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The mechanisms of reproductive isolation have been classified in a number of ways. Zoologist Ernst Mayr classified the mechanisms of reproductive isolation in two broad categories: pre-zygotic for those that act before fertilization (or before mating in the case of animals) and post-zygotic for those that act after it. [5]
Hybrid dysfunction (sterility and inviability) is a major form of post-zygotic reproductive isolation, which occurs in early stages of speciation. Evolution can produce a similar pattern of isolation in a vast array of different organisms. However, the actual mechanisms leading to Haldane's rule in different taxa remain largely undefined.
The Bateson–Dobzhansky–Muller model, [1] also known as Dobzhansky–Muller model, is a model of the evolution of genetic incompatibility, important in understanding the evolution of reproductive isolation during speciation and the role of natural selection in bringing it about.
Reinforcement is a process of speciation where natural selection increases the reproductive isolation (further divided to pre-zygotic isolation and post-zygotic isolation) between two populations of species. This occurs as a result of selection acting against the production of hybrid individuals of low fitness.
The species contact zones exhibit, "strong postzygotic selection against hybrids" and enhanced isolation from differences in mating call. [ 13 ] An alternative to detecting reproductive character displacement in populations that overlap in sympatry is measuring rates of hybridization in contact zones. [ 9 ]
Pre-zygotic reproductive isolation means that the reproducing individuals in the populations were unable to produce offspring (effectively a positive result). Post-zygotic isolation means that the reproducing individuals were able to produce offspring but they were either sterile or inviable (a positive result as well). Negative results are ...
Hybrid inviability is a post-zygotic barrier, which reduces a hybrid's capacity to mature into a healthy, fit adult. [1] The relatively low health of these hybrids relative to pure-breed individuals prevents gene flow between species.
Examples of post-zygotic isolation involve genetic incompatibilities of hybrids, low fitness hybrids, and sexual selection against hybrids. Some debate exists over the framework concerning the delineation of whether a speciation event is ecological or nonecological.