Species Not Subject To Inbreeding Depression
Inbreeding depression is not a phenomenon that will inevitably occur. Given enough time and a sufficiently (but not too) small gene pool, deleterious alleles may be eliminated by natural selection and genetic drift.
Under most circumstances, this is a rare occurrence though, as the gene pool cannot become too large (thereby increasing the odds of new deleterious alleles appearing through mutation) nor too small (resulting in outright inbreeding depression). Among island endemic populations, however, a high resistance to inbreeding depression is often seen. These derive from very small initial populations that must have been viable, and panmixia in the early stages of speciation was usually thorough. This will result in a very comprehensive elimination of deleterious recessive alleles at least. The second type of inbreeding depression – caused by overdominant heterozygous alleles – is impossible to eliminate by panmixia. However, local conditions may result in an altered selective advantage, so that the fitness of the heterozygous genotype is lowered.
Example taxa not subject to significant inbreeding depression despite extremely low effective population sizes:
Animals
- Chatham Islands Robin
- Laysan Duck (data equivocal; severe population fluctuations probably natural)
- Mauritius Kestrel
- Naked Mole Rat (mammal displaying eusocial reproductive structure and low genetic variation)
- Stegodyphus dumicola and some other social spiders (live in highly inbred colonies)
- Thai Ridgeback, a dog breed
Plants
- Dandelion (reproduces asexually through apomixis)
- Nihoa Carnation
- Toromiro
Read more about this topic: Inbreeding Depression
Famous quotes containing the words species, subject, inbreeding and/or depression:
“The further our civilization advances upon its present lines so much the cheaper sort of thing does “fame” become, especially of the literary sort. This species of “fame” a waggish acquaintance says can be manufactured to order, and sometimes is so manufactured.”
—Herman Melville (1819–1891)
“Because a person is born the subject of a given state, you deny the sovereignty of the people? How about the child of Cuban slaves who is born a slave, is that an argument for slavery? The one is a fact as well as the other. Why then, if you use legal arguments in the one case, you don’t in the other?”
—Franz Grillparzer (1791–1872)
“Be reflective ... and stay away from the theater as much as you can. Stay out of the theatrical world, out of its petty interests, its inbreeding tendencies, its stifling atmosphere, its corroding influence. Once become “theatricalized,” and you are lost, my friend; you are lost.”
—Minnie Maddern Fiske (1865–1932)
“In the larger view the major forces of the depression now lie outside of the United States, and our recuperation has been retarded by the unwarranted degree of fear and apprehension created by these outside forces.”
—Herbert Hoover (1874–1964)