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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 ...
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.
An example of a homoploid hybrid genome is a schematic of the mosaic genome of the Italian sparrow which is a hybrid resulting from the house sparrow P. domesticus which spread across the Mediterranean with agriculture and encountered and hybridized with local populations of Spanish sparrow P. hispaniolensis [48,49,85].
Hybrid zones are regions where diverged populations meet and interbreed. Hybrid offspring are common in these regions, which are usually created by diverged species coming into secondary contact . Without reinforcement, the two species would have uncontrollable inbreeding .
A prediction of reinforcement is that assortive mating should be common in hybrid zones; a prediction that was confirmed in 19 of the 37 cases. [6] A survey of the rates of speciation in fish and their associated hybrid zones found similar patterns in sympatry, supporting the occurrence of reinforcement. [68]
In other cases, selection may favor multiple and varying phenotypes [26] such as in the case of a mosaic hybrid zone. [31] Natural selection can act on specific alleles both directly or indirectly. [ 29 ] [ 22 ] [ 34 ] In direct selection, the frequency of the selected allele is favored to the extreme.
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 ...