Population bottleneck and recovery or extinction

A population bottleneck (or genetic bottleneck) is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing, and the population is reduced by 50% or more, often by several orders of magnitude. eVolution is the third Album by eLDee, it was due to be released in 2008 An order of magnitude is the class of scale or magnitude of any amount where each class contains values of a fixed ratio to the class preceding it ^[1]

Population bottlenecks increase genetic drift, as the rate of drift is inversely proportional to the population size. In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time They also increase inbreeding due to the reduced pool of possible mates (see small population size). Inbreeding is breeding between close Relatives whether plant or animal Populations with small population size behave differently to larger populations

A slightly different sort of genetic bottleneck can occur if a small group becomes reproductively separated from the main population. This is called a founder effect. In Population genetics, the founder effect refers to the loss of genetic variation when a new colony is established by a very small number of individuals from a larger

Examples

Humans

Human mitochondrial DNA (inherited only from one's mother) and Y chromosome DNA (from one's father) show coalescence at around 140,000 and 60,000 years ago respectively. Mitochondrial DNA ( mtDNA) is the DNA located in Organelles called mitochondria. The Y chromosome is the sex-determining Chromosome in most Mammals including Humans In mammals it contains the gene SRY, which triggers In Genetics, coalescent theory is a retrospective model of population genetics that traces all Alleles of a Gene in a sample from a population to a single In other words, all living humans' female line ancestry trace back to a single female (Mitochondrial Eve) at around 140,000 years ago. Matrilineality is a system in which lineage is traced through the mother and maternal ancestors Mitochondrial Eve ( mt-mrca) is the name given by researchers to the woman who is defined as the Matrilineal most recent common ancestor (MRCA for all currently Via the male line, all humans can trace their ancestry back to a single male (Y-chromosomal Adam) at around 60,000 years ago. Patrilineality (aka agnatic kinship) is a system in which one belongs to one's father's lineage it generally involves the Inheritance of property names or titles In human Genetics, Y-chromosomal Adam ( Y- MRCA) is the patrilineal Human Most recent common ancestor (MRCA from whom all ^[2]

However, such coalescence is genetically expected and does not, in itself, indicate a population bottleneck, because mitochondrial DNA and Y-chromosome are only a small part of the entire genome, and are atypical in that they are inherited exclusively through the mother or through the father, respectively. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby Most genes in the genome are inherited from either father or mother, thus can be traced back in time via either matrilinear or patrilinear ancestry. ^[3] Research on many (but not necessarily most) genes find different coalescence points from 2 million years ago to 60,000 years ago when different genes are considered, thus disproving the existence of more recent extreme bottlenecks (i. e. a single breeding pair). ^[4][5]

But this is not inconsistent with the Toba catastrophe theory which suggests that a bottleneck of the human population occurred ca. According to the Toba catastrophe theory, 70000 to 75000 years ago a supervolcanic event at Lake Toba, on Sumatra, reduced the world's human population 70,000 years ago, proposing that the human population was reduced to a c. 15,000 individuals^[5] when the Toba supervolcano in Indonesia erupted and triggered a major environmental change. Lake Toba ( Danau Toba) is a Lake and Supervolcano, 100 km long and 30 km wide and 505 m A supervolcano or super volcanic eruption is a Volcanic eruption which is Orders of magnitude greater than any volcano in historic times (generally accepted to be The Republic of Indonesia ( (Republik Indonesia is a Country in Southeast Asia. See also Nature The natural environment, commonly referred to simply as the environment, is a terminology that is comprised of all living and The theory is based on geological evidences of sudden climate change, and on coalescence evidences of some genes (including mitochondrial DNA, Y-chromosome and some nuclear genes)^[6] and the relatively low level of genetic variation with humans. ^[5]

On the other hand, 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. 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. ^[7] 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^[8]

Animals

Wisent, also called European bison, faced extinction in the early 20th century. The Upper Paleolithic (or Upper Palaeolithic) is the third and last subdivision of the Paleolithic or Old Stone Age as it is understood in Europe Africa Year 1890 ( MDCCCXC) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. The wisent (ˈviːzənt or European bison ( Bison bonasus) is a Bison Species and the heaviest surviving land animal in Europe The twentieth century of the Common Era began on 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 (Luenser et al. , 2005). The population of American Bison fell due to overhunting, nearly leading to extinction around the year 1890 and has since begun to recover (see table). The American bison ( Bison bison) is a Bovine Mammal, also commonly known as the American buffalo.

A classic example of a population bottleneck is that of the Northern Elephant Seals, whose population fell to about 30 in the 1890s although it now numbers in the hundreds of thousands. The Northern Elephant Seal ( Mirounga angustirostris) is one of two Species of Elephant seal (the other is the Southern Elephant Seal) Another example are Cheetahs, which are so closely related to each other that skin grafts from one cheetah to another do not provoke immune responses, thus suggesting an extreme population bottleneck in the past. The cheetah ( Acinonyx jubatus) is an atypical member of the cat family ( Felidae) that is unique in its speed while lacking climbing abilities Skin grafting is a type of Medical grafting involving the transplantation of Skin. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Another largely bottlenecked species is the Golden Hamster, of which the vast majority are descended from a single litter found in the Syrian desert around 1930. The Syrian or Golden Hamster, Mesocricetus auratus, is a very well-known member of the Rodent Subfamily Cricetinae, the Syria ( سوريّة or) officially the Syrian Arab Republic (Arabic ar الجمهورية العربية السورية Year 1930 ( MCMXXX) was a Common year starting on Wednesday (link will display 1930 calendar of the Gregorian calendar.

Saiga Antelope numbers have plummeted more than 95% from about 1 million in 1990 to less than 30,000 in 2004, mainly due to poaching for traditional Chinese medicine. ^[9]

According to a paper published in 2002, the genome of the Giant Panda shows evidence of a severe bottleneck that took place about 43,000 years ago. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby The Giant Panda ( Ailuropoda melanoleuca, "black-and-white cat-foot" is a Mammal classified in the Bear family ( Ursidae) native to ^[10] There is also evidence of at least one primate species that suffered from a bottleneck around this time scale.

Sometimes further deductions can 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 Alcedo volcano is significantly less diverse than four other tortoise populations on the same island. Researchers' DNA analysis dates the bottleneck around 88,000 years before present (YBP), according to a notice in Science, October 3, 2003. Before Present (BP years are a time scale used in Archaeology, Geology, and other scientific disciplines to specify when events in the past occurred Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. About 100,000 YBP the volcano erupted violently, burying much of the tortoise habitat deep in pumice and ash.

Plants

Research showed that there is no genetic variability in the genome of the Wollemi Pine (Wollemia nobilis), indicating that the species (of which there are only around 100 specimens in the wild and tens of thousands cultivated) went through a severe population bottleneck.

Population bottlenecks in evolutionary theory

As a population becomes smaller, genetic drift plays a bigger role in speciation. In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time Speciation is the Evolutionary process by which new biological Species arise A land animal like a brown bear might find itself locally reduced to a few dozen pairs on an Arctic island. The Brown Bear ( Ursus arctos) is an Omnivorous Mammal of the family Ursidae, distributed across much of northern Eurasia and That likely happened as the last Ice Age came to an end, and the Bering land bridge receded into the sea. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets The Bering land bridge was a Land bridge roughly 1000 miles (1600 km north to south at its greatest extent which joined present-day Alaska and eastern Siberia In that circumstance, a beneficial trait appearing in an alpha male or two may change the color, size, swimming ability, cold resistance, or aggressiveness of the group in just a few generations. In Social animals the alpha male is the individual in the community to whom the others follow and defer Generation (from the Greek γενεά) also known as procreation, is the act of producing Offspring. This would be an example of punctuated equilibrium. Punctuated equilibrium is a theory of evolutionary biology which states that most sexually reproducing populations experience little change for most of their geological

Minimum viable population size

In conservation biology, minimum viable population size (MVP) helps to determine the effective population size when a population is at risk for extinction (Gilpin and Soulé, 1986 and Soulé, 1987). "Conservation Biology" redirects here For the Scientific journal, see Conservation Biology (journal. Minimum viable population (MVP is a lower bound on the population of a species such that it can survive in the wild In Population genetics, the concept of effective population size N e was introduced by the American Geneticist Sewall In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. There is considerable debate about the value of the MVP.

Population bottleneck in fiction

Kurt Vonnegut's 1985 novel Galápagos involves a human population bottleneck which causes drastic evolutionary changes. Kurt Vonnegut Jr (November 11 1922 – April 11 2007 (ˈvɒnəgət was a prolific and genre-bending American Novelist known for works blending Satire, Black The novel Galápagos is Kurt Vonnegut 's look at evolution It was first published in 1985 by Delacorte.

See also

• Small population size
• Effective population size
• Founder effect
• Overpopulation
• Ice age
• Black Death

References

External links

• ScienceDaily: Big Bang Theory Of Human Evolution?
• Northern Elephant Seal History