For various species to separate from common ancestors and to drive evolution, reproductive isolation is needed. There are many types of reproductive isolation and they give rise to different species. The prezygotic isolation is the most common type; that occurs before fertilization between gametes and it does not allow different species to reproduce sexually.
Different types of prezygotic isolation occur, that range from incompatibility of gametes to change in behavior which results in mismatch.
Types of Isolations:
1. Mechanical Isolation
Mechanical isolation refers to the incompatibility of sexual organs; it is the simplest way to stop individuals from reproducing. The shape of the reproductive organs, the difference in their size, the location are the factors that prohibit individuals from coupling. The bottom line is that if the sexual organs are not fitting together, mating does not occur.
In plants, mechanical isolation is different as the size and shape are irrelevant to plant reproduction. It occurs from the use of a separate pollinator. For instance, in a plant bee pollination occurs, it will not give results if pollen grain is spread by hummingbirds. The undesired outcome is not due to different sizes here, but because of the incompatibility of the species.
2. Temporal Isolation
Species tend to have varying breeding seasons. The time of the female fertility cycle results in temporal isolation. Species that are alike may be physically compatible but can still not reproduce because of the differences in the mating seasons. For instance, the female species may be fertile at a particular time but the male species might not be able to reproduce at that time, which leads to reproductive isolation.
At times, the mating seasons of similar species overlap. This is possible if the species live in different areas and leave no chance for hybridization. It has been shown that similar species living in the same area usually do not overlap in mating; but if they do when in different environments. This is an adaptation nature which reduces the competition for mates and resources.
3. Behavioral Isolation
This type of isolation occurs between species with different behaviors. Particularly, the behaviors around mating time. If populations of two different species are mechanically and temporally compatible, the mating behavior is vital to keep the species in reproductive isolation from each other.
The mating rituals and mating behaviors are important for males and females of the same species; this indicates that it is the right time to reproduce. If the mating ritual is not recognized, then mating does not occur and the species are said to be reproductively isolated from one another.
An example of this is the blue-footed booby bird which has a mating dance that the male performs to woo the female. The female can accept or reject the advances of the male. The other bird species which do not have the same mating dance are ignored by the female blue-footed booby. That is, the other species cannot reproduce with this blue-footed booby female bird.
4. Habitat Isolation
The related species have preferences with respect to where they shall live and where they reproduce. The preferred locations are not compatible between species; this leads to habitat isolation. If the individuals of different species do not live close to each other; hence, there will be no opportunity to reproduce. This type of reproductive isolation leads to speciation.
Different species living in the same area may also be incompatible due to differences in the preferred place of reproduction. Some birds prefer a certain type of tree, different parts of the same tree, for laying the eggs and making nests.
5. Gametic Isolation
Gametic isolation helps in ensuring that sperm of the same species only can penetrate the egg of that species. During sexual reproduction, the female egg gets fused with the male sperm and forms a zygote. If the egg and the sperm are not compatible, fertilization does not occur. Due to the chemical signals released by the egg, a sperm may not attract towards it.
The other factor that avoids fusion is a sperm that cannot penetrate the egg because of its chemical composition. The above two reasons are sufficient to not cause fusion and prevent the formation of zygote.
This reproductive isolation is important for species that reproduce in water externally. For example, the female species of many fishes release the eggs in the water where they prefer breeding. The male fish of the species then release their sperm over the distributed eggs and lets them. This takes place in a liquid environment, so, some sperm gets swept away due to the water molecules and are dispersed. With no gametic isolation mechanism, any sperm fuses with an egg and results in hybrid species that is a combination of the species that mated in the water at that time.
FAQs:
- What is reproductive isolation?
It refers to species living around but is unable to reproduce. - Why does Reproductive isolation occur?
It is caused by sterility, the difference in mating and environmental barriers. - What is isolation precaution?
It is used to stop the spread of germs from person to person.
