Founder population
When a species invades a new area, the original, small population is called a founder population. The new area may be as small as a recently-erupted volcanic island, or as large as North America, invaded by species across Beringia during the last Ice age.
The concept of a founder population is usually seen in a context of subsequent population growth. Such populations that have recently arisen from small founder populations will exhibit reduced genetic variation due to the population bottleneck. The genetics of Easter Islanders and those native to Pitcairn Island provide examples of such a gene pool of limited variation.
Founder populations are essential to the study of island biogeography. A natural tabula rasa is not easily found, but a classic series of studies on founder population effects were done following the catastrophic eruption in 1883 of Krakatau, ('Krakatoa'), which erased all life on the island remnant. Another ongoing study has been following the biocolonization of Surtsey, Iceland, a new volcanic island that erupted offshore between 1963 and 1967. An earlier event, the Toba eruption in Sumatra of about 73,000 ybp covered much of India with 3-6 m of ash, and must have coated the Nicobar Islands and Andaman Islands, much nearer in the ash fallout cone, with life-smothering layers, restarting their biodiversity from effectively zero [1] (http://www.andaman.org/book/app-r/ch3_explosion/textr3.htm).
An effective founder population consists only of those whose genetic print is identifiable in subsequent populations. Because in sexual reproduction, genetic recombination ensures that with each generation only half the genetic material of a parent is represented in the offspring, some genetic lines may die out entirely, even though there are numerous progeny. A recent study (Hey 2005) concluded that of the people migrating across the Bering land bridge at the close of the ice age, only 70 left their genetic print in modern descendents, a minute effective founder population— which is easily misread as though implying that only 70 people crossed to North America. The misinterpretations of "Mitochondrial Eve" are a case in point: it may be hard to explain that a "mitochondrial Eve" was not the only woman of her time.
The effective founder population of Quebec was only 2,600. After twelve to sixteen generations, with an eighty-fold growth but minimal gene dilution from intermarriage, Quebec has what geneticists call optimal linkage disequilibrium (genetic sharing) [2] (http://www.genizon.com/html/content.asp?node=14). The result: far fewer genetic variations, including those that have been well studied because they are connected with inheritable diseases.
A cultural meme may die out in a comparable way, as when a surname or title becomes extinct through lack of Y chromosomes, even though there is a flourishing population of descendants, all through female lines.
External link
- Genizon.com: (http://www.genizon.com/html/content.asp?node=14) Quebec Founder Population
References
- Hey, Jody, 2005. "On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas" in PLoS Biol 2005 May 24;3(6):e193 [3] (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15898833&query_hl=1)
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