Over time, mutations then build up and new adaptations become evident, making new species that came from a common ancestor. There are many different isolating mechanisms, called prezygotic isolations , that prevent species from interbreeding with each other. If they do manage to produce offspring, there are more isolating mechanisms in place, called postzygotic isolations , that ensure the hybrid offspring are not selected for by natural selection.
In the end, both types of isolations are designed to drive evolution and make sure that speciation is the desired outcome. Which types of isolations are more effective in the view of evolution? Are prezygotic or postzygotic isolations the preferred deterrent for species interbreeding and why? While both are very important, they have their strengths and weaknesses in speciation. The biggest strength of prezygotic isolations is that it prevents a hybrid from even happening in the first place.
Since there are so many prezygotic isolations mechanical, habitat, gametic, behavioral, and temporal isolations , it stands to reason that nature prefers these hybrids not even form in the first place. There are so many checks and balances in place for prezygotic isolation mechanisms, that if species manage to avoid being caught in the trap of one, then another will prevent the hybrid of the species from forming. This is especially important to prohibit mating between very different species.
However, especially in plants, hybridization does occur. Usually, this hybridization is between very similar species that have much more recently diverged into different lineages from a common ancestor in the relatively recent past. If a population is divided by a physical barrier that leads to speciation due to the individuals not being able to get to each other physically, they are more likely to form hybrids.
In fact, there is often an overlap of habitat called the hybridization zone where this type of interaction and mating occurs. So while prezygotic isolation is very effective, it cannot be the only type of isolation mechanism in nature. When prezygotic isolation mechanisms fail to keep species in reproductive isolation from each other, the postzygotic isolations will take over and ensure that speciation is the preferred route for evolution and diversity among species will continue to increase as natural selection acts.
In postzygotic isolation, hybrids are produced but tend not to be viable. They may not survive long enough to be born or have major defects. If the hybrid makes it to adulthood, it is often sterile and cannot produce its own offspring.
Species is a reproductively isolated group. Prezygotic and postzygotic are two main reproductive isolation mechanisms. The reproductive isolation that occurs before fertilization is the prezygotic isolation.
While, the reproductive isolation that occurs after fertilization and prevents the fertilized egg to become a fertile offspring is the post-zygotic isolation. Overview and Key Difference 2. What is Reproductive Isolation 3. What is Prezygotic Isolation 4. What is Postzygotic Isolation 5. Similarities Between Prezygotic and Postzygotic 6.
Reproductive isolation refers to a set of mechanisms that prevent species or the members of the same group from breeding or mating with each other. Thus, it prevents the production of fertile offspring.
Several mechanisms are responsible for reproductive isolation. Among them, prezygotic and postzygotic are two main mechanisms. Prezygotic reproductive isolation is a mechanism of reproductive isolation that prevents the fertilization of the eggs.
There are different categories of prezygotic isolation mechanism. Therefore, postzygotic isolation mechanisms such as zygote mortality, non-viability of hybrids, and hybrid sterility make the hybrid not viable. Thus, the hybrid may not either be born, have major defects or may be sterile.
Ultimately, postzygotic isolation prevents the formation of an offspring by the hybrids. Figure 2: Mules are Hybrids with Interspecific Sterility. Moreover, the main disadvantage of postzygotic isolation is that it has to rely on natural selection to correct the convergence of species. When this does not occur, hybrids regress from the evolutionary timeline, reverting to a more primitive species. Prezygotic isolation refers to the type of reproductive isolation that occurs before the formation of the zygote.
Postzygotic isolation refers to the second type of reproductive isolation which occurs after the production of the zygote. No mating occurs in the prezygotic isolation while mating occurs in the postzygotic isolation. Prezygotic isolation is an extrinsic mechanism that permits the physical isolation of parents, and thus, preventing mating. But, postzygotic isolation is an intrinsic mechanism which does not allow the formation of an offspring through the formation of hybrids.
Moreover, prezygotic isolation can evolve as mating signals and preferences adapt to different environments. Postzygotic isolation, on the other hand, evolves since hybrids have intermediate phenotypes and are poorly adapted to parental habitats. While prezygotic isolation depends on the environment, postzygotic isolation does not depend on the environment. Prezygotic isolation does not occur through genetic incapabilities , but postzygotic isolation occurs through genetic incapabilities , which in turn cause sterility.
Habitat isolation, behavioral isolation, mechanical isolation, and gametic isolation are the mechanisms that result in prezygotic isolation.
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