Презентация на тему: SPECIATION

SPECIATION
SUB TOPICS
FORMATION OF SPECIES
FORMATION OF SPECIES
TYPE OF SPECIATION
SPECIATION
ALLOPATRIC SPECIATION
SYMPATRIC SPECIATION
PERIPATRIC SPECIATION
PARAPATRIC SPECIATION
RESULT OF MICROEVOLUTION
SPECIATION IS THE SOURCE OF DIVERSITY IN WILDLIFE
EXAMPLE OF SYMPATRIC SPECIATION
EXAMPLE OF ALLOPATRIC SPECIATION
SPECIATION
EXAMPLE OF PERIPATRIC SPECIATION
EXAMPLE OF PARAPATRIC SPECIATION
SPECIATION
MAIN WAY AND MEAN OF SPECIATION
SPECIATION
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Первый слайд презентации: SPECIATION

BY :MOHAN KUMAR AMARNATH GROUP NO: 191 B TEACHER: SVETLANA SMIRNOVA

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Слайд 2: SUB TOPICS

FORMATION OF SPECIES RESULT OF MICROEVOLUTION SPECIATION IS THE SOURCE OF DIVERSITY IN WILDLIFE EXAMPLE OF SPECIATION MAIN WAY AND MEANS OF SPECIATION

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Слайд 3: FORMATION OF SPECIES

Speciation  is the  evolutionary  process by which populations evolve to become distinct  species. The biologist  Orator F. Cook  coined the term in 1906 for  cladogenesis, the splitting of lineages, as opposed to  anagenesis, phyletic evolution within lineages. Charles Darwin  was the first to describe the role of  natural selection  in speciation in his 1859 book  On the Origin of Species. He also identified  sexual selection  as a likely mechanism, but found it problematic. There are four geographic modes of speciation in nature, based on the extent to which speciating   populations  are isolated from one another:  allopatric,  peripatric,  parapatric, and  sympatric. Speciation may also be induced artificially, through  animal husbandry, agriculture, or  laboratory experiments. Whether  genetic drift  is a minor or major contributor to speciation is the subject matter of much ongoing discussion.

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Слайд 4: FORMATION OF SPECIES

Rapid sympatric speciation can take place through  polyploidy, such as by doubling of chromosome number; the result is progeny which are immediately  reproductively isolated  from the parent population. New species can also be created through  hybridization  followed, if the hybrid is favoured by natural selection, by reproductive isolation.

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Слайд 5: TYPE OF SPECIATION

ALLOPATRIC SPECIATION SYMPATRIC SPECIATION PERIPATRIC SPECIATION PARAPATRIC SPECIATION

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Слайд 6

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Слайд 7: ALLOPATRIC SPECIATION

During allopatric (from the ancient Greek  allos, "other" +  patrā, "fatherland") speciation, a population splits into two geographically isolated populations (for example, by  habitat fragmentation  due to geographical change such as  mountain formation ). The isolated populations then undergo genotypic or  phenotypic  divergence as: (a) they become subjected to dissimilar  selective  pressures; (b) they independently undergo genetic drift; (c) different  mutations  arise in the two populations. When the populations come back into contact, they have evolved such that they are reproductively isolated and are no longer capable of exchanging  genes.  Island genetics  is the term associated with the tendency of small, isolated genetic pools to produce unusual traits. Examples include  insular dwarfism  and the radical changes among certain famous island chains, for example on  Komodo. The  Galápagos Islands  are particularly famous for their influence on Charles Darwin. During his five weeks there he heard that  Galápagos tortoises  could be identified by island, and noticed that  finches  differed from one island to another, but it was only nine months later that he reflected that such facts could show that species were changeable. When he returned to  England, his speculation on evolution deepened after experts informed him that these were separate species, not just varieties, and famously that other differing Galápagos birds were all species of finches. Though the finches were less important for Darwin, more recent research has shown the birds now known as  Darwin's finches  to be a classic case of adaptive evolutionary radiation.

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Слайд 8: SYMPATRIC SPECIATION

Sympatric speciation  is the evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region. In  evolutionary biology  and  biogeography, sympatric and  sympatry  are terms referring to organisms whose  ranges  overlap so that they occur together at least in some places. If these organisms are closely related (e.g.  sister species ), such a distribution may be the result of sympatric  speciation.  Etymologically, sympatry is derived from the Greek roots  συν  ("together") and πα τρίς  ("homeland"). [1]  The term was coined by  Edward Bagnall Poulton  in 1904, who explains the derivation. Sympatric speciation is one of three traditional geographic modes of speciation.  Allopatric speciation  is the evolution of species caused by the geographic isolation of two or more populations of a species. In this case, divergence is facilitated by the absence of gene flow.  Parapatric speciation  is the evolution of geographically adjacent populations into distinct species. In this case, divergence occurs despite limited interbreeding where the two diverging groups come into contact. In sympatric speciation, there is no geographic constraint to interbreeding. These categories are special cases of a continuum from zero (sympatric) to complete (allopatric) spatial segregation of diverging groups.

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Слайд 9: PERIPATRIC SPECIATION

In peripatric speciation, a subform of allopatric speciation, new species are formed in isolated, smaller peripheral populations that 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. Case studies include Mayr's investigation of bird fauna; the Australian bird  Petroica multicolor ; and reproductive isolation in populations of  Drosophila  subject to population bottlenecking.

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Слайд 10: PARAPATRIC SPECIATION

n parapatric speciation, there is only partial separation of the zones of two diverging populations afforded by geography; individuals of each species may come in contact or cross habitats from time to time, but reduced fitness of the  heterozygote  leads to selection for behaviour or mechanisms that prevent their  interbreeding. Parapatric speciation is modelled on continuous variation within a "single," connected habitat acting as a source of natural selection rather than the effects of isolation of habitats produced in peripatric and allopatric speciation. Parapatric speciation may be associated with differential landscape-dependent  selection. Even if there is a  gene flow  between two populations, strong differential selection may impede assimilation and different species may eventually develop. Habitat differences may be more important in the development of reproductive isolation than the isolation time. Caucasian rock lizards  Darevskia   rudis,  D. valentini  and  D. portschinskii  all  hybridize  with each other in their  hybrid zone ; however, hybridization is stronger between  D. portschinskii  and  D. rudis, which separated earlier but live in similar habitats than between  D. valentini  and two other species, which separated later but live in climatically different habitats.

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Слайд 11: RESULT OF MICROEVOLUTION

Microevolution  is the change in  allele frequencies  that occurs over time within a population. This change is due to four different processes:  mutation, selection ( natural  and  artificial ),  gene flow  and  genetic drift. This change happens over a relatively short (in evolutionary terms) amount of time compared to the changes termed  macroevolution. Population genetics  is the branch of biology that provides the mathematical structure for the study of the process of microevolution.  Ecological genetics  concerns itself with observing microevolution in the wild. Typically, observable instances of  evolution  are examples of microevolution; for example,  bacterial  strains that have  antibiotic resistance. Microevolution may lead to  speciation, which provides the raw material for  macroevolution.

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Слайд 12: SPECIATION IS THE SOURCE OF DIVERSITY IN WILDLIFE

Speciation  is the ultimate source of new species, in the same way that mutation is the ultimate source of genetic variation within species (and extinction is analogous to loss of alleles). Inequities in the rates of  speciation  are thus likely to contribute to large scale  biodiversity  patterns

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Слайд 13: EXAMPLE OF SYMPATRIC SPECIATION

There are two sources of food for them to choose from: red apples and green apples. At first, all of the flies feed on red apples, but at some point, some of the flies begin to prefer green apples. Sympatric speciation occurs if interactions are so limited between these groups that mating no longer occurs between them. Each new population of flies will have genetic variation in its gene pool, which is the collective genetic information for the group. As they continue to mate with other members of their new group, these variations will become more prevalent in the population. Over a long enough period of time, an entirely new species might develop

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Слайд 14: EXAMPLE OF ALLOPATRIC SPECIATION

A major example of allopatric speciation occurred in the Galapagos finches that Charles Darwin studied. There are about 15 different species of finches on the Galapagos islands, and they each look different and have specialized beaks for eating different types of foods, such as insects, seeds, and flowers. All of these finches came from a common ancestor species that must have emigrated to the different islands. Once populations were established on the islands, they became isolated from each other and different mutations arose. The mutations that caused the birds to be most successful in their respective environments became more and more prevalent, and many different species formed over time. When many new species emerge from one common ancestor in a relatively quickly geological timeframe, this is called  adaptive radiation.

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Слайд 16: EXAMPLE OF PERIPATRIC SPECIATION

The  figwart  plant species  Scrophularia lowei  is thought to have arisen through a peripatric speciation event, with the more widespread mainland species,  Scrophularia arguta  dispersing to the  Macaronesian  islands. Other members of the same genus have also arisen by single colonization events between the islands The occurrence of peripatry on continents is more difficult to detect due to the possibility of vicariant explanations being equally likely. However, studies concerning the Californian plant species  Clarkia   biloba  and  C. lingulata   strongly suggest a peripatric origin. In addition, a great deal of research has been conducted on several species of land snails involving  chirality  that suggests peripatry (with some authors noting other possible interpretations).

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Слайд 17: EXAMPLE OF PARAPATRIC SPECIATION

The best-known  example  of incipient  parapatric speciation  occurs in populations of the grass Agrostis tenuis which span mine tailings and normal soils. Individuals that are tolerant to heavy metals, a heritable trait, survive well on contaminated soil, but poorly on non-contaminated soil

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Слайд 19: MAIN WAY AND MEAN OF SPECIATION

Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through mechanisms that occur within a shared habitat (sympatric speciation). Both pathways force reproductive isolation between populations. Sympatric speciation can occur through errors in meiosis that form gametes with extra chromosomes, called polyploidy. Autopolyploidy occurs within a single species, whereas allopolyploidy occurs because of a mating between closely related species. Once the populations are isolated, evolutionary divergence can take place leading to the evolution of reproductive isolating traits that prevent interbreeding should the two populations come together again. The reduced viability of hybrid offspring after a period of isolation is expected to select for stronger inherent isolating mechanisms.

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