Evolution Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! === Speciation === {{main|Speciation}} {{further|Assortative mating|Panmixia}} [[File:Speciation modes edit.svg|left|thumb|upright=1.6|The four geographic modes of [[speciation]]]] Speciation is the process where a species diverges into two or more descendant species.<ref name="Gavrilets">{{cite journal |last=Gavrilets |first=Sergey |date=October 2003 |title=Perspective: models of speciation: what have we learned in 40 years? |journal=Evolution |volume=57 |issue=10 |pages=2197–2215 |doi=10.1554/02-727 |pmid=14628909 |s2cid=198158082 }}</ref> There are multiple ways to define the concept of "species". The choice of definition is dependent on the particularities of the species concerned.<ref name="Queiroz">{{cite journal |last=de Queiroz |first=Kevin |date=3 May 2005 |title=Ernst Mayr and the modern concept of species |journal=PNAS |volume=102 |issue=Suppl. 1 |pages=6600–6607 |bibcode=2005PNAS..102.6600D |doi=10.1073/pnas.0502030102 |pmc=1131873 |pmid=15851674 |doi-access=free }}</ref> For example, some species concepts apply more readily toward sexually reproducing organisms while others lend themselves better toward asexual organisms. Despite the diversity of various species concepts, these various concepts can be placed into one of three broad philosophical approaches: interbreeding, ecological and phylogenetic.<ref name="Ereshefsky92">{{cite journal |last=Ereshefsky |first=Marc |author-link=Marc Ereshefsky |date=December 1992 |title=Eliminative pluralism |url=https://archive.org/details/sim_philosophy-of-science_1992-12_59_4/page/671 |journal=[[Philosophy of Science (journal)|Philosophy of Science]] |volume=59 |issue=4 |pages=671–690 |doi=10.1086/289701 |jstor=188136|s2cid=224829314 }}</ref> The Biological Species Concept (BSC) is a classic example of the interbreeding approach. Defined by evolutionary biologist [[Ernst Mayr]] in 1942, the BSC states that "species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups."<ref>{{harvnb|Mayr|1942|p=120}}</ref> Despite its wide and long-term use, the BSC like other species concepts is not without controversy, for example, because genetic recombination among prokaryotes is not an intrinsic aspect of reproduction;<ref>{{cite journal |last1=Fraser |first1=Christophe |last2=Alm |first2=Eric J. |last3=Polz |first3=Martin F. |last4=Spratt |first4=Brian G. |last5=Hanage |first5=William P. |s2cid=15763831 |date=6 February 2009 |title=The Bacterial Species Challenge: Making Sense of Genetic and Ecological Diversity |journal=Science |volume=323 |issue=5915 |pages=741–746 |bibcode=2009Sci...323..741F |doi=10.1126/science.1159388 |pmid=19197054 |display-authors=3}}</ref> this is called the [[species problem]].<ref name="Queiroz" /> Some researchers have attempted a unifying monistic definition of species, while others adopt a pluralistic approach and suggest that there may be different ways to logically interpret the definition of a species.<ref name="Queiroz" /><ref name="Ereshefsky92" /> [[Reproductive isolation|Barriers to reproduction]] between two diverging sexual populations are required for the populations to become new species. Gene flow may slow this process by spreading the new genetic variants also to the other populations. Depending on how far two species have diverged since their [[most recent common ancestor]], it may still be possible for them to produce offspring, as with horses and donkeys mating to produce [[mule]]s.<ref>{{cite journal |last=Short |first=Roger Valentine |date=October 1975 |title=The contribution of the mule to scientific thought |journal=Journal of Reproduction and Fertility. Supplement |issue=23 |pages=359–364 |oclc=1639439 |pmid=1107543}}</ref> Such hybrids are generally [[infertile]]. In this case, closely related species may regularly interbreed, but hybrids will be selected against and the species will remain distinct. However, viable hybrids are occasionally formed and these new species can either have properties intermediate between their parent species, or possess a totally new phenotype.<ref>{{cite journal |last1=Gross |first1=Briana L. |last2=Rieseberg |first2=Loren H. |date=May–June 2005 |title=The Ecological Genetics of Homoploid Hybrid Speciation |journal=Journal of Heredity |volume=96 |issue=3 |pages=241–252 |doi=10.1093/jhered/esi026 |issn=0022-1503 |pmc=2517139 |pmid=15618301}}</ref> The importance of hybridisation in producing [[hybrid speciation|new species]] of animals is unclear, although cases have been seen in many types of animals,<ref>{{cite journal |last1=Burke |first1=John M. |last2=Arnold |first2=Michael L. |s2cid=26683922 |date=December 2001 |title=Genetics and the fitness of hybrids |journal=[[Annual Review of Genetics]] |volume=35 |pages=31–52 |doi=10.1146/annurev.genet.35.102401.085719 |issn=0066-4197 |pmid=11700276}}</ref> with the [[gray tree frog]] being a particularly well-studied example.<ref>{{cite journal |last=Vrijenhoek |first=Robert C. |s2cid=11657663 |date=4 April 2006 |title=Polyploid Hybrids: Multiple Origins of a Treefrog Species |journal=Current Biology |volume=16 |issue=7 |pages=R245–R247 |doi=10.1016/j.cub.2006.03.005 |issn=0960-9822 |pmid=16581499|doi-access=free |bibcode=2006CBio...16.R245V }}</ref> Speciation has been observed multiple times under both [[Laboratory experiments of speciation|controlled laboratory conditions]] and in nature.<ref>{{cite journal |last1=Rice |first1=William R. |last2=Hostert |first2=Ellen E. |date=December 1993 |title=Laboratory Experiments on Speciation: What Have We Learned in 40 Years? |journal=Evolution |volume=47 |issue=6 |pages=1637–1653 |doi=10.1111/j.1558-5646.1993.tb01257.x |pmid=28568007 |issn=0014-3820|jstor=2410209 |s2cid=42100751 }} * {{cite journal |last1=Jiggins |first1=Chris D. |last2=Bridle |first2=Jon R. |date=March 2004 |title=Speciation in the apple maggot fly: a blend of vintages? |journal=Trends in Ecology & Evolution |volume=19 |issue=3 |pages=111–114 |doi=10.1016/j.tree.2003.12.008 |pmid=16701238 |issn=0169-5347 |ref=none}} * {{cite web |url=http://www.talkorigins.org/faqs/faq-speciation.html |title=Observed Instances of Speciation |last=Boxhorn |first=Joseph |date=1 September 1995 |website=TalkOrigins Archive |publisher=The TalkOrigins Foundation, Inc. |location=Houston, Texas |access-date=26 December 2008 |url-status=live |archive-url=https://web.archive.org/web/20090122211743/http://talkorigins.org/faqs/faq-speciation.html |archive-date=22 January 2009 |ref=none}} * {{cite journal |last1=Weinberg |first1=James R. |last2=Starczak |first2=Victoria R. |last3=Jörg |first3=Daniele |date=August 1992 |title=Evidence for Rapid Speciation Following a Founder Event in the Laboratory |url=https://archive.org/details/sim_evolution_1992-08_46_4/page/1214 |journal=Evolution |volume=46 |issue=4 |pages=1214–1220 |doi=10.2307/2409766 |pmid=28564398 |issn=0014-3820 |jstor=2409766 |ref=none}}</ref> In sexually reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four primary geographic modes of speciation. The most common in animals is [[allopatric speciation]], which occurs in populations initially isolated geographically, such as by [[habitat fragmentation]] or migration. Selection under these conditions can produce very rapid changes in the appearance and behaviour of organisms.<ref>{{cite journal |last1=Herrel |first1=Anthony |last2=Huyghe |first2=Katleen |last3=Vanhooydonck |first3=Bieke |last4=Backeljau |first4=Thierry |last5=Breugelmans |first5=Karin |last6=Grbac |first6=Irena |last7=Van Damme |first7=Raoul |last8=Irschick |first8=Duncan J. |date=25 March 2008 |title=Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource |journal=PNAS |volume=105 |issue=12 |pages=4792–4795 |bibcode=2008PNAS..105.4792H |doi=10.1073/pnas.0711998105 |issn=0027-8424 |pmc=2290806 |pmid=18344323 |display-authors=3|doi-access=free }}</ref><ref name="Losos1997">{{cite journal |last1=Losos |first1=Jonathan B. |last2=Warhelt |first2=Kenneth I. |last3=Schoener |first3=Thomas W. |date=1 May 1997 |title=Adaptive differentiation following experimental island colonization in ''Anolis'' lizards |url=https://archive.org/details/sim_nature-uk_1997-05-01_387_6628/page/70 |journal=Nature |volume=387 |issue=6628 |pages=70–73 |bibcode=1997Natur.387...70L |doi=10.1038/387070a0 |s2cid=4242248 |issn=0028-0836}}</ref> As selection and drift act independently on populations isolated from the rest of their species, separation may eventually produce organisms that cannot interbreed.<ref>{{cite journal |last1=Hoskin |first1=Conrad J. |last2=Higgle |first2=Megan |last3=McDonald |first3=Keith R. |last4=Moritz |first4=Craig |date=27 October 2005 |title=Reinforcement drives rapid allopatric speciation |url=https://archive.org/details/sim_nature-uk_2005-10-27_437_7063/page/1353 |journal=Nature |pmid=16251964 |volume=437 |issue=7063 |pages=1353–1356 |bibcode=2005Natur.437.1353H |doi=10.1038/nature04004 |s2cid=4417281}}</ref> The second mode of speciation is [[peripatric speciation]], which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the [[founder effect]] causes rapid speciation after an increase in [[inbreeding]] increases selection on homozygotes, leading to rapid genetic change.<ref>{{cite journal |last=Templeton |first=Alan R. |author-link=Alan Templeton |date=April 1980 |title=The Theory of Speciation ''VIA'' the Founder Principle |url=http://www.genetics.org/content/94/4/1011.full.pdf+html |journal=Genetics |volume=94 |issue=4 |pages=1011–1038 |doi=10.1093/genetics/94.4.1011 |pmid=6777243 |pmc=1214177 |access-date=29 December 2014 |url-status=live |archive-url=https://web.archive.org/web/20140823063455/http://www.genetics.org/content/94/4/1011.full.pdf+html |archive-date=23 August 2014}}</ref> The third mode is [[parapatric speciation]]. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.<ref name="Gavrilets" /> Generally this occurs when there has been a drastic change in the environment within the parental species' habitat. One example is the grass ''[[Anthoxanthum|Anthoxanthum odoratum]]'', which can undergo parapatric speciation in response to localised metal pollution from mines.<ref>{{cite journal |last=Antonovics |first=Janis |s2cid=12291411 |author-link=Janis Antonovics |date=July 2006 |title=Evolution in closely adjacent plant populations X: long-term persistence of prereproductive isolation at a mine boundary |journal=[[Heredity (journal)|Heredity]] |volume=97 |issue=1 |pages=33–37 |doi=10.1038/sj.hdy.6800835 |issn=0018-067X |pmid=16639420}}</ref> Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produced a gradual change in the flowering time of the metal-resistant plants, which eventually produced complete reproductive isolation. Selection against hybrids between the two populations may cause [[Reinforcement (speciation)|reinforcement]], which is the evolution of traits that promote mating within a species, as well as [[character displacement]], which is when two species become more distinct in appearance.<ref>{{cite journal |last1=Nosil |first1=Patrik |last2=Crespi |first2=Bernard J. |last3=Gries |first3=Regine |last4=Gries |first4=Gerhard |date=March 2007 |title=Natural selection and divergence in mate preference during speciation |url=https://archive.org/details/sim_genetica_2007-03_129_3/page/309 |journal=Genetica |volume=129 |issue=3 |pages=309–327 |doi=10.1007/s10709-006-0013-6 |pmid=16900317 |s2cid=10808041 |issn=0016-6707}}</ref> [[File:Darwin's finches.jpeg|frame|[[Geographical isolation]] of [[Darwin's finches|finches]] on the [[Galápagos Islands]] produced over a dozen new species.]] Finally, in [[sympatric speciation]] species diverge without geographic isolation or changes in habitat. This form is rare since even a small amount of gene flow may remove genetic differences between parts of a population.<ref>{{cite journal |author1-link=Vincent Savolainen |last1=Savolainen |first1=Vincent |last2=Anstett |first2=Marie-Charlotte |last3=Lexer |first3=Christian |last4=Hutton |first4=Ian |last5=Clarkson |first5=James J. |last6=Norup |first6=Maria V. |last7=Powell |first7=Martyn P. |last8=Springate |first8=David |last9=Salamin |first9=Nicolas |last10=Baker |first10=William J. |date=11 May 2006 |title=Sympatric speciation in palms on an oceanic island |url=https://archive.org/details/sim_nature-uk_2006-05-11_441_7090/page/210 |journal=Nature |volume=441 |issue=7090 |pages=210–213 |bibcode=2006Natur.441..210S |doi=10.1038/nature04566 |issn=0028-0836 |pmid=16467788 |s2cid=867216 |display-authors=3 }} * {{cite journal |last1=Barluenga |first1=Marta |last2=Stölting |first2=Kai N. |last3=Salzburger |first3=Walter |last4=Muschick |first4=Moritz |last5=Meyer |first5=Axel |s2cid=3165729 |author-link5=Axel Meyer |date=9 February 2006 |title=Sympatric speciation in Nicaraguan crater lake cichlid fish |journal=Nature |volume=439 |issue=7077 |pages=719–23 |bibcode=2006Natur.439..719B |doi=10.1038/nature04325 |issn=0028-0836 |pmid=16467837 |display-authors=3 |url=http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-34004 |ref=none |access-date=30 July 2022 |archive-date=30 July 2022 |archive-url=https://web.archive.org/web/20220730090843/http://kops.uni-konstanz.de/handle/123456789/6577 |url-status=live }}</ref> Generally, sympatric speciation in animals requires the evolution of both [[Polymorphism (biology)|genetic differences]] and nonrandom mating, to allow reproductive isolation to evolve.<ref>{{cite journal |last=Gavrilets |first=Sergey |date=21 March 2006 |title=The Maynard Smith model of sympatric speciation |journal=Journal of Theoretical Biology |volume=239 |issue=2 |pages=172–182 |doi=10.1016/j.jtbi.2005.08.041 |issn=0022-5193 |pmid=16242727|bibcode=2006JThBi.239..172G }}</ref> One type of sympatric speciation involves [[crossbreed]]ing of two related species to produce a new hybrid species. This is not common in animals as animal hybrids are usually sterile. This is because during [[meiosis]] the [[homologous chromosome]]s from each parent are from different species and cannot successfully pair. However, it is more common in plants because plants often double their number of chromosomes, to form [[polyploidy|polyploids]].<ref>{{cite journal |last1=Wood |first1=Troy E. |last2=Takebayashi |first2=Naoki |last3=Barker |first3=Michael S. |last4=Mayrose |first4=Itay |last5=Greenspoon |first5=Philip B. |last6=Rieseberg |first6=Loren H. |date=18 August 2009 |title=The frequency of polyploid speciation in vascular plants |journal=PNAS |volume=106 |issue=33 |pages=13875–13879 |bibcode=2009PNAS..10613875W |doi=10.1073/pnas.0811575106 |issn=0027-8424 |pmc=2728988 |pmid=19667210 |display-authors=3|doi-access=free }}</ref> This allows the chromosomes from each parental species to form matching pairs during meiosis, since each parent's chromosomes are represented by a pair already.<ref>{{cite journal |last1=Hegarty |first1=Matthew J. |last2=Hiscock |first2=Simon J. |s2cid=1584282 |date=20 May 2008 |title=Genomic Clues to the Evolutionary Success of Polyploid Plants |journal=Current Biology |volume=18 |issue=10 |pages=R435–R444 |doi=10.1016/j.cub.2008.03.043 |issn=0960-9822 |pmid=18492478|doi-access=free |bibcode=2008CBio...18.R435H }}</ref> An example of such a speciation event is when the plant species ''[[Arabidopsis thaliana]]'' and ''[[Arabidopsis arenosa]]'' crossbred to give the new species ''Arabidopsis suecica''.<ref>{{cite journal |last1=Jakobsson |first1=Mattias |last2=Hagenblad |first2=Jenny |last3=Tavaré |first3=Simon |author-link3=Simon Tavaré |last4=Säll |first4=Torbjörn |last5=Halldén |first5=Christer |last6=Lind-Halldén |first6=Christina |last7=Nordborg |first7=Magnus |date=June 2006 |title=A Unique Recent Origin of the Allotetraploid Species ''Arabidopsis suecica'': Evidence from Nuclear DNA Markers |journal=Molecular Biology and Evolution |volume=23 |issue=6 |pages=1217–1231 |doi=10.1093/molbev/msk006 |pmid=16549398 |display-authors=3 |url=http://hkr.diva-portal.org/smash/get/diva2:424478/FULLTEXT01 |doi-access=free |access-date=30 July 2022 |archive-date=15 February 2022 |archive-url=https://web.archive.org/web/20220215191506/http://hkr.diva-portal.org/smash/get/diva2:424478/FULLTEXT01 |url-status=live }}</ref> This happened about 20,000 years ago,<ref>{{cite journal |last1=Säll |first1=Torbjörn |last2=Jakobsson |first2=Mattias |last3=Lind-Halldén |first3=Christina |last4=Halldén |first4=Christer |date=September 2003 |title=Chloroplast DNA indicates a single origin of the allotetraploid ''Arabidopsis suecica'' |journal=Journal of Evolutionary Biology |volume=16 |issue=5 |pages=1019–1029 |doi=10.1046/j.1420-9101.2003.00554.x |pmid=14635917|s2cid=29281998 |doi-access=free }}</ref> and the speciation process has been repeated in the laboratory, which allows the study of the genetic mechanisms involved in this process.<ref>{{cite journal |last1=Bomblies |first1=Kirsten |author-link1=Kirsten Bomblies |last2=Weigel |first2=Detlef |author-link2=Detlef Weigel |date=December 2007 |title=''Arabidopsis''—a model genus for speciation |journal=Current Opinion in Genetics & Development |volume=17 |issue=6 |pages=500–504 |doi=10.1016/j.gde.2007.09.006 |pmid=18006296}}</ref> Indeed, chromosome doubling within a species may be a common cause of reproductive isolation, as half the doubled chromosomes will be unmatched when breeding with undoubled organisms.<ref name="Semon">{{cite journal |last1=Sémon |first1=Marie |last2=Wolfe |first2=Kenneth H. |date=December 2007 |title=Consequences of genome duplication |journal=Current Opinion in Genetics & Development |volume=17 |issue=6 |pages=505–512 |doi=10.1016/j.gde.2007.09.007 |pmid=18006297}}</ref> Speciation events are important in the theory of [[punctuated equilibrium]], which accounts for the pattern in the fossil record of short "bursts" of evolution interspersed with relatively long periods of stasis, where species remain relatively unchanged.<ref>{{harvnb|Eldredge|Gould|1972|pp=82–115}}</ref> In this theory, speciation and [[Contemporary evolution|rapid evolution]] are linked, with natural selection and genetic drift acting most strongly on organisms undergoing speciation in novel habitats or small populations. As a result, the periods of stasis in the fossil record correspond to the parental population and the organisms undergoing speciation and rapid evolution are found in small populations or geographically restricted habitats and therefore rarely being preserved as fossils.<ref name="Gould_1994" /> Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here. You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Christianpedia:Copyrights for details). Do not submit copyrighted work without permission! Cancel Editing help (opens in new window) Discuss this page