Gametic isolation is a reproductive mechanism that can prevent hybridization from occurring. It can be difficult to understand, however, as there are other forms of reproductive isolation that work in similar ways.
In this article, we will define what gametic isolation is and provide examples of it in nature to make the process easier to understand.
What You Need To Know About Gametic Isolation
Gametic isolation is a form of reproductive isolation. Mating does occur in gametic isolation, but the male and female gametes are unable to bind together to form a zygote.
In fact, gamete isolation is the only type of prezygotic reproductive isolation where mating takes place at all. This is different from postzygotic reproductive isolation, where viable or fertile offspring are prevented from forming.
Gametic isolation is one of the five types of prezygotic reproduction that have been identified.
The process that causes populations to evolve into distinct species is called speciation. When speciation occurs, a single species splits into two and the two groups no longer share the same gene pool and are genetically different.
Many factors can cause speciation and gametic isolation is just one of them. Gametic isolation is a flexible thing, however, as it can also contribute to maintaining the integrity of a species as it prevents interbreeding.
There are also fewer chances of hybrid species being created with gametic isolation.
In short, gametic isolation prevents mating between distinct species. It is a mechanism of reproductive isolation that ensures gametes of different species from interacting with each other.
Through gametic isolation, gametes from different species are seen as being incompatible with each other, preventing the formation of hybrids.
How Does Gametic Isolation Work In Nature?
Let’s begin by quickly reviewing how sexual reproduction works within a species. It requires both a male gamete (a sperm cell) and a female gamete (an egg or ovum.)
The two gametes fuse together to produce an embryo, which in its earliest stages of development is known as a zygote. The zygote will only form if the sperm cell and egg/ovum are compatible with each other.
If the two sex gametes are not compatible in any way, then the fertilization will not happen and the zygote will not be formed.
This means that if the sperm cell of a male from species A comes into contact with the egg of a female from species B, the incompatibility and chemical compositions of the gametes will prevent fertilization from occurring.
Without fertilization, the hybrid zygote will not form.
Gametic reproductive isolation is seen in many species, but primarily in ones that have external reproduction, such as marine species and flowering plants.
For many marine species, sexual reproduction happens when the females release a batch of eggs into the water in a process known as broadcast spawning.
At the same time, the males of the species release sperm into the water which then fertilizes some of the eggs.
As you might imagine, as several different marine species reproduce in this manner, it is more than possible that the sperm of species A can come into contact with the eggs of species B.
Water carries the sperm around, increasing the chances of the sperm cells coming into contact with the eggs of a different species.
The chances of fusion between different species to form hybrids can happen in these circumstances, but this is where gametic isolation comes into play to prevent the hybrid zygotes from forming.
Examples Of Gametic Isolation
To further understand how gametic isolation works, let’s look at a couple of examples in nature of species that have not produced hybrids due to gametic isolation.
The west coast of the United States is home to two different species of sea urchins. These are the red sea urchin (Strongylocentrotus franciscanus) and the purple sea urchin (Strongylocentrotus purpuratus.)
They are known to share the same geographic locations and environment and are both species that breed by broadcast spawning. However, there is no evidence of the two sea urchin species interbreeding.
This is because their gametes are genetically incompatible, preventing hybrid fertilization.
A similar occurrence can be observed in the Caribbean sea. The Caribbean is home to several different species of coral that are related and share the same geographic locations.
These sympatric coral species even release their male and female gametes at the same time, however, instances of hybridization are very, very rare. This is due to gametic isolation.
It is very common for several different species of plants to share the same location and bloom side by side. Reproduction in plants occurs through pollination and involves the pollen grains from a male plant being transferred to the stigma of a female plant.
The male pollen is carried by either the wind or insects to another plant in the hope of meeting a stigma and causing pollination to occur.
These methods of transferring pollen occur at random, so it is very possible for the pollen of plant species A to meet the stigma of plant species B. However, the possibility of germination occurring is very, very rare due to gametic reproductive isolation.
There are some other instances where the pollen tube itself doesn’t correctly develop and this will also hinder fertilization.
Gametic reproductive isolation is a mechanism that prevents the male and female gametes of different species from fusing together to make a hybrid. As the sperm cell and egg are genetically incompatible, a zygote cannot form.
Gametic isolation can help to keep the integrity of a species and is also one mechanism of speciation.
Gametic isolation especially occurs in species that reproduce externally, such as marine animals and plants.
Sexual reproduction in these species involves an element of chance as the male, and often female, gametes are expelled in the hope of coming into contact with the opposite sex gamete.
Gametes of different species can easily come into contact in these circumstances, but gametic isolation prevents fertilization from occurring due to the incompatibility of the gametes.
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