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Ein '''genetisches Isolat''' ist eine [[Population (Biologie)|Population]] von [[Lebewesen|Organismen]], die eine geringe oder keine [[Genetik|genetische]] Vermischung mit anderen Organismen derselben Art aufweist.
{{More citations needed|date=October 2014}}
In einigen Fällen kann es zur [[Artbildung]] (Speziation) kommen, aber das muss nicht unbedingt der Fall sein.
Der Begriff bezieht sich auf gewöhnlich auf Organismen mit [[geschlechtliche Fortpflanzung|geschlechtlicher Fortpflanzung]], wie sie gewöhnlich bei [[Eukaryoten]], insbesondere Tieren und Pflanzen, vorkommt. Allgemein ist Voraussetzung, dass die Individuen einer Population normalerweise im ständigen Austausch ([[Genfluss]]) ihrer genetischen Information stehen (etwa durch [[Rekombination (Genetik)|Rekombination]] und/oder [[Reassortment]]).
[[Isolation (Biologie)|Genetische oder reproduktive Isolation]] ist dann das Ausbleiben dieser Vermischung durch Unterbrechung des Genflusses.<ref name="Arcos-Burgos2002"/><ref name="Campbell2011"/><ref name="Mayr1970"/>


== Ursachen genetischer Isolation ==
== Introduction ==
{{Hauptartikel|Isolationsmechanismen}}
Geographic isolation or other factors that prevent reproduction have resulted in a population of organisms with a change in genetic diversity and ultimately leads to the genetic isolation of species. Genetic isolates form new species through an evolutionary process known as speciation. Today, all the species diversity present on earth is the product of genetic isolate and evolution. The current distribution of genetic differences and isolation within and among populations is also influenced by genetic processes, which can give significant input into evolution's basic principles. The resulting genetic diversity within a species' distribution range is frequently unequally distributed, and large disparities can occur at the series of ranges when population dispersion and isolation are critical for species survival.<ref>{{Cite journal|last1=Tóth|first1=Endre Gy|last2=Tremblay|first2=Francine|last3=Housset|first3=Johann M.|last4=Bergeron|first4=Yves|last5=Carcaillet|first5=Christopher|date=2019-10-17|title=Geographic isolation and climatic variability contribute to genetic differentiation in fragmented populations of the long-lived subalpine conifer Pinus cembra L. in the western Alps|url=http://dx.doi.org/10.1186/s12862-019-1510-4|journal=BMC Evolutionary Biology|volume=19|issue=1|page=190|doi=10.1186/s12862-019-1510-4|pmid=31623551|pmc=6798344|issn=1471-2148}}</ref> The interrelationship of genetic drift, gene flow, and natural selection determines the level and dispersion of genetic differences between populations and among species assemblages.<ref>{{Cite journal|last1=ECKERT|first1=C. G.|last2=SAMIS|first2=K. E.|last3=LOUGHEED|first3=S. C.|date=March 2008|title=Genetic variation across species' geographical ranges: the central–marginal hypothesis and beyond|url=http://dx.doi.org/10.1111/j.1365-294x.2007.03659.x|journal=Molecular Ecology|volume=17|issue=5|pages=1170–1188|doi=10.1111/j.1365-294x.2007.03659.x|pmid=18302683|s2cid=13746514|issn=0962-1083}}</ref> Geographic and natural elements may likewise add to these cycles and further impact species' advanced examples of hereditary variety such as genetic differences that cause genetic isolation.<ref>{{Cite journal|last1=Marchelli|first1=P|last2=Gallo|first2=L A|date=September 2001|title=Genetic diversity and differentiation in a southern beech subjected to introgressive hybridization|url=http://dx.doi.org/10.1046/j.1365-2540.2001.00882.x|journal=Heredity|volume=87|issue=3|pages=284–293|doi=10.1046/j.1365-2540.2001.00882.x|pmid=11737275|s2cid=22211025|issn=0018-067X}}</ref> Genetic variations are often unequally distributed over a species' geographic distribution, with differences between populations at the geographic center and the range's extremities.<ref>{{Cite journal|last1=Hampe|first1=Arndt|last2=Petit|first2=Rémy J.|date=2005-03-07|title=Conserving biodiversity under climate change: the rear edge matters|url=http://dx.doi.org/10.1111/j.1461-0248.2005.00739.x|journal=Ecology Letters|volume=8|issue=5|pages=461–467|doi=10.1111/j.1461-0248.2005.00739.x|pmid=21352449|issn=1461-023X}}</ref> In general, significant gene flow occurs in core populations, resulting in genetic uniformity, whereas low gene flow, severe genetic drift, and diverse selection conditions occur in range periphery populations, resulting in enhanced genetic isolation and heterogeneity among populations.<ref>{{Cite journal|last1=Brunet|first1=Johanne|last2=Larson-Rabin|first2=Zachary|last3=Stewart|first3=Christy M.|date=June 2012|title=The Distribution of Genetic Diversity Within and Among Populations of the Rocky Mountain Columbine: The Impact of Gene Flow, Pollinators, and Mating System|url=http://dx.doi.org/10.1086/665263|journal=International Journal of Plant Sciences|volume=173|issue=5|pages=484–494|doi=10.1086/665263|s2cid=84162712|issn=1058-5893}}</ref> Genetic differentiation resulted from genetic isolate occurs as significant alterations in genetic variations, such as fluctuations in allelic frequencies, that are accumulated in the populations over time with geographic regional boundaries. Significant genetic diversity can be detected towards the limits of a species' range, where population fragmentation and isolation are more likely to affect genetic processes. Fragmentation is the division of a large population into smaller, geographically separated habitats, resulting in genetic differences within and across groups is also the product of genetic isolate.<ref>{{Cite journal|last1=Provan|first1=Jim|last2=Maggs|first2=Christine A.|date=2011-05-18|title=Unique genetic variation at a species' rear edge is under threat from global climate change|url=http://dx.doi.org/10.1098/rspb.2011.0536|journal=Proceedings of the Royal Society B: Biological Sciences|volume=279|issue=1726|pages=39–47|doi=10.1098/rspb.2011.0536|pmid=21593035|pmc=3223643|issn=0962-8452}}</ref> Regional splitting is produced by a variety of factors, including environmental processes that regularly change a species' indigenous distribution.<ref>{{Cite journal|last1=Hampe|first1=Arndt|last2=Petit|first2=Rémy J.|date=2005-03-07|title=Conserving biodiversity under climate change: the rear edge matters|url=http://dx.doi.org/10.1111/j.1461-0248.2005.00739.x|journal=Ecology Letters|volume=8|issue=5|pages=461–467|doi=10.1111/j.1461-0248.2005.00739.x|pmid=21352449|issn=1461-023X}}</ref> Additionally, human-caused environmental changes, such as deforestation, land degradation can result in fast changes in a species' distribution, resulting in population decrease, segmentation, and regional isolation . Consequently, communities became geographically and genetically isolated.<ref>{{Cite journal|last1=Cheptou|first1=Pierre-Olivier|last2=Hargreaves|first2=Anna L.|last3=Bonte|first3=Dries|last4=Jacquemyn|first4=Hans|date=2017-01-19|title=Adaptation to fragmentation: evolutionary dynamics driven by human influences|url=http://dx.doi.org/10.1098/rstb.2016.0037|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=372|issue=1712|pages=20160037|doi=10.1098/rstb.2016.0037|pmid=27920382|pmc=5182433|issn=0962-8436}}</ref>
Genetische Isolate können auf verschiedene Weise zur Entstehung neuer Arten führen:<ref name="Arcos-Burgos2002"/><ref name="Campbell2011"/><ref name="Mayr1970"/>
* [[Allopatrische Speziation]]: Bei dieser werden zwei Populationen derselben Art durch eine äußere Barriere geografisch voneinander getrennt und entwickeln eine intrinsische (genetische) reproduktive Isolation.
* [[Isolationsmechanismen#Peripatrische Speziation|Peripatrische Speziation]]: Hier wird eine kleine Gruppe einer Population von der Hauptpopulation getrennt und erfährt eine genetische Drift infolge von [[Selektionsdruck]].
* [[Parapatrische Speziation]]: Die Kerngebiete der Zonen zweier unterschiedlicher Populationen sind hier getrennt, in ihren Randgebieten kommt es aber zu regionalen Überschneidungen. Die teilweise Trennung wird ebenfalls durch die Geographie garantiert, sodass Individuen jeder Population von Zeit zu Zeit miteinander in Kontakt kommen können. Die Auswahl nach bestimmten Verhaltensweisen oder Mechanismen (beispielsweise Im Balzverhalten oder der genauen Melodie des Vogelgesangs) kann die Fortpflanzung zwischen den beiden Gruppen verhindern.
* [[Sympatrische Speziation]]: Dies ist eine umstrittene Artbildungsmethode, bei der Arten sich zweiteilen, während sie denselben Ort bewohnen.
Die ersten beiden Szenarien führen zur [[Geografische Isolation|geografischen Isolation]], das letzte zur [[Isolation (Biologie)#Ökologische Isolation|ökologischen Isolation]], das dritte stellt eine Mischform dar.


Zu den menschlichen Einflüssen auf genetische Isolate gehört eine genetische Durchmischung von Haustieren begrenzende [[Rasse (Züchtung)#Kulturrassen|Rassezucht]] (Beispiele: [[Hundezucht]] und [[Hauskaninchen#Zucht|Kaninchenzucht]]); analog die [[Pflanzenzüchtung|Zucht neuer Sorten von Nutz- und Kulturpflanzen]] (Beispiele: [[Kartoffelsorten]], [[Rosensorten]] und [[Weizen#Sorten|Weizensorten]] – nicht [[Weizen|-arten]]).
== History ==
Isolation, in combination with diminishing habitat quality and a limited population density, is likely to result in a population's collapse and ultimate demise and extinction.<ref>{{Cite journal|last1=Sterling|first1=Ken A.|last2=Reed|first2=David H.|last3=Noonan|first3=Brice P.|last4=Warren|first4=Melvin L.|date=2012-03-28|title=Genetic effects of habitat fragmentation and population isolation on Etheostoma raneyi (Percidae)|url=http://dx.doi.org/10.1007/s10592-012-0335-0|journal=Conservation Genetics|volume=13|issue=3|pages=859–872|doi=10.1007/s10592-012-0335-0|s2cid=14016133|issn=1566-0621}}</ref> Random mutation rate, drift, high rates of inbreeding, restricted gene flow, and regional extinction have all been shown to increase with isolation. Varying climatic conditions, such as particular geographic climatic changes, can potentially cause pressures, which can drastically change a species' genetic composition yielding differences through starkly different selection processes.<ref>{{Cite journal|last1=Kreyling|first1=Juergen|last2=Buhk|first2=Constanze|last3=Backhaus|first3=Sabrina|last4=Hallinger|first4=Martin|last5=Huber|first5=Gerhard|last6=Huber|first6=Lukas|last7=Jentsch|first7=Anke|last8=Konnert|first8=Monika|last9=Thiel|first9=Daniel|last10=Wilmking|first10=Martin|last11=Beierkuhnlein|first11=Carl|date=2014-02-07|title=Local adaptations to frost in marginal and central populations of the dominant forest tree F agus sylvatica L . as affected by temperature and extreme drought in common garden experiments|url=http://dx.doi.org/10.1002/ece3.971|journal=Ecology and Evolution|volume=4|issue=5|pages=594–605|doi=10.1002/ece3.971|pmid=25035801|pmc=4098140|issn=2045-7758}}</ref> as well as lead to increased genetic isolation among populations on a landscape heterogeneity.<ref>{{Cite journal|last1=Bockelmann|first1=A.-C.|last2=Reusch|first2=T. B. H.|last3=Bijlsma|first3=R.|last4=Bakker|first4=J. P.|date=February 2003|title=Habitat differentiation vs. isolation-by-distance: the genetic population structure of Elymus athericus in European salt marshes|url=http://dx.doi.org/10.1046/j.1365-294x.2003.01706.x|journal=Molecular Ecology|volume=12|issue=2|pages=505–515|doi=10.1046/j.1365-294x.2003.01706.x|pmid=12535100|s2cid=23544230|issn=0962-1083}}</ref> Environmental heterogeneity has historically been identified as a vital source of genetic variations and distinctions due to isolation, and several studies have found correlations between neutral genetic differences and ecological heterogeneity, and genetic isolation. The genetic isolation and different associations in regional heterogeneity could be cited as evidence of diversifying selection working across entire genomes, encompassing manifestly neutral genes, and can be used to predict long-term effects of environmental factors on genetic diversity and genetic isolation.<ref>{{Cite journal|last1=Jiang|first1=Xiao-Long|last2=An|first2=Miao|last3=Zheng|first3=Si-Si|last4=Deng|first4=Min|last5=Su|first5=Zhi-Hao|date=2017-12-27|title=Geographical isolation and environmental heterogeneity contribute to the spatial genetic patterns of Quercus kerrii (Fagaceae)|url=http://dx.doi.org/10.1038/s41437-017-0012-7|journal=Heredity|volume=120|issue=3|pages=219–233|doi=10.1038/s41437-017-0012-7|pmid=29279604|pmc=5836588|issn=0018-067X}}</ref>


== Isolate und Subspezies aufgrund allopatrischer Speziation bei Giraffen ==
== Definition ==
Wenn sich eine Art in zwei verschiedene Gruppen aufspaltet, die voneinander isoliert sind, wird dies als allopatrische Speziation (Artbildung) bezeichnet.<ref name="NGS"/>
'''Genetic [https://www.biologyonline.com/dictionary/isolation isolation]''' is population of [[organism]]s that has little genetic mixing with other organisms within the same species. This may result in [[speciation]], but this is not necessarily the case. Genetic isolates may form new species in several ways:
Die [[Giraffe]] (''Giraffa camelopardalis''),<ref name="AD-Gc"/> ist ein Beispiel für die allopatrische (Unter-)Artbildung, wie sie durch die genetische Isolierung einer Population entsteht.
Mehrere Giraffen[[klade]]n weisen Unterschiede in ihrer [[mtDNA|mitochondrialen DNA]] (mtDNA) auf, die zwischen verschiedenen Regionen Afrikas variieren. Diese Unterschiede gehen auf die Mitte des [[Pleistozän]]s zurück und fallen mit der genetischen Isolation aufgrund klimatischer und geografischer Trennungen innerhalb der Populationen zusammen, was die Entwicklung und Unterspeziation der verschiedenen Unterarten der Giraffe und die Unterschiede in ihrer Farbmuster ermöglichte.<ref name="Brown2007"/>


== Genetische Isolate beim Jetztmenschen ==
* [[Allopatric speciation]], in which two populations of the same species are geographically isolated from one another by an extrinsic barrier, and evolve intrinsic (genetic) reproductive isolation
Genetische Isolate beim Jetztmenschen (''[[Homo sapiens]]'') selbst findet man bei Gemeinschaften, die abgeschieden von anderen leben, wie auf [[Tristan da Cunha]] oder den [[Pitcairn-Inseln]]. Weitaus größere und weniger abgelegene menschliche genetische Isolate sind [[Völker]] wie in Europa die [[Sarden]] oder auch die [[Finnen]], die [[Ureinwohner]] [[Sardinien]]s bzw. [[Finnland]]s.<ref name="Arcos-Burgos2002"/> Beispiele in Asien sind
* [[Peripatric speciation]], in which a small group of a population is separated from the main population, and experiences [[genetic drift]]
* die Ureinwohner der [[Andamanen]] (insbesondere die [[Sentinelesen|Sentineli]]),
* [[Parapatric speciation]], in which zones of two diverging populations are separate, but do overlap somewhat; partial separation is afforded by geography, so individuals of each species may come in contact from time to time, but selection for specific behaviors or mechanisms may prevent breeding between the two groups.
* die [[Aeta]] auf [[Luzon]] ([[Philippinen]]),
* [[Sympatric speciation]], a contentious method of speciation in which species diverge while inhabiting the same place.
* in [[Japan]] im Norden die [[Ainu]] auf [[Hokkaido]], im Süden die [[Ryūkyū-Völker]] u.&nbsp;a. auf [[Okinawa]]),
* auf der chinesischen Insel [[Hainan]] z.&nbsp;B die [[Hlai]] vom [[Li (Volk)|Li-Volk]],
* sowie die [[Indigene Völker Taiwans|indigenen Völker Taiwans]].


== Isolation und Bedrohung durch Aussterben ==
Human influences on genetic isolates include restricted [[Dog breeding|breeding of dogs]], or a community living secluded away from others (such as [[Tristan da Cunha]] or [[Pitcairn Islands]]). Far larger and less secluded human genetic isolates are peoples like [[Sardinians]] or also the [[Finns]], natives of [[Finland]].
Isolation in Kombination mit abnehmender Lebensraumqualität und Populationsdichte kann mit großer Wahrscheinlichkeit zum Zusammenbruch einer Population und schließlich zu deren Aussterben führen.<ref name="Sterling2012"/>
Es ist erwiesen, dass die zufällige [[Mutation]]srate, Drift, hohe [[Inzucht]]qouten, eingeschränkter Genfluss und regionales Aussterben mit der Isolation zunehmen.
Unterschiedliche klimatische Bedingungen, wie geografische [[Klimawandel|Klimaveränderungen]], können zu Belastungen führen, die die genetische Zusammensetzung einer Art drastisch verändern und durch regional stark unterschiedliche Selektionsprozesse zu Unterschieden im [[Genpool]] führen,<ref name="Kreyling2014"/>
sowie zu einer verstärkten genetischen Isolation zwischen Populationen in einer heterogenen Landschaft.<ref name="Bockelmann2003"/>
Umweltheterogenität wurde in der Vergangenheit als wichtige Quelle für genetische Variationen und Unterschiede aufgrund von Isolation identifiziert<!--, und mehrere Studien haben Korrelationen zwischen neutralen genetischen Unterschieden und ökologischer Heterogenität sowie genetischer Isolation festgestellt -- Orig: and several studies have found correlations between neutral genetic differences and ecological heterogeneity, and genetic isolation -- neutral??? -->.
Genetische Isolation und die Auswirkungen regional unterschiedlicher Lebensumstände können als Beleg für eine diversifizierende Selektion angeführt werden, die über das gesamte Genom hinweg wirkt und auch offensichtlich neutrale Gene umfasst. Dies kann zur Vorhersage langfristiger Auswirkungen von Umweltfaktoren auf die genetische Vielfalt und die genetische Isolation herangezogen werden.<ref name="Jiang2017"/>


== Stark fragmentierte Populationen ==
== Genetic Isolation and the ''Giraffa camelopardalis'' ==
Der Zusammenhang zwischen der Statistik genetischer Unterschiede und der Populationsgröße wurde bisher wissenschaftlich kaum beachtet, obwohl kleine Populationen eine geringere genetische Variation an [[Marker (Genetik)|Markerloci]] aufweisen. Es ließ sich zeigen, dass in kleineren fragmentierten Meta-Populationen sowohl die neutrale als auch die quantifizierbare genetische Variation reduziert ist und sowohl die Drift als auch die selektionsbedingte Veränderungen verstärkt werden.<ref name="Willi2007"/>
Genetic isolation can happen in a variety of different ways. There are many ongoing, current research projects evaluating how various species have diverged through the process of genetic isolation, the [[giraffe]], ''[https://animaldiversity.org/accounts/Giraffa_camelopardalis/ Giraffa camelopardalis]'', being one example. Giraffes are recognized to have nine separate subspecies, each varying in their coloration and patterns.<ref name=Website>{{cite web|title=Giraffe Subspecies|url=http://www.giraffeconservation.org/giraffe_facts.php?pgid=6|website=Giraffe Conservation Foundation|access-date=23 October 2014|archive-date=30 June 2015|archive-url=https://web.archive.org/web/20150630164208/http://www.giraffeconservation.org/giraffe_facts.php?pgid=6|url-status=dead}}</ref> After much research, it accepts that genetic [https://www.biologyonline.com/dictionary/isolation isolation] is at fault for allowing the ''G. Camelopardalis'' species to diverge. There are various ideas behind how genetic isolation has occurred within the giraffe species. Extant giraffe populations have been studying to make small-scale migratory movements based on the African climate's wet and dry seasons.<ref name="Pellew 1984">{{cite journal|last1=Pellew|first1=R|title=The feeding ecology of a selective browser, the giraffe (Giraffa camelopardalis tippelskirchi|journal=Journal of Zoology|date=1984|pages=57–81|doi=10.1111/j.1469-7998.1984.tb04288.x|volume=202}}</ref> The feeding ecology of giraffes is highly researching. It has shown that giraffes will follow the growth patterns of the Acacia tree based upon seasonal change, changing giraffe locations from mountain ranges to desert ranges.<ref name="Fennessy 2009">{{cite journal|last1=Fennessy|first1=J|title=Home range and seasonal movements of Giraffa camelopardalis angolensis in the northern Namib Desert|journal=African Journal of Ecology|date=2009|pages=318–327|doi=10.1111/j.1365-2028.2008.00963.x|volume=47|issue=3}}</ref> Though this is not evidence for current-day genetic isolation, it suggests evidence for past large-scale migrations that may have caused separation within the species, caused genetic isolation and led to the beginnings of the subspeciation of the giraffe population. Giraffes also tend to travel in loose social herds. However, these loose social herds have been researching to be base upon a non-random system. This non-random system follows a trend of kinship or the sharing of similar genes between individuals. These loose-social herds keep kin and familiar individuals within the same group, with only slight movements of individuals from the pack, only to return to the same group.<ref name="Bercovitch 2013">{{cite journal|last1=Bercovitch|first1=F.B.|title=Herd composition, kinship and fission–fusion social dynamics among wild giraffe|journal=African Journal of Ecology|date=2013|pages=206–216|doi=10.1111/aje.12024|volume=51|issue=2}}</ref> This is evidence for genetic isolation by interaction only between familiar individuals. This is the cause for interbreeding and the accumulation of specific alleles. These alleles could potentially code for pelage color and pattern within a population, causing differences between people and ultimately the subspeciation of the giraffe species. Geographic separation has also been studying to play a role in the genetic isolation of the giraffe. The [[mitochondrial DNA]] of the giraffe has been looking for mutations and loci substitutions between subspecies and suggests diversification around the Late Pleistocene, where geographic isolation was likely.<ref name="Hassanin 2007">{{cite journal|last1=Hassanin|first1=A|title=Mitochondrial DNA variability in Giraffa camelopardalis: consequences for taxonomy, phylogeography and conservation of giraffes in West and central Africa|journal=Comptes Rendus Biologies|date=2007|pages=265–274|doi=10.1016/j.crvi.2007.02.008|pmid=17434121|volume=330|issue=3}}</ref> The giraffe is an excellent example of how genetic isolation can happen in some ways and lead to species diversification.


== Sympatrische Spezies durch Klimaeinflüsse ==
== Allopatric Speciation ==
Die Anpassung an unterschiedliche klimatische Bedingungen kann eine wichtige Quelle für genetische Unterschiede und die Isolation von Populationen sein.<!-- [[Pleiotrop]]e sexuelle Selektion zwischen Individuen dieser genetisch unterschiedlichen Populationen kann durch biologische Merkmale ausgelöst werden, die in jedem Lebensraum ausgewählt wurden. Dieser Umstand könnte die sympatrische Speziation erleichtern. -- Original: Pleiotropic induced sexual selection between individuals of these genetically diverse populations can be induced by biological features selected in each habitat. This circumstance could make sympatric speciation easier.-->
The giraffe, ''[https://animaldiversity.org/accounts/Giraffa_camelopardalis/ Giraffa camelopardalis]'', can represent the allopatric speciation that occurs due to the genetic isolation of a population. Several clades of giraffes show differentiation within their mitochondrial DNA, varying between regions throughout Africa. These differences date back to the middle of the Pleistocene epoch and coincide with genetic isolation due to climatic and geographical separations within the population, allowing for the evolution and subspeciation of the separate subspecies of giraffe and differences in their pelage.<ref>{{cite journal | last1 = Brown | first1 = D. M. | last2 = Brenneman | first2 = R. A. | last3 = Koepfli | first3 = K. P. | last4 = Pollinger | first4 = J. P. | last5 = Milá | first5 = B. | last6 = Georgiadis | first6 = N. J. | last7 = Wayne | first7 = R. K. | year = 2007 | title = Extensive population genetic structure in the giraffe | journal = BMC Biology | volume = 5 | issue = 1| page = 57 | doi=10.1186/1741-7007-5-57 | pmid=18154651 | pmc=2254591}}</ref> In addition, When a species splits into two different groups that are isolated from one another, this is known as allopatric speciation (1).<ref>{{Cite web|last=Society|first=National Geographic|date=2011-01-21|title=speciation|url=http://www.nationalgeographic.org/encyclopedia/speciation/|access-date=2021-09-24|website=National Geographic Society|language=en}}</ref>
So liefern beispielsweise erfolgreiche [[Wirt (Biologie)|Wirts]]<nowiki/>wechsel bei Pflanzenschädlingen unter den Insekten einige der überzeugendsten Beweise für ökologische Diversifizierung bei sympatrischer Artbildung<ref name="Thomas2003"/>


== Genetische Isolate und die Auswirkungen der genetischen Vielfalt ==
== Genetic isolation and speciation ==
Arten mit enormen ökologischen Bandbreiten weisen im Allgemeinen eine große genetische Vielfalt auf.
A genetic species is a collection of biologically compatible crossbreeding natural populations that are genetically distinct from genetically related populations. The Genetic species concept, in contrast to the biological species concept, emphasizes genetic isolation rather than reproductive separation. The finding of genetically separate but not reproductively isolated species advances our knowledge of biodiversity, speciation, and related issues, as well as organism evolution. Consider the evolution of two allopatric populations. Over lengthy periods, each group undergoes numerous substitutions, resulting in genetic differentiation and isolation. Would it be possible to transplant a divergent gene from one group into the genome of another? On this connected genetic background, it's simple to see the gene being reasonably successful. That's also easy to see how it wouldn't work out because they are now genetically isolated from one another.<ref>{{Cite journal|last1=Baker|first1=Robert J.|last2=Bradley|first2=Robert D.|title=Speciation in Mammals and the Genetic Species Concept|date=August 2006|url=http://dx.doi.org/10.1644/06-mamm-f-038r2.1|journal=Journal of Mammalogy|volume=87|issue=4|pages=643–662|doi=10.1644/06-mamm-f-038r2.1|pmid=19890476|pmc=2771874|issn=0022-2372}}</ref>
Stärker spezialisierte Arten mit geringer ökologischer Bandbreite und Häufigkeit haben dagegen nur eine geringe genetische Vielfalt. Inzuchtdepressionen, d.&nbsp;h. Verringerung der genetischen Vielfalt (im [[Genpool]]) aufgrund von [[Inzucht]] stellen vielleicht die größte Bedrohung für Arten mit mäßigen Lebensraumansprüchen und großer genetischer Vielfalt dar.<ref name="Habel2012"/>


== Genetische Isolate auf Inseln ==
== Genetic isolation by environment or distance ==
Das Phänomen der genetischen Isolation unter den speziellen Bedingungen mehr oder weniger kleiner Inseln wurde von Haider ''et&nbsp;al.'' 2012 untersucht,<!-- Climatic differentiation, as a single factor is included as separate variability, provides to decreases in immigration and reproduction in as many species belongs to a wide range of herbs families and with variable amounts of evolutionary understanding. The genetic structure of species on an isolated island is influenced by a range of environmental variables, with some species being influenced by single contours and others being influenced by many species. Sister species and congenerics have various contributing elements to isolation within species.--><ref name="Haider2012"/> siehe auch [[Inselverzwergung]].
Strong gene flow across populations can help local adaptation by bringing new genetic variations for selection, but it can also impede adaptation by clogging up locally beneficial genes. The population size, genetic diversity, and the environment can all have an impact on the outcome. IBD (isolation by distance), wherein population growth rates and immigration numbers are inversely proportional to population distance, may correlate gene flow patterns with geographic distance. Gene flow may also follow patterns of isolation by habitat, with higher rates of gene flow among an increasingly common form. Moreover, gene flow may be greatest across areas that are dissimilar which is the typical genomic swamping situation.<ref>{{Cite journal|last1=Sexton|first1=Jason P.|last2=Hangartner|first2=Sandra B.|last3=Hoffmann|first3=Ary A.|title=Genetic Isolation by Environment or Distance: Which Pattern of Gene Flow is Most Common?|date=January 2014|url=https://onlinelibrary.wiley.com/doi/10.1111/evo.12258|journal=Evolution|language=en|volume=68|issue=1|pages=1–15|doi=10.1111/evo.12258|pmid=24111567|s2cid=10975665}}</ref> When the population’s size is limited and individuals are subjected to strong selection, gene flow can boost population numbers, even if the phenotypes that arise are generally miss-adapted. This can lead to increases in genetic differences that lead to isolation, which can allow new adaptations to take hold and even enlarge a habitat zone.<ref>{{Cite journal|last1=Holt|first1=Robert D.|last2=Gomulkiewicz|first2=Richard|date=March 1997|title=How Does Immigration Influence Local Adaptation? A Reexamination of a Familiar Paradigm|url=http://dx.doi.org/10.1086/286005|journal=The American Naturalist|volume=149|issue=3|pages=563–572|doi=10.1086/286005|s2cid=83733282|issn=0003-0147}}</ref>


== Literatur ==
=== Genetic isolation in fragmented populations ===
* {{Cite journal |last1=Baker|first1=Robert J. |last2=Bradley|first2=Robert D. |title=Speciation in Mammals and the Genetic Species Concept |date=2006-08 |url=https://academic.oup.com/jmammal/article/87/4/643/962134?login=false |journal=Journal of Mammalogy |volume=87 |issue=4 |pages=643–662 |doi=10.1644/06-mamm-f-038r2.1 |pmid=19890476 |pmc=2771874 |issn=0022-2372}}
The link between statistical genetic differences and population size has gotten little scientific attention, despite the fact that small populations have less genetic variation at marker loci. Researchers show that in smaller fragmented meta-population, both neutral and quantifiable genetic variation is reduced, and both drift and selection change is amplified.<ref>{{Cite journal|last1=WILLI|first1=Y.|last2=VAN BUSKIRK|first2=J.|last3=SCHMID|first3=B.|last4=FISCHER|first4=M.|date=March 2007|title=Genetic isolation of fragmented populations is exacerbated by drift and selection|url=http://dx.doi.org/10.1111/j.1420-9101.2006.01263.x|journal=Journal of Evolutionary Biology|volume=20|issue=2|pages=534–542|doi=10.1111/j.1420-9101.2006.01263.x|pmid=17305819|s2cid=1324102|issn=1010-061X}}</ref>
* {{Cite journal |last1=Brunet|first1=Johanne |last2=Larson-Rabin|first2=Zachary |last3=Stewart|first3=Christy M. |date=2012-06 |title=The Distribution of Genetic Diversity Within and Among Populations of the Rocky Mountain Columbine: The Impact of Gene Flow, Pollinators, and Mating System |url=http://dx.doi.org/10.1086/665263 |journal=International Journal of Plant Sciences |volume=173 |issue=5 |pages=484–494 |doi=10.1086/665263 |issn=1058-5893 }}
* {{Cite journal |last1=Cheptou|first1=Pierre-Olivier |last2=Hargreaves|first2=Anna L. |last3=Bonte|first3=Dries |last4=Jacquemyn|first4=Hans |date=2017-01-19 |title=Adaptation to fragmentation: evolutionary dynamics driven by human influences|url=http://dx.doi.org/10.1098/rstb.2016.0037 |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=372 |issue=1712 |pages=20160037 |doi=10.1098/rstb.2016.0037 |pmid=27920382 |pmc=5182433 |issn=0962-8436 }}
* {{Cite journal |author=Christopher G. Eckert, Karen E. Samis, Stephen C. Lougheed |date=2008-03 |title=Genetic variation across species' geographical ranges: the central–marginal hypothesis and beyond |url=http://dx.doi.org/10.1111/j.1365-294x.2007.03659.x |journal=Molecular Ecology |volume=17 |issue=5 |pages=1170–1188 |doi=10.1111/j.1365-294x.2007.03659.x |pmid=18302683 |issn=0962-1083 }} [https://www.researchgate.net/publication/5549140_Genetic_variation_across_species'_geographical_ranges_The_central-marginal_hypothesis_and_beyond ResearchGate].
* {{Cite journal |last1=Hampe|first1=Arndt |last2=Petit|first2=Rémy J. |date=2005-03-07 |title=Conserving biodiversity under climate change: the rear edge matters |url=http://dx.doi.org/10.1111/j.1461-0248.2005.00739.x |journal=Ecology Letters |volume=8 |issue=5 |pages=461–467 |doi=10.1111/j.1461-0248.2005.00739.x |pmid=21352449 |issn=1461-023X }}
* {{Cite journal |last1=Holt|first1=Robert D. |last2=Gomulkiewicz|first2=Richard |date=1997-03 |title=How Does Immigration Influence Local Adaptation? A Reexamination of a Familiar Paradigm |url=http://dx.doi.org/10.1086/286005 |journal=The American Naturalist |volume=149 |issue=3 |pages=563–572 |doi=10.1086/286005 |issn=0003-0147 }}
* Jing Hou, Anne Friedrich, Jacky de Montigny, Joseph Schacherer: [https://www.cell.com/current-biology/fulltext/S0960-9822(14)00385-6 Chromosomal Rearrangements as a Major Mechanism in the Onset of Reproductive Isolation in ''Saccharomyces cerevisiae'']. In: CurrentBiology, Band 24, Nr.&nbsp;10, S.&nbsp;1153–1159, 19. Mai 2014; [[doi:10.1016/j.cub.2014.03.063]], PMID 24814147, {{PMC|4067053}}.
* {{Cite journal|last1=Marchelli|first1=Paula |last2=Gallo|first2=Leonardo A, |date=2001-09 |title=Genetic diversity and differentiation in a southern beech subjected to introgressive hybridization |url=http://dx.doi.org/10.1046/j.1365-2540.2001.00882.x |journal=Heredity |volume=87 |issue=3 |pages=284–293 |doi=10.1046/j.1365-2540.2001.00882.x |pmid=11737275 |issn=0018-067X }}
* {{Cite journal |last1=Peterson|first1=Merrill A. |last2=Denno|first2=Robert F. |date=1998-09 |title=The Influence of Dispersal and Diet Breadth on Patterns of Genetic Isolation by Distance in Phytophagous Insects |url=http://dx.doi.org/10.1086/286180 |journal=The American Naturalist |volume=152 |issue=3 |pages=428–446 |doi=10.1086/286180 |pmid=18811450 |issn=0003-0147 }}
* {{Cite journal |last1=Provan|first1=Jim |last2=Maggs|first2=Christine A. |date=2011-05-18 |title=Unique genetic variation at a species' rear edge is under threat from global climate change |url=http://dx.doi.org/10.1098/rspb.2011.0536 |journal=Proceedings of the Royal Society B: Biological Sciences |volume=279 |issue=1726 |pages=39–47 |doi=10.1098/rspb.2011.0536 |pmid=21593035| pmc=3223643 |issn=0962-8452}}
* {{Cite journal |last1=Sexton|first1=Jason P. |last2=Hangartner|first2=Sandra B. |last3=Hoffmann|first3=Ary A. |title=Genetic Isolation by Environment or Distance: Which Pattern of Gene Flow is Most Common? |date=2014-01 |url=https://onlinelibrary.wiley.com/doi/10.1111/evo.12258 |journal=Evolution |language=en |volume=68 |issue=1 |pages=1–15 |doi=10.1111/evo.12258 |pmid=24111567 }}</ref>
* Chau-Ti Ting, Shun-Chern Tsaur, Mao-Lien Wu, Chung-I Wu: [https://www.science.org/doi/10.1126/science.282.5393.1501 A rapidly evolving homeobox at the site of a hybrid sterility gene]. In: Science, Band 282, Nr.&nbsp;5393, 20. November 1998, S.&nbsp;1501–1504; [[doi:10.1126/science.282.5393.1501]], PMID 9822383.
* {{Cite journal| last1=Tóth|first1=Endre Gy |last2=Tremblay|first2=Francine |last3=Housset|first3=Johann M. |last4=Bergeron |first4=Yves |last5=Carcaillet|first5=Christopher |date=2019-10-17 |title=Geographic isolation and climatic variability contribute to genetic differentiation in fragmented populations of the long-lived subalpine conifer Pinus cembra L. in the western Alps |url=http://dx.doi.org/10.1186/s12862-019-1510-4 |journal=BMC Evolutionary Biology |volume=19 |issue=1 |pages=190 |doi=10.1186/s12862-019-1510-4 |pmid=31623551 |pmc=6798344 |issn=1471-2148 }}


== Siehe auch ==
=== Genetic isolation in sympatric species ===
* [[Isolierte Sprache]]
Adaptation to diverse positions climatic conditions could be a significant source of genetic differences and isolation among populations. Pleiotropic induced sexual selection between individuals of these genetically diverse populations can be induced by biological features selected in each habitat. This circumstance could make sympatric speciation easier. For example, successful host transitions in phytophagous insects provide some of the most compelling evidence for ecological diversification in sympatric speciation.<ref>{{Cite journal|last1=Thomas|first1=Yan|last2=Bethenod|first2=Marie-Thérèse|last3=Pelozuelo|first3=Laurent|last4=Frérot|first4=Brigitte|last5=Bourguet|first5=Denis|title=Genetic Isolation Between Two Sympatric Host-Plant Races of the European Corn Borer, Ostrinia Nubilalis Hubner I. Sex Pheromone, Moth Emergence Timing, and Parasitism|date=February 2003|url=http://dx.doi.org/10.1111/j.0014-3820.2003.tb00261.x|journal=Evolution|volume=57|issue=2|pages=261–273|doi=10.1111/j.0014-3820.2003.tb00261.x|pmid=12683523|s2cid=221734366|issn=0014-3820}}</ref>


== Einzelnachweise ==
=== Genetic isolate and the burden of genetic diversity ===
<references>
Species with enormous ecological amplitudes, on the whole, have a lot of genetic diversity. More specialized species with small ecological amplitude and frequency, on the other hand, have minimal genetic diversity. Inbreeding depressions may pose the greatest threat to species with moderate habitat demands and substantial genetic diversity.<ref>{{Cite journal|last1=Habel|first1=Jan Christian|last2=Schmitt|first2=Thomas|date=March 2012|title=The burden of genetic diversity|url=http://dx.doi.org/10.1016/j.biocon.2011.11.028|journal=Biological Conservation|volume=147|issue=1|pages=270–274|doi=10.1016/j.biocon.2011.11.028|issn=0006-3207}}</ref>


<ref name="NGS">Ilmari Karonen (Illustration) ''et&nbsp;al.'': [https://www.nationalgeographic.org/encyclopedia/speciation/ Speciation]. [[National Geographic Society]] (NGS), Re&#x200B;source Library. Zugriffsdatum: 18. März 2022.</ref>
=== The Influence of dispersal and diet on patterns of genetic isolation ===
Gene flow across populations is commonly thought to be a key role in the evolution of both local adaptations and speciation. It is necessary to assess genetic separation by distance to determine the impacts of dispersal ability and food breadth on genetic population structure. Strong dispersers have a mild IBD (isolation by distance) because of the homogenizing effects of gene flow, whereas stationary species have limited gene flow, which permits nearly all populations to isolate. Genetic uniformity is achieved at small geographical scales in intermediate dispersers, whereas limited dispersal increases genetic variability across vast distances. IBD is also thought to rise with decreasing food breadth and no other pattern, putting the theory that specialization promotes speciation by affecting population genetically subdivision to the test. In studies of IBD, the number of populations is more essential than the number of multiple alleles per locus.<ref>{{Cite journal|last1=Peterson|first1=Merrill A.|last2=Denno|first2=Robert F.|date=September 1998|title=The Influence of Dispersal and Diet Breadth on Patterns of Genetic Isolation by Distance in Phytophagous Insects|url=http://dx.doi.org/10.1086/286180|journal=The American Naturalist|volume=152|issue=3|pages=428–446|doi=10.1086/286180|pmid=18811450|s2cid=3497508|issn=0003-0147}}</ref>


<!-------------------------------------->
=== Current patterns of genetic isolation on islands ===
Individuals from several vegetation types on the island are genetically connected, demonstrating that ecological and climatic factors have a role in determining gene flow configurations on a small island. Climatic differentiation, as a single factor is included as separate variability, provides to decreases in immigration and reproduction in as many species belongs to a wide range of herbs families and with variable amounts of evolutionary understanding. The genetic structure of species on an isolated island is influenced by a range of environmental variables, with some species being influenced by single contours and others being influenced by many species. Sister species and congenerics have various contributing elements to isolation within species.<ref>{{Cite journal|last1=Haider|first1=Sylvia|last2=Kueffer|first2=Christoph|last3=Edwards|first3=Peter J.|last4=Alexander|first4=Jake M.|date=September 2012|title=Genetically based differentiation in growth of multiple non-native plant species along a steep environmental gradient|url=http://link.springer.com/10.1007/s00442-012-2291-2|journal=Oecologia|language=en|volume=170|issue=1|pages=89–99|doi=10.1007/s00442-012-2291-2|pmid=22434406|bibcode=2012Oecol.170...89H|s2cid=6346092|issn=0029-8549}}</ref>


<ref name="Arcos-Burgos2002">Mauricio Arcos-Burgos, Maximilian Muenke: [https://onlinelibrary.wiley.com/doi/abs/10.1034/j.1399-0004.2002.610401.x Genetics of population isolates]. In: Clinical Genetics, Band 61, Nr.&nbsp;4, S.&nbsp;233–247, 27. Mai 2002; [[doi:10.1034/j.1399-0004.2002.610401.x]], PMID 12030885.</ref>
== Advantages ==
In most situations, highly specialized species are constrained to a small portion of the accessible environment, characterized by extremely isolated populations.<ref>{{Cite journal|last1=Johansson|first1=Per|last2=Ehrlén|first2=Johan|date=April 2003|title=Influence of habitat quantity, quality and isolation on the distribution and abundance of two epiphytic lichens|url=http://dx.doi.org/10.1046/j.1365-2745.2003.00755.x|journal=Journal of Ecology|volume=91|issue=2|pages=213–221|doi=10.1046/j.1365-2745.2003.00755.x|issn=0022-0477}}</ref> This ecological specialization and consequently geographical constraint of indigenous populations is frequently accompanied by a reduction in gene flow, resulting in small population sizes and genetic differentiation. As a result, due to genetic isolation, such species can only survive if they are suited to minimal genetic isolation.<ref>{{Cite journal|last1=Kawamura|first1=Kouichi|last2=Kubota|first2=Masashi|last3=Furukawa|first3=Miki|last4=Harada|first4=Yasushi|date=2007-01-05|title=The genetic structure of endangered indigenous populations of the amago salmon, Oncorhynchus masou ishikawae, in Japan|url=http://dx.doi.org/10.1007/s10592-006-9271-1|journal=Conservation Genetics|volume=8|issue=5|pages=1163–1176|doi=10.1007/s10592-006-9271-1|s2cid=32130367|issn=1566-0621}}</ref><ref>{{Cite journal|last1=Besold|first1=Joachim|last2=Schmitt|first2=Thomas|last3=Tammaru|first3=Toomas|last4=Cassel-Lundhagen|first4=Anna|date=November 2008|title=Strong genetic impoverishment from the centre of distribution in southern Europe to peripheral Baltic and isolated Scandinavian populations of the pearly heath butterfly|url=http://dx.doi.org/10.1111/j.1365-2699.2008.01939.x|journal=Journal of Biogeography|volume=35|issue=11|pages=2090–2101|doi=10.1111/j.1365-2699.2008.01939.x|issn=0305-0270}}</ref> In the search for lethal genes, genetic isolates with a background of a small founding population, long-term isolation, and population bottlenecks are invaluable resources. Specific rare, monogenic disorders get enhanced, and families with numerous sick members become common enough to be employed in locus-identifying linkage analyses. Besides that, the vast majority of cases are caused by the same mutation, and diseased alleles expose linkage of disequilibrium with molecular markers over strong genetic distances, making disease locus recognition easier in small study samples with few individuals affected using a similarity search for a shared genotype. The presence of disequilibrium linkage in disease alleles enhances linkage analysis and aids in determining the precise position of disease locus on the genome sequence.<ref>{{Cite journal|last=Peltonen|first=Leena|date=1999-10-01|title=Positional Cloning of Disease Genes: Advantages of Genetic Isolates|url=http://dx.doi.org/10.1159/000022892|journal=Human Heredity|volume=50|issue=1|pages=66–75|doi=10.1159/000022892|pmid=10545759|s2cid=25810192|issn=0001-5652}}</ref>


<ref name="Bockelmann2003">{{Cite journal |last1=Bockelmann|first1=Anna-Christina |last2=Reusch|first2=Thorsten B.&nbsp;H. |last3=Bijlsma|first3=R. |last4=Bakker|first4=Jan P. |date=2003-02 |title=Habitat differentiation vs. isolation-by-distance: the genetic population structure of Elymus athericus in European salt marshes |url=http://dx.doi.org/10.1046/j.1365-294x.2003.01706.x |journal=Molecular Ecology |volume=12 |issue=2 |pages=505–515 |doi=10.1046/j.1365-294x.2003.01706.x |pmid=12535100 |issn=0962-1083 }}</ref>
== Disadvantages ==
Many species fall somewhere between generalist and specialist on the generalist specialist range. Such species generally exhibit moderate environmental specialization, being neither pure generalists nor pure specialists, resulting in fluid changes that must be subjective when categorizing species. Despite their considerable habitat specialization, environmentally transitional species generally do not exhibit the low genetic diversity seen in pure specialists, but instead, exhibit species-specific genetic differences on the scale with generalists. These taxa, on the other hand, are categorized as far more endangered as their degree of specialization would suggest. This scenario can be harmful in the progression of population decline and may be one of the promoters of extinction in this instance, owing to the genomic instability of populations and unpredictable aggregation of detrimental genes.<ref>{{Cite journal|last1=Habel|first1=Jan Christian|last2=Schmitt|first2=Thomas|date=March 2012|title=The burden of genetic diversity|url=http://dx.doi.org/10.1016/j.biocon.2011.11.028|journal=Biological Conservation|volume=147|issue=1|pages=270–274|doi=10.1016/j.biocon.2011.11.028|issn=0006-3207}}</ref>


<ref name="Brown2007">{{cite journal |author=David M. Brown, Rick A. Brenneman, Klaus-Peter Koepfli, John P. Pollinger, Borja Milá , Nicholas J. Georgiadis, Edward E. Louis Jr, Gregory F. Grether, David K. Jacobs, Robert K. Wayne| date=2007-12-21 |title=Extensive population genetic structure in the giraffe |journal=BMC Biology |volume=5 |issue=1 |pages=57 |doi=10.1186/1741-7007-5-57 |pmid=18154651 |pmc=2254591 |url=https://bmcbiol.biomedcentral.com/articles/10.1186/1741-7007-5-57 }}</ref>
'''''Example:'''''


<ref name="Habel2012">{{Cite journal |last1=Habel|first1=Jan Christian |last2=Schmitt|first2=Thomas |date=2012-03 |title=The burden of genetic diversity |url=http://dx.doi.org/10.1016/j.biocon.2011.11.028 |journal=Biological Conservation |volume=147 |issue=1 |pages=270–274 |doi=10.1016/j.biocon.2011.11.028 |issn=0006-3207 }}</ref>
'''Genetic isolation in the cyclic rodent ''Microtus avails'''''


<ref name="Haider2012">{{Cite journal |last1=Haider|first1=Sylvia |last2=Kueffer|first2=Christoph |last3=Edwards|first3=Peter J. |last4=Alexander|first4=Jake M. |date=2012-09 |title=Genetically based differentiation in growth of multiple non-native plant species along a steep environmental gradient |url=http://link.springer.com/10.1007/s00442-012-2291-2 |journal=Oecologia |language=en |volume=170 |issue=1 |pages=89–99 |doi=10.1007/s00442-012-2291-2 |pmid=22434406 |bibcode=2012Oecol.170...89H |issn=0029-8549 }}</ref>
''Microtus arvalis,'' a small-sized mouse with short dispersal ranges that achieves relatively high richness, has been used as a model to investigate the effects of roads on genetic diversity and organization in fragmented and competitive habitats. The species' remarkable colonization potential has been observed in recent decades.,<ref>{{Cite journal|last1=Luque-Larena|first1=Juan J.|last2=Mougeot|first2=Francois|last3=Viñuela|first3=Javier|last4=Jareño|first4=Daniel|last5=Arroyo|first5=Leticia|last6=Lambin|first6=Xavier|last7=Arroyo|first7=Beatriz|date=August 2013|title=Recent large-scale range expansion and outbreaks of the common vole (Microtus arvalis) in NW Spain|url=http://dx.doi.org/10.1016/j.baae.2013.04.006|journal=Basic and Applied Ecology|volume=14|issue=5|pages=432–441|doi=10.1016/j.baae.2013.04.006|issn=1439-1791}}</ref> making it particularly well suited to studying small mammal dispersion strategies over short periods. Furthermore, these mouse populations achieve high local abundances and may endure significant population fluctuations in a few years, with well-defined periods.<ref>{{Cite journal|last1=Gerlach|first1=Gabriele|last2=Musolf|first2=Kerstin|date=2000-08-15|title=Fragmentation of Landscape as a Cause for Genetic Subdivision in Bank Voles|url=http://dx.doi.org/10.1046/j.1523-1739.2000.98519.x|journal=Conservation Biology|volume=14|issue=4|pages=1066–1074|doi=10.1046/j.1523-1739.2000.98519.x|issn=0888-8892}}</ref> In comparison to what has been reported for other morphologically similar small mammals with more reasonably expected populations, this species' cyclic variation in population size makes it particularly fascinating to explore the possible sensitivity to road barriers.<ref>{{Cite journal|last1=Ascensão|first1=Fernando|last2=Mata|first2=Cristina|last3=Malo|first3=Juan E.|last4=Ruiz-Capillas|first4=Pablo|last5=Silva|first5=Catarina|last6=Silva|first6=André P.|last7=Santos-Reis|first7=Margarida|last8=Fernandes|first8=Carlos|date=2016-03-15|title=Disentangle the Causes of the Road Barrier Effect in Small Mammals through Genetic Patterns|journal=PLOS ONE|volume=11|issue=3|pages=e0151500|doi=10.1371/journal.pone.0151500|pmid=26978779|pmc=4792435|bibcode=2016PLoSO..1151500A|issn=1932-6203|doi-access=free}}</ref> In a system with considerable population size changes, the lowest population size experiences the highest amounts of genetic drift. As a result, demographic bottlenecks are likely to have a large impact on genetic isolations and variations, reducing variability within populations while increasing variance between them. The enormous population size and gene flow at the highest stages, on the other hand, may lessen the effects of drift and bottlenecks, however, it may take many generations for the species to achieve new equilibrium values.<ref>{{Cite journal|last1=Parra|first1=Guido J.|last2=Cagnazzi|first2=Daniele|last3=Jedensjö|first3=Maria|last4=Ackermann|first4=Corinne|last5=Frere|first5=Celine|last6=Seddon|first6=Jennifer|last7=Nikolic|first7=Natacha|last8=Krützen|first8=Michael|date=April 2018|title=Low genetic diversity, limited gene flow and widespread genetic bottleneck effects in a threatened dolphin species, the Australian humpback dolphin|url=http://dx.doi.org/10.1016/j.biocon.2017.12.028|journal=Biological Conservation|volume=220|pages=192–200|doi=10.1016/j.biocon.2017.12.028|issn=0006-3207}}</ref>


<ref name="Jiang2017">{{Cite journal |last1=Jiang|first1=Xiao-Long |last2=An|first2=Miao |last3=Zheng|first3=Si-Si |last4=Deng|first4=Min |last5=Su|first5=Zhi-Hao |date=2017-12-27 |title=Geographical isolation and environmental heterogeneity contribute to the spatial genetic patterns of Quercus kerrii (Fagaceae) |url=http://dx.doi.org/10.1038/s41437-017-0012-7 |journal=Heredity |volume=120 |issue=3 |pages=219–233 |doi=10.1038/s41437-017-0012-7 |pmid=29279604 |pmc=5836588 |issn=0018-067X }}</ref>
== See also ==
* [[Language isolate]]
* [[Linkage disequilibrium]]


<ref name="Kreyling2014">{{Cite journal |last1=Kreyling|first1=Juergen |last2=Buhk|first2=Constanze |last3=Backhaus|first3=Sabrina |last4=Hallinger|first4=Martin |last5=Huber|first5=Gerhard |last6=Huber|first6=Lukas |last7=Jentsch|first7=Anke |last8=Konnert|first8=Monika |last9=Thiel|first9=Daniel |last10=Wilmking|first10=Martin |last11=Beierkuhnlein|first11=Carl |date=2014-02-07 |title=Local adaptations to frost in marginal and central populations of the dominant forest tree Fagus sylvatica L. as affected by temperature and extreme drought in common garden experiments |url=http://dx.doi.org/10.1002/ece3.971 |journal=Ecology and Evolution |volume=4 |issue=5 |pages=594–605 |doi=10.1002/ece3.971 |pmid=25035801 |pmc=4098140 |issn=2045-7758 }}</ref>
==References==
{{Reflist}}


<ref name="AD-Gc">Sarah Maisano; Tanya Dewey (Hrsg.): [https://animaldiversity.org/accounts/Giraffa_camelopardalis/ Giraffa camelopardalis – giraffe]. Auf: Animal Diversity Web (ADW), [[University of Michigan]], Ecology and Evolutionary Biology, Museum of Zoology, 2020.</ref>
{{DEFAULTSORT:Genetic Isolate}}

[[Category:Speciation]]
<ref name="Mayr1970">[[Ernst Mayr]]: [https://www.hup.harvard.edu/catalog.php?isbn=9780674690134 Populatiomns, species, and evolution – An abridgment of Animal species and evolution]. The Belknap Press of Harvard University Press, Cambridge, Massachusetts & London, England, 1. Januar 1970, ISBN 0-674-69013-3.</ref>

<ref name="Campbell2011">Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson: [https://www.pearson.com/us/higher-education/product/Reece-Campbell-Biology-9th-Edition/9780321558237.html Campbell Biology], 9th edition, Pearson 2011, S.&nbsp;489–491</ref>

<ref name="Sterling2012">{{Cite journal |last1=Sterling |first1=Ken A. |last2=Reed |first2=David H. |last3=Noonan |first3=Brice P. |last4=Warren |first4=Melvin L. |date=2012-03-28 |title=Genetic effects of habitat fragmentation and population isolation on Etheostoma raneyi (Percidae) |url=http://dx.doi.org/10.1007/s10592-012-0335-0 |journal=Conservation Genetics |volume=13 |issue=3 |pages=859–872 |doi=10.1007/s10592-012-0335-0 |issn=1566-0621 }}</ref>

<ref name="Thomas2003">{{Cite journal |last1=Thomas|first1=Yan |last2=Bethenod|first2=Marie-Thérèse |last3=Pelozuelo|first3=Laurent |last4=Frérot|first4=Brigitte |last5=Bourguet|first5=Denis |title=Genetic Isolation Between Two Sympatric Host-Plant Races of the European Corn Borer, Ostrinia Nubilalis Hubner I. Sex Pheromone, Moth Emergence Timing, and Parasitism |date=2003-02 |url=http://dx.doi.org/10.1111/j.0014-3820.2003.tb00261.x |journal=Evolution |volume=57 |issue=2 |pages=261–273 |doi=10.1111/j.0014-3820.2003.tb00261.x |pmid=12683523 |issn=0014-3820 }}</ref>

<ref name="Willi2007">{{Cite journal|author=Yvonne Willi, Josh Van Buskirk, Bernhard Schmid, Markus Fischer |date=2007-03 |title=Genetic isolation of fragmented populations is exacerbated by drift and selection |url=http://dx.doi.org/10.1111/j.1420-9101.2006.01263.x |journal=Journal of Evolutionary Biology |volume=20 |issue=2 |pages=534–542 |doi=10.1111/j.1420-9101.2006.01263.x |pmid=17305819 |issn=1010-061X }}</ref>

</references>

[[Kategorie:Ausbreitungsökologie]]
[[Kategorie:Evolutionsökologie]]

Version vom 20. März 2022, 01:07 Uhr

Ein genetisches Isolat ist eine Population von Organismen, die eine geringe oder keine genetische Vermischung mit anderen Organismen derselben Art aufweist. In einigen Fällen kann es zur Artbildung (Speziation) kommen, aber das muss nicht unbedingt der Fall sein. Der Begriff bezieht sich auf gewöhnlich auf Organismen mit geschlechtlicher Fortpflanzung, wie sie gewöhnlich bei Eukaryoten, insbesondere Tieren und Pflanzen, vorkommt. Allgemein ist Voraussetzung, dass die Individuen einer Population normalerweise im ständigen Austausch (Genfluss) ihrer genetischen Information stehen (etwa durch Rekombination und/oder Reassortment). Genetische oder reproduktive Isolation ist dann das Ausbleiben dieser Vermischung durch Unterbrechung des Genflusses.[1][2][3]

Ursachen genetischer Isolation

Genetische Isolate können auf verschiedene Weise zur Entstehung neuer Arten führen:[1][2][3]

  • Allopatrische Speziation: Bei dieser werden zwei Populationen derselben Art durch eine äußere Barriere geografisch voneinander getrennt und entwickeln eine intrinsische (genetische) reproduktive Isolation.
  • Peripatrische Speziation: Hier wird eine kleine Gruppe einer Population von der Hauptpopulation getrennt und erfährt eine genetische Drift infolge von Selektionsdruck.
  • Parapatrische Speziation: Die Kerngebiete der Zonen zweier unterschiedlicher Populationen sind hier getrennt, in ihren Randgebieten kommt es aber zu regionalen Überschneidungen. Die teilweise Trennung wird ebenfalls durch die Geographie garantiert, sodass Individuen jeder Population von Zeit zu Zeit miteinander in Kontakt kommen können. Die Auswahl nach bestimmten Verhaltensweisen oder Mechanismen (beispielsweise Im Balzverhalten oder der genauen Melodie des Vogelgesangs) kann die Fortpflanzung zwischen den beiden Gruppen verhindern.
  • Sympatrische Speziation: Dies ist eine umstrittene Artbildungsmethode, bei der Arten sich zweiteilen, während sie denselben Ort bewohnen.

Die ersten beiden Szenarien führen zur geografischen Isolation, das letzte zur ökologischen Isolation, das dritte stellt eine Mischform dar.

Zu den menschlichen Einflüssen auf genetische Isolate gehört eine genetische Durchmischung von Haustieren begrenzende Rassezucht (Beispiele: Hundezucht und Kaninchenzucht); analog die Zucht neuer Sorten von Nutz- und Kulturpflanzen (Beispiele: Kartoffelsorten, Rosensorten und Weizensorten – nicht -arten).

Isolate und Subspezies aufgrund allopatrischer Speziation bei Giraffen

Wenn sich eine Art in zwei verschiedene Gruppen aufspaltet, die voneinander isoliert sind, wird dies als allopatrische Speziation (Artbildung) bezeichnet.[4] Die Giraffe (Giraffa camelopardalis),[5] ist ein Beispiel für die allopatrische (Unter-)Artbildung, wie sie durch die genetische Isolierung einer Population entsteht. Mehrere Giraffenkladen weisen Unterschiede in ihrer mitochondrialen DNA (mtDNA) auf, die zwischen verschiedenen Regionen Afrikas variieren. Diese Unterschiede gehen auf die Mitte des Pleistozäns zurück und fallen mit der genetischen Isolation aufgrund klimatischer und geografischer Trennungen innerhalb der Populationen zusammen, was die Entwicklung und Unterspeziation der verschiedenen Unterarten der Giraffe und die Unterschiede in ihrer Farbmuster ermöglichte.[6]

Genetische Isolate beim Jetztmenschen

Genetische Isolate beim Jetztmenschen (Homo sapiens) selbst findet man bei Gemeinschaften, die abgeschieden von anderen leben, wie auf Tristan da Cunha oder den Pitcairn-Inseln. Weitaus größere und weniger abgelegene menschliche genetische Isolate sind Völker wie in Europa die Sarden oder auch die Finnen, die Ureinwohner Sardiniens bzw. Finnlands.[1] Beispiele in Asien sind

Isolation und Bedrohung durch Aussterben

Isolation in Kombination mit abnehmender Lebensraumqualität und Populationsdichte kann mit großer Wahrscheinlichkeit zum Zusammenbruch einer Population und schließlich zu deren Aussterben führen.[7] Es ist erwiesen, dass die zufällige Mutationsrate, Drift, hohe Inzuchtqouten, eingeschränkter Genfluss und regionales Aussterben mit der Isolation zunehmen. Unterschiedliche klimatische Bedingungen, wie geografische Klimaveränderungen, können zu Belastungen führen, die die genetische Zusammensetzung einer Art drastisch verändern und durch regional stark unterschiedliche Selektionsprozesse zu Unterschieden im Genpool führen,[8] sowie zu einer verstärkten genetischen Isolation zwischen Populationen in einer heterogenen Landschaft.[9] Umweltheterogenität wurde in der Vergangenheit als wichtige Quelle für genetische Variationen und Unterschiede aufgrund von Isolation identifiziert. Genetische Isolation und die Auswirkungen regional unterschiedlicher Lebensumstände können als Beleg für eine diversifizierende Selektion angeführt werden, die über das gesamte Genom hinweg wirkt und auch offensichtlich neutrale Gene umfasst. Dies kann zur Vorhersage langfristiger Auswirkungen von Umweltfaktoren auf die genetische Vielfalt und die genetische Isolation herangezogen werden.[10]

Stark fragmentierte Populationen

Der Zusammenhang zwischen der Statistik genetischer Unterschiede und der Populationsgröße wurde bisher wissenschaftlich kaum beachtet, obwohl kleine Populationen eine geringere genetische Variation an Markerloci aufweisen. Es ließ sich zeigen, dass in kleineren fragmentierten Meta-Populationen sowohl die neutrale als auch die quantifizierbare genetische Variation reduziert ist und sowohl die Drift als auch die selektionsbedingte Veränderungen verstärkt werden.[11]

Sympatrische Spezies durch Klimaeinflüsse

Die Anpassung an unterschiedliche klimatische Bedingungen kann eine wichtige Quelle für genetische Unterschiede und die Isolation von Populationen sein. So liefern beispielsweise erfolgreiche Wirtswechsel bei Pflanzenschädlingen unter den Insekten einige der überzeugendsten Beweise für ökologische Diversifizierung bei sympatrischer Artbildung[12]

Genetische Isolate und die Auswirkungen der genetischen Vielfalt

Arten mit enormen ökologischen Bandbreiten weisen im Allgemeinen eine große genetische Vielfalt auf. Stärker spezialisierte Arten mit geringer ökologischer Bandbreite und Häufigkeit haben dagegen nur eine geringe genetische Vielfalt. Inzuchtdepressionen, d. h. Verringerung der genetischen Vielfalt (im Genpool) aufgrund von Inzucht stellen vielleicht die größte Bedrohung für Arten mit mäßigen Lebensraumansprüchen und großer genetischer Vielfalt dar.[13]

Genetische Isolate auf Inseln

Das Phänomen der genetischen Isolation unter den speziellen Bedingungen mehr oder weniger kleiner Inseln wurde von Haider et al. 2012 untersucht,[14] siehe auch Inselverzwergung.

Literatur

Siehe auch

Einzelnachweise

  1. ↑ a b c Mauricio Arcos-Burgos, Maximilian Muenke: Genetics of population isolates. In: Clinical Genetics, Band 61, Nr. 4, S. 233–247, 27. Mai 2002; doi:10.1034/j.1399-0004.2002.610401.x, PMID 12030885.
  2. ↑ a b Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson: Campbell Biology, 9th edition, Pearson 2011, S. 489–491
  3. ↑ a b Ernst Mayr: Populatiomns, species, and evolution – An abridgment of Animal species and evolution. The Belknap Press of Harvard University Press, Cambridge, Massachusetts & London, England, 1. Januar 1970, ISBN 0-674-69013-3.
  4. ↑ Ilmari Karonen (Illustration) et al.: Speciation. National Geographic Society (NGS), Re​source Library. Zugriffsdatum: 18. März 2022.
  5. ↑ Sarah Maisano; Tanya Dewey (Hrsg.): Giraffa camelopardalis – giraffe. Auf: Animal Diversity Web (ADW), University of Michigan, Ecology and Evolutionary Biology, Museum of Zoology, 2020.
  6. ↑ David M. Brown, Rick A. Brenneman, Klaus-Peter Koepfli, John P. Pollinger, Borja Milá , Nicholas J. Georgiadis, Edward E. Louis Jr, Gregory F. Grether, David K. Jacobs, Robert K. Wayne: Extensive population genetic structure in the giraffe. In: BMC Biology. 5. Jahrgang, Nr. 1, 21. Dezember 2007, S. 57, doi:10.1186/1741-7007-5-57, PMID 18154651, PMC 2254591 (freier Volltext) – (biomedcentral.com).
  7. ↑ Ken A. Sterling, David H. Reed, Brice P. Noonan, Melvin L. Warren: Genetic effects of habitat fragmentation and population isolation on Etheostoma raneyi (Percidae). In: Conservation Genetics. 13. Jahrgang, Nr. 3, 28. März 2012, ISSN 1566-0621, S. 859–872, doi:10.1007/s10592-012-0335-0 (doi.org).
  8. ↑ Juergen Kreyling, Constanze Buhk, Sabrina Backhaus, Martin Hallinger, Gerhard Huber, Lukas Huber, Anke Jentsch, Monika Konnert, Daniel Thiel, Martin Wilmking, Carl Beierkuhnlein: Local adaptations to frost in marginal and central populations of the dominant forest tree Fagus sylvatica L. as affected by temperature and extreme drought in common garden experiments. In: Ecology and Evolution. 4. Jahrgang, Nr. 5, 7. Februar 2014, ISSN 2045-7758, S. 594–605, doi:10.1002/ece3.971, PMID 25035801, PMC 4098140 (freier Volltext) – (doi.org).
  9. ↑ Anna-Christina Bockelmann, Thorsten B. H. Reusch, R. Bijlsma, Jan P. Bakker: Habitat differentiation vs. isolation-by-distance: the genetic population structure of Elymus athericus in European salt marshes. In: Molecular Ecology. 12. Jahrgang, Nr. 2, Februar 2003, ISSN 0962-1083, S. 505–515, doi:10.1046/j.1365-294x.2003.01706.x, PMID 12535100 (doi.org).
  10. ↑ Xiao-Long Jiang, Miao An, Si-Si Zheng, Min Deng, Zhi-Hao Su: Geographical isolation and environmental heterogeneity contribute to the spatial genetic patterns of Quercus kerrii (Fagaceae). In: Heredity. 120. Jahrgang, Nr. 3, 27. Dezember 2017, ISSN 0018-067X, S. 219–233, doi:10.1038/s41437-017-0012-7, PMID 29279604, PMC 5836588 (freier Volltext) – (doi.org).
  11. ↑ Yvonne Willi, Josh Van Buskirk, Bernhard Schmid, Markus Fischer: Genetic isolation of fragmented populations is exacerbated by drift and selection. In: Journal of Evolutionary Biology. 20. Jahrgang, Nr. 2, März 2007, ISSN 1010-061X, S. 534–542, doi:10.1111/j.1420-9101.2006.01263.x, PMID 17305819 (doi.org).
  12. ↑ Yan Thomas, Marie-Thérèse Bethenod, Laurent Pelozuelo, Brigitte Frérot, Denis Bourguet: Genetic Isolation Between Two Sympatric Host-Plant Races of the European Corn Borer, Ostrinia Nubilalis Hubner I. Sex Pheromone, Moth Emergence Timing, and Parasitism. In: Evolution. 57. Jahrgang, Nr. 2, Februar 2003, ISSN 0014-3820, S. 261–273, doi:10.1111/j.0014-3820.2003.tb00261.x, PMID 12683523 (doi.org).
  13. ↑ Jan Christian Habel, Thomas Schmitt: The burden of genetic diversity. In: Biological Conservation. 147. Jahrgang, Nr. 1, März 2012, ISSN 0006-3207, S. 270–274, doi:10.1016/j.biocon.2011.11.028 (doi.org).
  14. ↑ Sylvia Haider, Christoph Kueffer, Peter J. Edwards, Jake M. Alexander: Genetically based differentiation in growth of multiple non-native plant species along a steep environmental gradient. In: Oecologia. 170. Jahrgang, Nr. 1, September 2012, ISSN 0029-8549, S. 89–99, doi:10.1007/s00442-012-2291-2, PMID 22434406, bibcode:2012Oecol.170...89H (englisch, springer.com).
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