Hybrid speciation

Hybrid speciation is the process wherein hybridization between two different closely related species leads to a distinct phenotype. This phenotype in very rare cases can also be fitter than the parental lineage and as such natural selection may then favor these individuals. Eventually, if reproductive isolation is achieved, it may lead to a separate species. However, reproductive isolation between hybrids and their parents is particularly difficult to achieve and thus hybrid speciation is considered an extremely rare event.

Hybridization without change in chromosome number is called homoploid hybrid speciation. It is considered very rare but has been shown in "Heliconius" butterflies and in sunflowers. Polyploid speciation, which involves changes in chromosome number, is a more common phenomena, especially in plant species.

In most cases however nature has its own interspecies genetic barriers to guard against genetic pollution to keep species distinct. When rarely hybridization does occur naturally as in hybrid zones where the ranges of closely related wild species overlap, the hybrid crosses produced, even though they may display hybrid vigour (heterosis) in the first generation (F1 hybrid), are in the long run less fit than the two parent species which have evolved over hundreds of thousands of years specializing in exploiting their own particular niche in nature. It is extremely rare that the hybrids ever become fitter than the two wild parent species so that natural selection may then favor these individuals and it is even more extremely rare that reproductive isolation is ever achieved to lead to the birth of a new species through the process known as Hybrid speciation.

ee also

*Mariana Mallard
*Genetic pollution

References

* Mavarez, J., Salazar, C.A., Bermingham, E., Salcedo, C., Jiggins, C.D. , Linares, M. (2006) Speciation by hybridization in Heliconius butterflies. Nature.