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Speciation is the evolutionary process by which new biological species arise. Foundations of modern biology There are five unifying principles eVolution is the third Album by eLDee, it was due to be released in 2008 An adaptation is a characteristic of an Organism that has been favored by Natural selection and In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time In Population genetics, gene flow (also known as gene migration) is the transfer of Alleles of Genes from one Population to another In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of The wide range of evidence of common descent of living things strongly indicates the occurrence of Evolution and provides a wealth of information on the natural processes Although evidence of early Life is scarce and often difficult to interpret it appears that life appeared on Earth relatively soon (on the Geologic time scale) after Evolutionary thought, the idea that species change over time has roots in antiquity in the ideas of the Greeks, Romans, Chinese and Muslims theory of transmutation had early origins in the speculations and hypotheses of Erasmus Darwin, and Jean-Baptiste Lamarck. Objections to evolution have been raised ever since various evolutionary ideas came to prominence around the start of the nineteenth century Cladistics is the hierarchical classification of Species based on evolutionary ancestry Ecological genetics is the study of Genetics in the context of the interactions among organisms and between the organisms and their environment Evolutionary developmental biology ( evolution of development or informally evo-devo) is a field of Biology that compares the developmental processes Human evolution, or anthropogenesis, is the part of biological Evolution concerning the emergence of Homo sapiens as a distinct Species Molecular evolution is the process of evolution at the scale of DNA, RNA, and Proteins Molecular evolution emerged as a scientific field in the 1960s as Population genetics is the study of the Allele frequency distribution and change under the influence of the four evolutionary forces Natural selection, Genetic eVolution is the third Album by eLDee, it was due to be released in 2008 In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. 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. Allopatric speciation, also known as geographic Speciation, is the phenomenon whereby biological populations are physically isolated by an extrinsic barrier Peripatric speciation is a form of Speciation, the formation of new Species through Evolution. Parapatric speciation is a form of Speciation that occurs due to variations in mating frequency of a population within a continuous geographical area Sympatric speciation is the genetic divergence of various populations (from a single parent species inhabiting the same geographic region such that those populations become different Speciation may also be induced artificially, through animal husbandry or laboratory experiments. Animal husbandry, also called Animal science, stockbreeding or simple husbandry, is the agricultural practice of breeding Observed examples of each kind of speciation are provided throughout. ^[1]

Natural 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]

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. Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. Niles Eldredge (born August 25 1943 is an American paleontologist, who along with Stephen Jay Gould, proposed the theory of Punctuated equilibrium Stephen Jay Gould (September 10 1941 &ndash May 20 2002 was a prominent American paleontologist, evolutionary biologist, and historian of science Punctuated equilibrium is a theory of evolutionary biology which states that most sexually reproducing populations experience little change for most of their geological

Allopatric

Comparison of allopatric, peripatric, parapatric and sympatric speciation. Allopatric speciation, also known as geographic Speciation, is the phenomenon whereby biological populations are physically isolated by an extrinsic barrier Peripatric speciation is a form of Speciation, the formation of new Species through Evolution. Parapatric speciation is a form of Speciation that occurs due to variations in mating frequency of a population within a continuous geographical area Sympatric speciation is the genetic divergence of various populations (from a single parent species inhabiting the same geographic region such that those populations become different

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). Allopatric speciation, also known as geographic Speciation, is the phenomenon whereby biological populations are physically isolated by an extrinsic barrier Habitat fragmentation is a process of environmental change important in Evolution and Conservation biology. Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and "Emigrant" redirects here For the Butterflies, see Catopsilia. 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. In the context of Evolution, certain traits or Alleles of a Species may be subject to selection In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time When the populations come back into contact, they have evolved such that they are reproductively isolated and are no longer capable of exchanging genes.

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 Galápagos, the latter having given rise to the modern expression of evolutionary theory, after being observed by Charles Darwin. Populations with small population size behave differently to larger populations 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 Komodo is one of the 17508 islands that make up the Republic of Indonesia. Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life Perhaps the most famous example of allopatric speciation is Darwin's Galápagos Finches. Darwin's finches (also known as the Galápagos Finches) are 13 or 14 different closely related Species of Finches that Charles Darwin collected

Peripatric

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. Peripatric speciation is a form of Speciation, the formation of new Species through Evolution. It is related to the concept of a founder effect, since small populations often undergo bottlenecks. In Population genetics, the founder effect refers to the loss of genetic variation when a new colony is established by a very small number of individuals from a larger Genetic drift is often proposed to play a significant role in peripatric speciation. In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time

Observed instances

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

The London Underground mosquito is a variant of the mosquito Culex pipiens which entered in the London Underground in the nineteenth century. The Scarlet Robin ( Petroica boodang) is a common red-breasted Australasian robin in the Passerine Bird Genus Petroica Drosophila is a Genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" The London Underground mosquito is a species of Mosquito in the genus Culex found in the London Underground. The London Underground is a Metro system serving a large part of Greater London and neighbouring areas of Essex, Hertfordshire and Buckinghamshire Evidence for its speciation include genetic divergence, behavioral differences, and difficulty in mating. ^[3]

Parapatric

Main article: parapatric speciation

In parapatric speciation, the zones of two diverging populations are separate but do overlap. Parapatric speciation is a form of Speciation that occurs due to variations in mating frequency of a population within a continuous geographical area 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. Zygosity refers to the genetic condition of a Zygote. In genetics zygosity describes the similarity or dissimilarity of DNA between Homologous

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. In Ecology, a niche (pronounced nich nēsh or nish A shorthand definition of niche is how an organism makes a living

Observed instances

• Ring species
  • The Larus gulls form a ring species around the North Pole. In Biology, a ring species is a connected series of neighboring populations that can interbreed with relatively closely related populations but for which there exist at least Gulls (often informally Seagulls) are birds in the family Laridae The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is subject to the caveats explained below defined as the point in the northern
  • The Ensatina salamanders, which form a ring round the Central Valley in California. Ensatina eschscholtzii (commonly known by its genus name Ensatina) is a species of Salamander with a range stretching from British Salamander (orig from Persian: sām, "fire" and andarūn, "within" is the common name for a group of approximately 500 Species The Central Valley is a large flat valley that dominates the central portion of the U California ( is a US state on the West Coast of the United States, along the Pacific Ocean.
  • The Greenish Warbler (Phylloscopus trochiloides), around the Himalayas. The Greenish Warbler, Phylloscopus trochiloides, is a widespread Leaf-warbler throughout its breeding range in northeast Europe and northern
• the grass Anthoxanthum has been known to undergo parapatric speciation in such cases as mine contamination of an area.

Sympatric

Main article: sympatric speciation

In sympatric speciation, species diverge while inhabiting the same place. Sympatric speciation is the genetic divergence of various populations (from a single parent species inhabiting the same geographic region such that those populations become different Often cited examples of sympatric speciation are found in insects which become dependent on different host plants in the same area. In Biology, a host is an organism that harbors a Virus or Parasite, or a mutual or Commensal Symbiont, typically providing nourishment However, the existence of sympatric speciation as a mechanism of speciation is still hotly contested. People have argued that the evidences of sympatric speciation are in fact examples of micro-allopatric, or heteropatric speciation. Heteropatric speciation is a special case of Sympatric speciation that occurs when different Ecotypes or races of the same species geographically coexist The most widely accepted example of sympatric speciation is that of the cichlids of Lake Nabugabo in East Africa, which is thought to be due to sexual selection. Sympatric speciation refers to the formation of two or more descendant species from a single ancestral species all occupying the same geographic location.

Until recently, there has a been a dearth of hard evidence that supports this form of speciation, with a general feeling that interbreeding would soon eliminate any genetic differences that might appear. But there has been at least one recent study that suggests that sympatric speciation has occurred in Tennessee cave salamanders. ^[4]

The three-spined sticklebacks, freshwater fishes, that have been studied by Dolph Schluter (who received his Ph. D. for his work on Darwin's finches with Peter Grant) and his current colleagues in British Columbia, provide an intriguing example that is best explained by sympatric speciation. They have found:

• Two different species of three-spined sticklebacks in each of five different lakes.
  • a large benthic species with a large mouth that feeds on large prey in the littoral zone
  • a smaller limnetic species — with a smaller mouth — that feeds on the small plankton in open water.
• DNA analysis indicates that each lake was colonized independently, presumably by a marine ancestor, after the last ice age.
• DNA analysis also shows that the two species in each lake are more closely related to each other than they are to any of the species in the other lakes.
• Nevertheless, the two species in each lake are reproductively isolated; neither mates with the other.
• However, aquarium tests showed that
  • the benthic species from one lake will spawn with the benthic species from the other lakes and
  • likewise the limnetic species from the different lakes will spawn with each other.
  • These benthic and limnetic species even display their mating preferences when presented with sticklebacks from Japanese lakes; that is, a Canadian benthic prefers a Japanese benthic over its close limnetic cousin from its own lake.
• Their conclusion: in each lake, what began as a single population faced such competition for limited resources that
  • disruptive selection — competition favoring fishes at either extreme of body size and mouth size over those nearer the mean — coupled with
  • assortative mating — each size preferred mates like it - favored a divergence into two subpopulations exploiting different food in different parts of the lake.
  • The fact that this pattern of speciation occurred the same way on three separate occasions suggests strongly that ecological factors in a sympatric population can cause speciation.

Sympatric speciation driven by ecological factors may also account for the extraordinary diversity of crustaceans living in the depths of Siberia's Lake Baikal.

Speciation via polyploidization

Speciation via polyploidy: A diploid cell undergoes failed meiosis, producing diploid gametes, which self-fertilize to produce a tetraploid zygote. Polyploidy occurs in cells and Organisms when there are more than two homologous sets of Chromosomes. "Haplo" redirects here For the fictional character see The Death Gate Cycle. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked"

Polyploidy is a mechanism often attributed to causing some speciation events in sympatry. Polyploidy occurs in cells and Organisms when there are more than two homologous sets of Chromosomes. Sympatric speciation is the genetic divergence of various populations (from a single parent species inhabiting the same geographic region such that those populations become different 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 (see also hybrid speciation). A chromosome is an organized structure of DNA and Protein that is found in cells. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Hybrid speciation is the process wherein Hybridization between two different closely related Species leads to a distinct Phenotype.

Polyploidy is observed in many species of both plants and animals. In fact, it has been proposed that all of the existing plants and most of the animals are polyploids or have undergone an event of polyploidization in their evolutionary history.

Speciation via hybrid formation

Hybridization between two different species sometimes leads to a distinct phenotype. A phenotype is any observable characteristic of an Organism, such as its morphology, Development, biochemical or physiological properties This phenotype can also be fitter than the parental lineage and as such natural selection may then favor these individuals. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of Eventually, if reproductive isolation is achieved, it may lead to a separate species. An important concept in evolutionary biology reproductive isolation is a category of mechanisms that prevent two or more Populations from exchanging genes However, reproductive isolation between hybrids and their parents is particularly difficult to achieve and thus hybrid speciation is considered an extremely rare event.

Reinforcement

Reinforcement is the process by which natural selection increases reproductive isolation. An important concept in evolutionary biology reproductive isolation is a category of mechanisms that prevent two or more Populations from exchanging genes ^[5] It 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. In Biology, hybrid has two meanings The first meaning is the result of interbreeding between two animals or plants of different taxa. 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. The horse ( Equus caballus) is a hoofed ( Ungulate) Mammal, one of eight living species of the family Equidae. The donkey or ass, Equus asinus, is a member of the Equidae or horse family and an odd-toed ungulate. ) The reasoning behind this is that if the parents of the hybrid offspring each have naturally selected traits for their own certain environments, the hybrid offspring will bear traits from both, therefore would not fit either ecological niche as well as the parents did. The low fitness of the hybrids would cause selection to favor assortative mating, which would control hybridization. Assortative mating (also called assortative pairing) takes place when sexually reproducing Organisms tend to Mate with individuals that are like 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.

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. Hybrid zones are regions where diverged populations meet and interbreed. Hybrid offspring are very common in these regions, which are usually created by diverged species coming into secondary contact. Without reinforcement the two species would have uncontrollable inbreeding. 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. Animal husbandry, also called Animal science, stockbreeding or simple husbandry, is the agricultural practice of breeding For example, domestic sheep were created by hybridisation, and no longer produce viable offspring with Ovis orientalis, one species from which they are descended. The mouflon ( Ovis orientalis orientalis group is a subspecies group of the wild sheep Ovis orientalis. ^[6] Domestic cattle, on the other hand, can be considered the same species as several varieties of wild ox, gaur, yak, etc. Cattle, colloquially referred to as cows, are domesticated Ungulates a member of the Subfamily Bovinae of the family Oxen (singular ox) are Cattle trained as draft animals. Often they are adult castrated males The gaur (ˈɡaʊɚ ( Bos gaurus, previously Bibos gauris) is a large dark-coated bovine animal of South Asia and Southeast Asia. The yak ( Bos grunniens) is a long-haired Bovine found throughout the Himalayan region of south Central Asia, the Qinghai - , as they readily produce fertile offspring with them. ^[7]

The best-documented creations of new species in the laboratory were performed in the late 1980s. William Rice and G. W. Salt bred fruit flies, Drosophila melanogaster, using a maze with three different choices of habitat such as light/dark and wet/dry. Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order 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 were isolated reproductively because of their strong habitat preferences: they mated only within the areas they preferred, and so did not mate with flies that preferred the other areas. ^[8]

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. Allopatric speciation, also known as geographic Speciation, is the phenomenon whereby biological populations are physically isolated by an extrinsic barrier An important concept in evolutionary biology reproductive isolation is a category of mechanisms that prevent two or more Populations from exchanging genes ^[9] Dodd's experiment has been easy for many others to replicate, including with other kinds of fruit flies and foods. ^[10]

The Drosophila experiment conducted by Diane Dodd in 1989.

The history of such attempts is described in Rice and Hostert (1993). ^[11]

Genetics

Hybrid speciation

Main article: Hybrid speciation

Hybridization between two different species sometimes leads to a distinct phenotype. Hybrid speciation is the process wherein Hybridization between two different closely related Species leads to a distinct Phenotype. A phenotype is any observable characteristic of an Organism, such as its morphology, Development, biochemical or physiological properties This phenotype can also be fitter than the parental lineage and as such natural selection may then favor these individuals. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of Eventually, if reproductive isolation is achieved, it may lead to a separate species. An important concept in evolutionary biology reproductive isolation is a category of mechanisms that prevent two or more Populations from exchanging genes However, reproductive isolation between hybrids and their parents is particularly difficult to achieve and thus hybrid speciation is considered an extremely rare event. The Mariana Mallard arose from hybrid speciation. The Mariana Mallard ( Anas oustaleti)or Oustalet's Gray Duck is an Extinct Species of Duck of the Genus Anas

Hybridization without change in chromosome number is called homoploid hybrid speciation. A chromosome is an organized structure of DNA and Protein that is found in cells. It is considered very rare but has been shown in Heliconius butterflies ^[12] and sunflowers. Heliconius comprise a colorful and widespread nymphalid Butterfly Genus distributed throughout the tropical and subtropical regions of the New World A butterfly is an Insect of the order Lepidoptera. Like all Lepidoptera butterflies are notable for their unusual life cycle with a The sunflower ( Helianthus annuus) is an Annual plant in the family Asteraceae and native to the Americas, with a large flowering Polyploid speciation, which involves changes in chromosome number, is a more common phenomena, especially in plant species. Polyploidy occurs in cells and Organisms when there are more than two homologous sets of Chromosomes.

Gene transposition as a cause

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. Theodosius Grygorovych Dobzhansky, also known He mapped out how it might be possible for sections of chromosomes to relocate themselves in a genome. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby Those mobile sections can cause sterility in inter-species hybrids, which can act as a speciation pressure. In Biology, hybrid has two meanings The first meaning is the result of interbreeding between two animals or plants of different taxa. 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. ^[13]

However, recent research shows that jumping of a gene from one chromosome to another can contribute to the birth of new species. ^[14] This validates the reproductive isolation mechanism, a key component of speciation. ^[15]

Interspersed repeats

Main article: Interspersed repeat

Interspersed repetitive DNA sequences function as isolating mechanisms. 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 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. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Homologous chromosomes are Chromosomes in a Biological cell that pair ( synapse) during Meiosis, or alternatively non-identical chromosomes that The non-homologies create barriers to gene conversion. Gene conversion is an event in DNA Genetic recombination, which occurs at high frequencies during meiotic division but which also occurs in somatic cells This barrier allows nascent novel genes to evolve without being overwritten by the progenitors of these genes. An ancestor is a Parent or ( recursively) the parent of an ancestor (i This uncoupling allows the evolution of new genes, both within gene families and also allelic forms of a gene. A gene family is a set of Genes with a known homology. They are generally biochemically similar An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms The importance is that this allows the splitting of a gene pool without requiring physical isolation of the organisms harboring those gene sequences. In Population genetics, a gene pool is the complete set of unique Alleles in a Species or Population.

Human speciation

Humans have genetic similarities with chimpanzees and gorillas, suggesting common ancestors. Chimpanzee (often shortened to chimp) is the common name for the two extant Species of Apes in the Genus Pan. Gorillas, the largest of the living Primates are ground-dwelling Herbivores that inhabit the Forests of Africa. Analysis of genetic drift and recombination using a Markov model suggests humans and chimpanzees speciated apart 4. In Mathematics, a Markov chain, named after Andrey Markov, is a Stochastic process with the Markov property. 1 million years ago. ^[16]

See also

• Species problem
• Heteropatry
• Chronospecies
• Frozen plasticity
• Koinophilia

References

Further reading

• Coyne, J. A. & Orr, H. A. (2004). Speciation. Sunderlands, Massachusetts: Sinauer Associates, Inc. ISBN 0-87893-089-2.  
• Grant, V. (1981). Plant Speciation, 2nd Edit. , New York: Columbia University Press. ISBN 0-231-05113-1.  
• Mayr, E. (1963). Ernst Walter Mayr ( July 5, 1904, Kempten, Germany &ndash February 3, 2005, Bedford Massachusetts U Animal Species and Evolution. Harvard University Press. ISBN 0-674-03750-2
• White, M. J. D. (1978). Modes of Speciation. San Francisco, California: W. H. Freeman and Company. ISBN 0-716-70284-3.  
• Dedicated issue of Philosophical Transactions B on Speciation in microorganisms is freely available.

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