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Hybrid zones can form from secondary contact. A hybrid zone exists where the ranges of two interbreeding species or diverged intraspecific lineages meet and cross-fertilize. . Hybrid zones can form in situ due to the evolution of a new lineage [1] [page needed] but generally they result from secondary contact of the parental forms after a period of geographic isolation, which allowed their ...
Conversely, if the hybrid offspring are more fit than their ancestors, then the populations will merge back into the same species within the area they are in contact. [citation needed] Another important theoretical mechanism is the arise of intrinsic genetic incompatibilities, addressed in the Bateson-Dobzhansky-Muller model. [49]
Genes that are incompatible according to the Dobzhansky–Muller model require three criteria. 1. The gene reduces the fitness of the hybrid, 2. The gene has functionally diverged in each of the hybridising species and, 3. The hybrid incompatibility is only present in combination with a partner gene. [6]
A hybrid zone may appear during secondary contact, meaning there would be an area where the two populations cohabitate and produce hybrids, often arranged in a cline. The width of the zone may vary from tens of meters to several hundred kilometers. A hybrid zone may be stable, or it may not.
Mathematical models, laboratory studies, and observational evidence supports the existence of parapatric speciation's occurrence in nature. The qualities of parapatry imply a partial extrinsic barrier during divergence; [2] thus leading to a difficulty in determining whether this mode of speciation actually occurred, or if an alternative mode (notably, allopatric speciation) can explain the data.
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For a hybrid form to persist, it must be able to exploit the available resources better than either parent species, which, in most cases, it will have to compete with.For example: while grizzly bears and polar bears may be able to mate and produce offspring, a grizzly–polar bear hybrid is apparently less- suited in either of the parents' ecological niches than the original parent species ...