population bottleneck

{{Main|Minimum viable population}}

In conservation biology, minimum viable population (MVP) size helps to determine the effective population size when a population is at risk for extinction.{{cite book |last1=Gilpin |first1=M.E. |last2=Soulé |first2=M.E. |year=1986 |chapter=Minimum viable populations: The processes of species extinctions |editor1-first=Michael E. |editor1-last=Soulé |title=Conservation biology: The science of scarcity and diversity |pages=13–34 |location=Sunderland Mass |publisher=Sinauer Associates |isbn=978-0-87893-794-3}}{{cite book |editor1-last=Soulé |editor1-first=Michael E. |year=1987 |title=Viable populations for conservation |url=https://archive.org/details/isbn_9780521336574 |url-access=registration |location=Cambridge |publisher=Cambridge Univ. Press |isbn=978-0-521-33657-4}}{{page needed|date=March 2014}} The effects of a population bottleneck often depend on the number of individuals remaining after the bottleneck and how that compares to the minimum viable population size.

{{main|Founder effect}}

A slightly different form of bottleneck can occur if a small group becomes reproductively (e.g., geographically) separated from the main population, such as through a founder event, e.g., if a few members of a species successfully colonize a new isolated island, or from small captive breeding programs such as animals at a zoo. Alternatively, invasive species can undergo population bottlenecks through founder events when introduced into their invaded range.Lee, C. E. (2002). Evolutionary genetics of invasive species. Trends in ecology & evolution, 17(8), 386-391.

{{See also|Founder effect#Among human populations}}

According to a 1999 model, a severe population bottleneck, or more specifically a full-fledged speciation, occurred among a group of Australopithecina as they transitioned into the species known as Homo erectus two million years ago. It is believed that additional bottlenecks must have occurred since Homo erectus started walking the Earth, but current archaeological, paleontological, and genetic data are inadequate to give much reliable information about such conjectured bottlenecks.{{cite journal |vauthors=Hawks J, Hunley K, Lee SH, Wolpoff M |title=Population bottlenecks and Pleistocene human evolution |journal=Molecular Biology and Evolution |volume=17 |issue=1 |pages=2–22 |date=January 2000 |pmid=10666702 |doi=10.1093/oxfordjournals.molbev.a026233|doi-access=free }} Nonetheless, a 2023 genetic analysis discerned such a human ancestor population bottleneck of a possible 100,000 to 1000 individuals "around 930,000 and 813,000 years ago [which] lasted for about 117,000 years and brought human ancestors close to extinction."{{cite news |last=Zimmer |first=Carl |authorlink=Carl Zimmer |title=Humanity's Ancestors Nearly Died Out, Genetic Study Suggests - The population crashed following climate change about 930,000 years ago, scientists concluded. Other experts aren't convinced by the analysis. |url=https://www.nytimes.com/2023/08/31/science/human-survival-bottleneck.html |date=31 August 2023 |work=the New York Times |url-status=live |archiveurl= https://archive.today/20230831182259/https://www.nytimes.com/2023/08/31/science/human-survival-bottleneck.html |archivedate=31 August 2023 |accessdate=2 September 2023 }}{{cite journal |author=Hu, Wangjie |display-authors=et al. |title=Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition |url=http://www.science.org/doi/10.1126/science.abq7487 |date=31 August 2023 |journal=Science |volume=381 |issue=6661 |pages=979–984 |doi=10.1126/science.abq7487 |pmid=37651513 |bibcode=2023Sci...381..979H |s2cid=261396309 |url-status=live |archiveurl=https://archive.today/20230901024052/https://www.science.org/doi/10.1126/science.abq7487 |archivedate=1 September 2023 |accessdate=2 September 2023 }}

The controversial Toba catastrophe theory, presented in the late 1990s to early 2000s, suggested that a supervolcano eruption in Indonesia approximately 75,000 years ago caused a human population bottleneck to 10,000–30,000 individuals.{{cite book

|first=Richard |last=Dawkins |author-link=Richard Dawkins |title=The Ancestor's Tale, A Pilgrimage to the Dawn of Life |chapter=The Grasshopper's Tale |page=416 |publisher=Houghton Mifflin Company |location=Boston |year=2004 |isbn=0-297-82503-8|title-link=The Ancestor's Tale }} The hypothesis was based on the apparent coincidence of geological evidence of sudden climate change, coalescence evidence of some genes.{{cite journal |author=Ambrose SH |title=Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans |journal=Journal of Human Evolution |volume=34 |issue=6 |pages=623–51 |date=June 1998 |pmid=9650103 |doi=10.1006/jhev.1998.0219|bibcode=1998JHumE..34..623A |s2cid=33122717 }} and the relatively low level of genetic variation in humans. However, subsequent research, especially in the 2010s, appeared to refute both the genetic argument and the extent of climate change at the time.{{cite news|url=http://phys.org/news/2013-05-volcanic-winter-toba-super-eruption.html |title=Doubt over 'volcanic winter' after Toba super-eruption. 2013 |work=Phys.org |date=2013-05-02 |access-date=2015-10-31}}

In 2000, a Molecular Biology and Evolution paper suggested a transplanting model or a 'long bottleneck' to account for the limited genetic variation, rather than a catastrophic environmental change. This would be consistent with suggestions that in sub-Saharan Africa numbers could have dropped at times as low as 2,000, for perhaps as long as 100,000 years, before numbers began to expand again in the Late Stone Age.{{cite journal |vauthors=Behar DM, Villems R, Soodyall H, etal |title=The dawn of human matrilineal diversity |journal=American Journal of Human Genetics |volume=82 |issue=5 |pages=1130–40 |date=May 2008 |pmid=18439549 |pmc=2427203 |doi=10.1016/j.ajhg.2008.04.002}}

• {{cite news |author=Paul Rincon |date=April 24, 2008 |title=Human line 'nearly split in two' |work=BBC News |url=http://news.bbc.co.uk/2/hi/science/nature/7358868.stm}}

The Neolithic Y-chromosome bottleneck refers to a period around 5000 BC where the diversity in the male y-chromosome dropped precipitously, to a level equivalent to reproduction occurring with a ratio between men and women of 1:17.{{cite news | access-date=12 September 2023 | first1=Michelle | last1=Starr | url=https://www.sciencealert.com/neolithic-y-chromosome-bottleneck-warring-patrilineal-clans | title=Something Weird Happened to Men 7,000 Years Ago, And We Finally Know Why | publisher=sciencealert.com | date=31 May 2018}} Discovered in 2015, the research suggests that the reason for the bottleneck may not be a reduction in the number of males, but a drastic decrease in the percentage of males with reproductive success.{{cite journal |author=Karmin |display-authors=et al. |year=2015 |title=A recent bottleneck of Y chromosome diversity coincides with a global change in culture |journal=Genome Research |volume=25 |issue=4 |pages=459–466 |doi=10.1101/gr.186684.114 |pmc=4381518 |pmid=25770088 |doi-access=free}}

European bison, also called wisent (Bison bonasus), faced extinction in the early 20th century. The animals living today are all descended from 12 individuals and they have extremely low genetic variation, which may be beginning to affect the reproductive ability of bulls.{{cite journal |doi=10.1007/s10344-005-0081-4 |title=Low level of genetic variability in European bisons (Bison bonasus) from the Bialowieza National Park in Poland |journal=European Journal of Wildlife Research |volume=51 |issue=2 |pages=84–7 |year=2005 |last1=Luenser |first1=K. |last2=Fickel |first2=J. |last3=Lehnen |first3=A. |last4=Speck |first4=S. |last5=Ludwig |first5=A.|bibcode=2005EJWR...51...84L |s2cid=34102378 }}

The population of American bison (Bison bison) fell due to overhunting, nearly leading to extinction around the year 1890, though it has since begun to recover (see table).

Image:Northern Elephant Seal, San Simeon2.jpg to the brink of extinction by the late 19th century. Although they have made a comeback, the genetic variation within the population remains very low.]]

A classic example of a population bottleneck is that of the northern elephant seal, whose population fell to about 30 in the 1890s. Although it now numbers in the hundreds of thousands, the potential for bottlenecks within colonies remains. Dominant bulls are able to mate with the largest number of females—sometimes as many as 100. With so much of a colony's offspring descended from just one dominant male, genetic diversity is limited, making the species more vulnerable to diseases and genetic mutations.

The golden hamster is a similarly bottlenecked species, with the vast majority of domesticated hamsters descended from a single litter found in the Syrian desert around 1930, and very few wild golden hamsters remain.

An extreme example of a population bottleneck is the New Zealand black robin, of which every specimen today is a descendant of a single female, called Old Blue. The Black Robin population is still recovering from its low point of only five individuals in 1980.

The genome of the giant panda shows evidence of a severe bottleneck about 43,000 years ago.{{cite journal |doi=10.1351/pac200274040575 |title=Genetic diversity and conservation of endangered animal species |journal=Pure and Applied Chemistry |volume=74 |issue=4 |pages=575–84 |year=2002 |last1=Zhang |first1=Ya-Ping |last2=Wang |first2=Xiao-xia |last3=Ryder |first3=Oliver A. |last4=Li |first4=Hai-Peng |last5=Zhang |first5=He-Ming |last6=Yong |first6=Yange |last7=Wang |first7=Peng-yan|s2cid=13945117 |url=http://www.degruyter.com/downloadpdf/j/pac.2002.74.issue-4/pac200274040575/pac200274040575.xml |doi-access=free }} There is also evidence of at least one primate species, the golden snub-nosed monkey, that also suffered from a bottleneck around this time. An unknown environmental event is suspected to have caused the bottlenecks observed in both of these species. The bottlenecks likely caused the low genetic diversity observed in both species.

Other facts can sometimes be inferred from an observed population bottleneck. Among the Galápagos Islands giant tortoises—themselves a prime example of a bottleneck—the comparatively large population on the slopes of the Alcedo volcano is significantly less diverse than four other tortoise populations on the same island. DNA analyses date the bottleneck to around 88,000 years before present (YBP).{{cite journal |vauthors=Beheregaray LB, Ciofi C, Geist D, Gibbs JP, Caccone A, Powell JR |title=Genes record a prehistoric volcano eruption in the Galápagos |journal=Science |volume=302 |issue=5642 |pages=75 |date=October 2003 |pmid=14526072 |doi=10.1126/science.1087486|s2cid=39102858 }} About 100,000 YBP the volcano erupted violently, deeply burying much of the tortoise habitat in pumice and ash.

Another example can be seen in the greater prairie chickens, which were prevalent in North America until the 20th century. In Illinois alone, the number of greater prairie chickens plummeted from over 100 million in 1900 to about 46 in 1998.{{Cite journal |last1=Mussmann |first1=S. M. |last2=Douglas |first2=M. R. |last3=Anthonysamy |first3=W. J. B. |last4=Davis |first4=M. A. |last5=Simpson |first5=S. A. |last6=Louis |first6=W. |last7=Douglas |first7=M. E. |date=February 2017 |title=Genetic rescue, the greater prairie chicken and the problem of conservation reliance in the Anthropocene |journal=Royal Society Open Science |language=en |volume=4 |issue=2 |pages=160736 |doi=10.1098/rsos.160736 |issn=2054-5703 |pmc=5367285 |pmid=28386428|bibcode=2017RSOS....460736M }} These declines in population were the result of hunting and habitat destruction, but the random consequences have also caused a great loss in species diversity. DNA analysis comparing the birds from 1990 and mid-century shows a steep genetic decline in recent decades. Management of the greater prairie chickens now includes genetic rescue efforts including translocation of prairie chickens between leks to increase each population's genetic diversity.

Population bottlenecking poses a major threat to the stability of species populations as well. Papilio homerus is the largest butterfly in the Americas and is endangered according to the IUCN. The disappearance of a central population poses a major threat of population bottleneck. The remaining two populations are now geographically isolated and the populations face an unstable future with limited remaining opportunity for gene flow.{{Cite journal|last1=Lehnert|first1=Matthew S.|last2=Kramer|first2=Valerie R.|last3=Rawlins|first3=John E.|last4=Verdecia|first4=Vanessa|last5=Daniels|first5=Jaret C.|date=2017-07-10|title=Jamaica's Critically Endangered Butterfly: A Review of the Biology and Conservation Status of the Homerus Swallowtail (Papilio (Pterourus) homerus Fabricius)|journal=Insects|language=en|volume=8|issue=3|pages=68|doi=10.3390/insects8030068|pmid=28698508|pmc=5620688|doi-access=free}}

Genetic bottlenecks exist in cheetahs.{{cite journal | pmc=46261 | pmid=8475057 | volume=90 |issue = 8| title=Dating the genetic bottleneck of the African cheetah. | date=Apr 1993 | journal=Proc Natl Acad Sci U S A | pages=3172–6 | doi=10.1073/pnas.90.8.3172|last1 = Menotti-Raymond|first1 = M.|last2 = O'Brien|first2 = S. J.| bibcode=1993PNAS...90.3172M | doi-access=free }}{{cite journal|last1=O'Brien|first1=S.|last2=Roelke|first2=M.|last3=Marker|first3=L|last4=Newman|first4=A|last5=Winkler|first5=C.|last6=Meltzer|first6=D|last7=Colly|first7=L|last8=Evermann|first8=J.|last9=Bush|first9=M|last10=Wildt|first10=D.|title=Genetic basis for species vulnerability in the cheetah|journal=Science|volume=227|issue=4693|date=March 22, 1985|pages=1428–1434|doi=10.1126/science.2983425|pmid=2983425|bibcode=1985Sci...227.1428O|url=http://bio150.chass.utoronto.ca/labs/cool-links/lab5/OBrien_et_al_1985_lab_5.pdf|archive-url=https://web.archive.org/web/20060507232241/http://bio150.chass.utoronto.ca/labs/cool-links/lab5/OBrien_et_al_1985_lab_5.pdf|archive-date=2006-05-07}}

Bottlenecks also exist among pure-bred animals (e.g., dogs and cats: pugs, Persian) because breeders limit their gene pools to a few (show-winning) individuals for their looks and behaviors. The extensive use of desirable individual animals at the exclusion of others can result in a popular sire effect.

Selective breeding for dog breeds caused constricting breed-specific bottlenecks.{{cite journal |last1=Lindblad-Toh |first1=K. |last2=Wade |first2=C. M. |last3=Mikkelsen |first3=T. S. |last4=Karlsson |first4=E. K. |year=2005 |title=Genome sequence, comparative analysis and haplotype structure of the domestic dog |journal=Nature |volume=438 |issue=7069 |pages=803–819 |doi=10.1038/nature04338 |pmid=16341006 |bibcode=2005Natur.438..803L |doi-access=free }} These bottlenecks have led to dogs having an average of 2–3% more genetic loading than gray wolves.{{cite journal |last1=Marsden |first1=C. D. |last2=Ortega-Del Vecchyo |first2=D. |last3=O'Brien |first3=D. P. |last4=Taylor |first4=J. F. |last5=Ramirez |first5=O. |last6=Vilà |first6=C. |last7=Marques-Bonet |first7=T. |last8=Schnabel |first8=R. D. |last9=Wayne |first9=R. K. |last10=Lohmueller |first10=K. E. |display-authors=3 |year=2016 |title=Bottlenecks and selective sweeps during domestication have increased deleterious genetic variation in dogs |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=1 |pages=152–157 |doi=10.1073/pnas.1512501113 |pmid=26699508 |pmc=4711855 |bibcode=2016PNAS..113..152M |doi-access=free }} The strict breeding programs and population bottlenecks have led to the prevalence of diseases such as heart disease, blindness, cancers, hip dysplasia, and cataracts.

Selective breeding to produce high-yielding crops has caused genetic bottlenecks in these crops and has led to genetic homogeneity.National Research Council. (1972). Genetic vulnerability of major crops. National Academies. This reduced genetic diversity in many crops could lead to broader susceptibility to new diseases or pests, which threatens global food security.{{cite journal |last1=Hyten |first1=D. L. |last2=Song |first2=Q. |last3=Zhu |first3=Y. |last4=Choi |first4=I. Y. |last5=Nelson |first5=R. L. |last6=Costa |first6=J. M. |display-authors=3 |last7=Cregan |first7=P. B. |year=2006 |title=Impacts of genetic bottlenecks on soybean genome diversity |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=45 |pages=16666–16671 |doi=10.1073/pnas.0604379103 |pmid=17068128 |pmc=1624862 |bibcode=2006PNAS..10316666H |doi-access=free }}

Research showed that there is incredibly low, nearly undetectable amounts of genetic diversity in the genome of the Wollemi pine (Wollemia nobilis).{{cite journal |last1=Peakall |first1=R. |last2=Ebert |first2=D. |last3=Scott |first3=L. J. |last4=Meagher |first4=P. F. |last5=Offord |first5=C. A. |year=2003 |title=Comparative genetic study confirms exceptionally low genetic variation in the ancient and endangered relictual conifer, Wollemia nobilis (Araucariaceae) |journal=Molecular Ecology |volume=12 |issue=9 |pages=2331–2343 |doi=10.1046/j.1365-294X.2003.01926.x |pmid=12919472 |bibcode=2003MolEc..12.2331P |s2cid=35255532 }} The IUCN found a population count of 80 mature individuals and about 300 seedlings and juveniles in 2011, and previously, the Wollemi pine had fewer than 50 individuals in the wild.{{cite journal |doi=10.2305/IUCN.UK.2011-2.RLTS.T34926A9898196.en |title=Wollemia nobilis |last=Thomas |first=P. |journal=The IUCN Red List of Threatened Species |year=2011|doi-access=free }} The low population size and low genetic diversity indicates that the Wollemi pine went through a severe population bottleneck.

A population bottleneck was created in the 1970s through the conservation efforts of the endangered Mauna Kea silversword (Argyroxiphium sandwicense ssp. sandwicense).{{cite journal |last1=Robichaux |first1=R. H. |last2=Friar |first2=E. A. |last3=Mount |first3=D. W. |year=1997 |title=Molecular Genetic Consequences of a Population Bottleneck Associated with Reintroduction of the Mauna Kea Silversword (Argyroxiphium sandwicense ssp. sandwicense [Asteraceae]) |journal=Conservation Biology |volume=11 |issue=5 |pages=1140–1146 |doi=10.1046/j.1523-1739.1997.96314.x |s2cid=83819334 }} The small natural population of silversword was augmented through the 1970s with outplanted individuals. All of the outplanted silversword plants were found to be first or subsequent generation offspring of just two maternal founders. The low amount of polymorphic loci in the outplanted individuals led to the population bottleneck, causing the loss of the marker allele at eight of the loci.

• Baby boom
• Population boom

{{Reflist|30em}}

{{Commons category|Population bottleneck}}

• {{cite journal |vauthors=Hawks J, Hunley K, Lee SH, Wolpoff M |title=Population bottlenecks and Pleistocene human evolution |journal=Molecular Biology and Evolution |volume=17 |issue=1 |pages=2–22 |date=January 2000 |pmid=10666702 |doi=10.1093/oxfordjournals.molbev.a026233|doi-access=free}}
• {{cite press release |date=January 10, 2000 |title=New study suggests big bang theory of human evolution |website=University of Michigan, Department of Anthropology |url=http://ns.umich.edu/Releases/2000/Jan00/r011000b.html |access-date=March 4, 2014 |archive-date=February 5, 2014 |archive-url=https://web.archive.org/web/20140205024640/http://www.ns.umich.edu/Releases/2000/Jan00/r011000b.html |url-status=dead }}
• [https://web.archive.org/web/20040515084856/http://essp.csumb.edu/eseal/kristi_west/history.html Northern Elephant Seal History]
• {{cite journal |author=Nei M |title=Bottlenecks, genetic polymorphism and speciation |journal=Genetics |volume=170 |issue=1 |pages=1–4 |date=May 2005 |doi=10.1093/genetics/170.1.1 |pmid=15914771 |pmc=1449701 |url=http://www.genetics.org/cgi/pmidlookup?view=long&pmid=15914771}}

{{Population genetics}}

{{DEFAULTSORT:Population Bottleneck}}

Category:Population dynamics

Category:Population genetics

Category:Human evolution