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Reproductive isolation between species appears, in certain cases, a long time after fertilization and the formation of the zygote, as happens – for example – in the twin species Drosophila pavani and D. gaucha. The hybrids between both species are not sterile, in the sense that they produce viable gametes, ovules and spermatozoa.
Reinforcement, under his definition, included prezygotic divergence and complete post-zygotic isolation. [18] Servedio and Noor include any detected increase in prezygotic isolation as reinforcement, as long as it is a response to selection against mating between two different species. [4]
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.
Support for the reproductive character displacement hypothesis comes from observations of sympatric species in overlapping habitats in nature. Increased prezygotic isolation, which is associated with reproductive character displacement, has been observed in cicadas of genus Magicicada, stickleback fish, and the flowering plants of the genus Phlox.
Ernst Mayr proposed the widely used Biological Species Concept of reproductive isolation in 1942. Most modern textbooks make use of Ernst Mayr's 1942 definition, [62] [63] known as the biological species concept, as a basis for further discussion on the definition of species. It is also called a reproductive or isolation concept.
The German evolutionary biologist Ernst Mayr argued in the 1940s that speciation cannot occur without geographic, and thus reproductive, isolation. [29] He stated that gene flow is the inevitable result of sympatry, which is known to squelch genetic differentiation between populations.
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 ...
Reproductive isolation occurs upon the formation of a hybrid zone. In most cases, [citation needed] the hybrid zone is eliminated due to a selective disadvantage. This effectively completes the speciation process. In parapatric speciation, two subpopulations of a species evolve reproductive isolation from one another while continuing to ...