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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]
Examples of pre-zygotic isolation include habitat isolation, isolation via pollinator-pollination systems, and temporal isolation. Examples of post-zygotic isolation involve genetic incompatibilities of hybrids , low fitness hybrids, and sexual selection against hybrids.
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).
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.
Assuming all goes well, Torres said the president, who is 74, should be out of isolation on Oct. 12, provided he doesn't exhibit any symptoms before then. Quarantine vs. isolation: What to know ...
Reproductive isolation between a hybrid species and its parental species can arise from a variety of reproductive barriers either before or after fertilization (prezygotic or postzygotic, respectively), which may themselves be dependent or independent of environmental conditions (extrinsic or intrinsic barriers, respectively). [77]