (pronounced “sick-lids”) are fishes from the family Cichlidae in the order Perciformes. ... Lake Victoria or Victoria Nyanza (also known as Ukerewe and Nalubaale) is one of the Great Lakes of Africa. ... Lake Tanganyika is a large lake in central Africa (3° 20 to 8° 48 South and from 29° 5 to 31° 15 East). ... Lake Malawi, also known as Lake Nyasa, Lake Nyassa, or Lake Niassa after the Yao word for lake (officially called Niassa in Mozambique), is the most southerly lake in the Great African Rift Valley system. ... Binomial name Xenopus laevis Daudin, 1802 The African clawed frog (Xenopus laevis, also known as platanna) is a species of South African aquatic frog of the genus Xenopus. ...

Reinforcement

Reinforcement is the process by which natural selection increases reproductive isolation.^[3] An important concept in evolutionary biology, reproductive isolation is a category of mechanisms that prevent two or more populations from exchanging genes. ...

Reinforcement may occur after two populations of the same species are separated and then come back into contact. If their reproductive isolation was complete, then they will have already developed into two separate incompatible species. If their reproductive isolation is incomplete, then further mating between the populations will produce hybrids, which may or may not be fertile. If the hybrids are infertile, or fertile but less fit than their ancestors, then there will be no further reproductive isolation and speciation has essentially occurred (e.g., as in horses and donkeys.) If the hybrid offspring are more fit than their ancestors, then the populations will merge back into the same species within the area they are in contact. // In biology, hybrid has two meanings. ... Binomial name Equus caballus Linnaeus, 1758 The horse (Equus caballus, sometimes seen as a subspecies of the Wild Horse, Equus ferus caballus) is a large odd-toed ungulate mammal, one of ten modern species of the genus Equus. ... Binomial name Equus asinus Linnaeus, 1758 For other uses, see Donkey (disambiguation). ...

Reinforcement is required for both parapatric and sympatric speciation. Without reinforcement, the geographic area of contact between different forms of the same species, called their "hybrid zone," will not develop into a boundary between the different species. And also without reinforcement they will have uncontrollable interbreeding.

Reinforcement may be induced in artificial selection experiments as described below.

Artificial speciation

New species have been created by domesticated animal husbandry, but the initial dates and methods of the initiation of such species are not clear. For example, domestic sheep were created by hybridisation,^[4] and no longer produce viable offspring with Ovis orientalis, one species from which they are descended.^[5] Domestic cattle on the other hand, can be considered the same species as several varieties of wild ox, gaur, yak, etc., as they willingly and readily reproduce, producing fertile offspring, with several related "other" species.^{[citation needed]} In a draw in a mountainous region, a shepherd guides a flock of about 20 sheep amidst scrub and olive trees. ... Lamb redirects here. ... Binomial name Ovis musimon, Ovis ammon musimon, Ovis orientalis Pallas, 1762 European Mouflon The Mouflon is a species of wild sheep and as such is one of the Caprinae or goat antelopes. It is thought to be one of the two ancestors for all modern domestic sheep breeds[1]. It... Binomial name Bos taurus Linnaeus, 1758 Cattle (often called cows in vernacular and contemporary usage, or kye as the Scots plural of cou) are domesticated ungulates, a member of the subfamily Bovinae of the family Bovidae. ... Binomial name Bos taurus Linnaeus, 1758 Cattle are domesticated ungulates, a member of the subfamily Bovinae of the family Bovidae. ... Binomial name Bos gaurus H. Smith, 1827 The Gaur (IPA gauɹ) (Bos gaurus, previously Bibos gauris) is a large, dark-coated ox of the hilly areas of South Asia and Southeast Asia, which may be found wild or domesticated. ... Binomial name Bos grunniens Linnaeus, 1766 Subspecies Bos grunniens grunniens Bos grunniens mutus The yak (Bos grunniens) is a long-haired humped domestic bovine found in Tibet and throughout the Himalayan region of south central Asia, as well as in Mongolia. ...

The best-documented creations of new species in the laboratory were performed in the late 1980s. Rice and Salt bred fruit flies, Drosophila melanogaster, using a maze with three different choices such as light/dark and wet/dry. Each generation was placed into the maze, and the groups of flies which came out of two of the eight exits were set apart to breed with each other in their respective groups. After thirty-five generations, the two groups and their offspring would not breed with each other even when doing so was their only opportunity to reproduce.^[6] Binomial name Drosophila melanogaster Meigen, 1830 [1] Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order of the flies. ...

Diane Dodd was also able to show allopatric speciation by reproductive isolation in Drosophila pseudoobscura fruit flies after only eight generations using different food types, starch and maltose.^[7] Dodd's experiment has been easy for many others to replicate, including with other kinds of fruit flies and foods.^[8] Allopatric speciation, also known as geographic speciation, occurs when populations physically isolated by an extrinsic barrier evolve intrinsic (genetic) reproductive isolation such that if the barrier between the populations breaks down, individuals of the two populations can no longer interbreed. ... An important concept in evolutionary biology, reproductive isolation is a category of mechanisms that prevent two or more populations from exchanging genes. ...

The Drosophila experiment conducted by Diane Dodd in 1989.

The history of such attempts is described in Rice and Hostert (1993).^[9] Image File history File links Drosophila_speciation_experiment. ... Image File history File links Drosophila_speciation_experiment. ...

Gene transposition as a cause of speciation

Theodosius Dobzhansky, who studied fruit flies in the early days of genetic research in 1930s, speculated that parts of chromosomes that switch from one location to another might cause a species to split into two different species. He mapped out how it might be possible for sections of chromosomes to relocate themselves in a genome. Those mobile sections can cause sterility in inter-species hybrids, which can act as a speciation pressure. In theory, his idea was sound, but scientists long debated whether it actually happened in nature. Eventually a competing theory involving the gradual accumulation of mutations was shown to occur in nature so often that geneticists largely dismissed the moving gene hypothesis.^[10] Theodosius Grigorevich Dobzhansky (Russian — Феодосий Григорьевич Добржанский; sometimes anglicized to Theodore Dobzhansky; January 25, 1900 - December 18, 1975) was a noted geneticist and evolutionary biologist. ... Species Drosophila melanogaster Drosophila subobscura Drosophila is a genus of small flies whose members are often called fruit flies or more appropriately vinegar flies, wine flies, pomace flies, grape flies, and picked fruit-flies. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... This article is about a biological term. ...

However, recent research shows that jumping of a gene from one chromosome to another can contribute to the birth of new species ^[11] This validates reproductive isolation mechanism, a key component of speciation. ^[12]

Interspersed repeats catalyzing speciation

Main article: Interspersed repeat

Interspersed repetitive DNA sequences function as isolating mechanisms. These repeats protect newly evolving gene sequences from being overwritten by gene conversion, due to the creation of non-homologies between otherwise homologous DNA sequences. The non-homologies create barriers to gene conversion. This barrier allows nascent novel genes to evolve without being overwritten by the progenitors of these genes. This uncoupling allows the evolution of new genes, both within gene families and also allelic forms of a gene. The importance is that this allows the splitting of a gene pool without requiring physical isolation of the organisms harboring those gene sequences. Interspersed repetitive DNA is found in all eukaryotic genomes. ... Interspersed repetitive DNA is found in all eukaryotic genomes. ... An important concept in evolutionary biology, reproductive isolation is a category of mechanisms that prevent two or more populations from exchanging genes. ... Gene conversion is a phenomenon which occurs during meiotic division. ... A gene family is a set of genes defined by presumed homology, i. ... For the hard rock band, see Allele (band). ... The gene pool of a species or a population is the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. ...

Koinophilia-driven speciation

Main article: Koinophilia

There are two major evolutionary problems associated with speciation. The first problem is why the process of phenotypic canalization affects the entire external appearance (including behavior), producing phenotypic gaps between species. The second problem is why is speciation so prominent and almost universal among sexual creatures, while often being conspicuously absent among asexual creatures. Asexual organisms very frequently show the continuous variation in form (often in many different directions) that evolution is expected to produce, making their classification into "species" (more correctly "morphospecies") very difficult^{[13][14][15][16]}. Koinophilia is a term used in genetics, meaning that sexual creatures prefer mates with a preponderance of common or average features. ...

Returning to the first problem: during the speciation process the different phenotypic features that make up each individual's appearance are canalized (i.e. made to look the same in all the individuals) regardless of the traits' relative contributions to fitness. Thus, a deer's tail does not contribute nearly as much to the animal's fitness as does its fur coat, the shape of its ears or the position of its eyes, yet all vary as little in form and appearance as do the others, as if selection were acting equally strongly on all of them. (It is a general principle in evolution that features that are neither particularly advantageous, nor disadvantageous, are be expected to be subject to greater individual variation than, say, the camouflage coloring of the coat, which is under strong selective pressure causing it to be the same in all the individuals in the same environment.)

This canalization of the entire phenotype is extraordinary. Consider the wide variety of dogs that humans have bred over the past 100 years or so. There are breeds with no fur at all, and others with exta thick coats; there are long-legged greyhounds and stubby-legged dachshund; there are long snouted collies and stub nosed pugs and bull dogs; and so it goes on - great danes and chihuahuas; loose skinned dogs and tight skinned dogs. That all of these breeds could have been derived in such a short space of time implies that all of this enormous variation was already latently present in the original domestic dog population. This, in turn, implies that evolution has an enormous amount of raw material, on hand, to work with. The slightest change of circumstances would, therefore, be expected to produce a change in phenotype. This is indeed what happens in asexual creatures^[14][15][16]. Sexual creatures, however, seem to vigorously resist these changes, down to even the most trivial of phenotypic features.

This is, however, only one aspect of what is almost certainly a two-dimensional problem. The "horizontal" dimension refers to the almost complete absence of transitional forms between present-day species (e.g. lions, leopards, cheetahs and tigers). The "vertical" dimension concerns the fossil record. Palaeontological species are frequently remarkably stable over extremely long periods of geological time, despite continental drift and major climate changes. When phenotypic change does occur, it tends to be abrupt in geological terms, again producing phenotypic gaps, but now between successive species, which often co-exist for considerable periods of time.

Koinophilia could explain both the horizontal and vertical manifestations of speciation, and why it usually involves the entire external phenotype^[17][13]. Since, by definition, fit traits replace less fit traits, each fit trait tends to become more common, and ultimately the dominant phenotype, while the maladaptive traits become increasingly rare. Sexual creature would therefore be expected to prefer mates sporting predominantly common features, while avoiding mates with unusual or unfamiliar attributes. This is termed koinophilia. It causes common features to become more common still, and at a rate that exceeds that which would be driven by natural selection alone. Since it affects the entire external phenotype, the members of an interbreeding group will soon all begin to look alike (so much so, that the entire species can often be depicted by means of a single illustration in a wild-life guidebook), and noticeably different from other interbreeding groups. Any individual from one interbeeding group who now wanders into another interbreeding group will immediately be recognised as morphologically different, and will, therefore, be discriminated against during the mating season. This koinophilia-induced reproductive isolation might thus be the first crucial step in the development of, ultimately, molecular biological, physiological, behavioural, and anatomical barriers to hybridization, and thus ultimately to the development of full specieshood. Koinophilia will thereafter defend that species phenotype against invasion by unusual or unfamiliar forms (which might arise by immigration or mutation), and thus be a paradigm of punctuated equilibrium (or the "vertical" aspect of the speciation problem. ^[17]). Koinophilia is a term used in genetics, meaning that sexual creatures prefer mates with a preponderance of common or average features. ...

See also

• Heteropatry
• Chronospecies
• Koinophilia

Heteropatry is a concept the refines our notion of sympatry in recognizing that though two variants (genotypes, strains, races) of a population coexist in the same geographical area, these variants are behaviorally separated in terms of exploiting niches that are interwoven to produce a heterogeneous or patchwork landscape. ... A chronospecies is a species which which changes physically, morphologically, genetically, and/or behaviorally over time on an evolutionary scale such that the originating species and the species it becomes could not be classified as the same species had they existed at the same point in time. ... Koinophilia is a term used in genetics, meaning that sexual creatures prefer mates with a preponderance of common or average features. ...

References

External links

• Observed Instances of Speciation from the Talk.Origins Frequently Asked Questions
• Speciation, and
• Evidence for Speciation from Understanding Evolution by the University of California Museum of Paleontology
• Speciation from John Hawks' Anthropology Weblog - paleoanthropology, genetics, and evolution