In this article we will discuss about the meaning and mechanisms of isolation of species.
Meaning of Isolation:
The first step in the development of a new species is isolation. A population should split up into two or more separate demes each with its own gene pool. These demes must be isolated from one another. If genes are exchanged between them they will effectively behave as one population.
If they are isolated, mutation and selection can operate independently in the two populations and each can develop into a distinct species.
Mechanisms of Isolation:
There are three isolating mechanisms important that can lead to the origin of new species:
1. Geographical Isolation:
Frequently isolation is geographic. The population may be widely separated geographically or divided by impenetrable barriers such as mountain ranges and rivers. Even if they occupy the same locality they may be separated by having a preference for slightly different habitats. This is also called as ecological isolation.
2. Reproductive Isolation:
Even though two populations may not be ecologically separated, they may be effectively isolated by reproductive isolation i.e. they cannot interbreed. This might be caused by lack of attraction between males and females or by physical non-correspondence of genetalia.
In case of flowering plants it may be due to the fact that pollination is impossible between the two populations. In animals with elaborate behaviour patterns, it may be because the courtship behaviour of one fails to stimulate the other. This is also called as behavioural isolation.
3. Genetic Isolation:
Some times mating may be possible, but reproduction is not possible because of fundamental differences in genetic constitution. Thus, the gametes may be prevented from fusing. For example, the pollen grain of one population of plants, may fail to germinate on the stigmas of the other.
Even if fertilization does occur, the zygote may be inferior in some way and fail to develop properly. Sometimes offsprings are produced but the hybrids may be adaptively inferior, living only for a short time.