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The magic of genes: How to prevent species from mating forever?
In evolutionary biology, reproductive isolation mechanisms are a series of behavioral and physiological processes that are critical to the formation of species. These mechanisms prevent the production of offspring between different species or ensure that any offspring are incompetent. These barriers reduce gene flow between related species, thus maintaining species integrity. The mechanisms of reproductive isolation have been classified many times, and it is critical to further understand how these mechanisms work.
“The impact of the reproductive isolation mechanism on species evolution cannot be underestimated. Diversity from physiology to behavior allows species to persist in nature.”
Preliminary isolation mechanism
Pre-isolation mechanisms, which operate before fertilization, are the most economical because resources are not wasted producing weak, inactive, or incompetent offspring. These mechanisms include physiological or systemic disorders that prevent fertilization from occurring.
Temporal or habitat isolation
Factors that prevent potential breeding individuals from meeting each other can lead to reproductive isolation in different species. These types of isolation include different habitats, physical barriers, and differences in mating or flowering times. For example, two species of springtails cannot mate because they live in different environments. One lives in freshwater environments and the other breeds in the ocean.
Behavioral isolation
"Animal mating rituals play an extremely important role in distinguishing species, and behavioral isolation is often the main obstacle between species."
A species' mating rituals play a key role in behavioral isolation, especially when males and females are required to engage in complex courtship behaviors. Examples of such isolation include insect sex pheromones, chemicals that are used to identify individuals of a species, further preventing interbreeding.
Mechanical isolation
If the reproductive organs of mating partners are incompatible, successful mating may not occur. The mating organs of many species have evolved different shapes and structures through the process of natural selection, further leading to the creation of mechanical isolation.
Later isolation mechanism
The late isolation mechanism occurs after fertilization and mainly includes the following situations:
Zygotic death and hybrid inactivity
“Hybrid offspring may have normal viability but often fail to reproduce due to a genetic mismatch between species.”
For example, after the zygote is formed in a cross between different frog species, the offspring will show low vitality or inactivity due to genetic incompatibility.
Hybrid sterility
Crossing may produce offspring that are lively but sterile. Common crosses, such as those between horses and donkeys, produce camels, but these camels are almost always unable to reproduce because of a mismatch in the number of chromosomes between the parent species.
"Reproductively sterile hybrids are also common in the plant world. Although such hybrids can form the basis of new species, they often fail to produce reproductive capabilities."
The role of multiple mechanisms
In fact, the barriers that separate species often consist of more than just a single mechanism. Taking fruit flies as an example, the reproductive isolation between Drosophila pseudobscura and Drosophila persimilis includes differences in habitat, mating season, and mating behavior. These composite mechanisms allow them to maintain differentiation despite overlapping geographical distributions.
"Isolation between species is the key to biological evolution. It is related to both genes and behavior, and has far-reaching effects in nature."
So, as we delve deeper into these mechanisms of reproductive isolation, can we find effective ways to further advance species conservation?
