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Hybrid speciation
Hybrid speciation is a form of speciation wherein hybridization between two different species leads to a new species, reproductively isolated from the parent species. From the 1940s, reproductive isolation between hybrids and their parents was thought to be particularly difficult to achieve and thus hybrid species were thought to be extremely rare. With DNA analysis becoming more accessible in the 1990s, hybrid speciation has been shown to be a fairly common phenomenon, particularly in plants.〔Wendel, J F. & Doyle, J.J. (1998): DNA Sequencing. In ''Molecular Systematics of Plants II''. Editors: D.E. Soltis, P.S. Soltis, J.J. Doyle. Kluwer, Boston, pp. 265–296.〕
In botanical nomenclature, a hybrid species is also called a nothospecies.〔 Article H.1〕 Hybrid species are by their nature polyphyletic.
==Hybrid speciation ecology==
A hybrid may have a distinct trait (phenotype). This phenotype may in very rare cases be better fitted to the local environment than the parental lineage and as such natural selection may favor these individuals. If reproductive isolation subsequently is achieved, it will lead to a separate species. The reproductive isolation may be genetic, ecological, behavioural, or spatial, or a combination of these.
If reproductive isolation fails to establish, the hybrid population may breed back and finally merge with either or both parent species. This will lead to an influx of foreign genes in the parent population, a situation called an introgression. Introgression is a source of genetic variation, and can in itself facilitate speciation. There is evidence that introgression is a ubiquitous phenomenon in plants, animals, and even humans, where genetic material from Neanderthals and Denisovans is responsible for much of the immune genes in non-African populations.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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