Segregation of the population of a species into small units or strains or subspecies so that they become unable to interbreed is termed as isolation. They sub units become unable to breed with the ancestral species and lead to the formation of new species. This isolation is due to some physical or geographical or other barrier.
Wagner explained the significance of isolation. Metcalf stated that the factors that prevent interbreeding and isolate into small groups are called as isolation factors. According to Kellog isolation is a biological catalyst that facilitate changes among the animals.
The Darwin finches found in Galapagos island are the result of isolation.
Types of Isolation-
(A) Geographical isolation:
Geographical barriers play an important role in the process of speciation. Such as Oceans, Sea, Desert, Dense forest, Mountains and Hills etc. The animals become unable to cross such barriers and fail to interbreed. Every group adapt itself by developing changes. Example: Darwin finches.
(B) Spacial Isolation:
In this type of isolation, there is no geographical barrier in between the animal groups but because of long distances the animal groups become unable to interbreed. For example one species of elephant seal inhabit South pole and second species inhabit North America. The big distance between two keep them isolated.
(C) Reproduction Isolation:
Many animals are biologically deficit and are unable to reproduce. It is called as reproductive or biological isolation. It is of two types
(a) Pre-zygotic Isolation The animals are unable to form zygotes due to some biological abnormalities
It is of following types-
- Habitat or Ecological Isolation The animals are unable to breed due to different habitat or ecological conditions.
- Seasonal Isolation – Animals living in the same habitat get unable to breed but to difference in the breeding season.
- Morphological Isolation – Animals become unable to breed due to difference in the shape.
- Physiological Isolation – The reproductive organs & their physiology is species specific. Hence, the animals of different species are unable to breed though they live in same habitat.
(b) Post-zygotic Isolation
Sometimes, the animals of different species may breed but their zygote fails to develop further and normally dies. It is called as zygotic mortality. Sometime, such zygote develop to form hybrid but such hybrid either die or become sterile, For example, the Horse & Donkey interbreed to produce sterile Mule.
Significance of Isolation:
On the earth, origin of new species is the result of evolution and the isolation play impotent role in this process. The isolation prevent interbreeding & help in natural selection. The isolation also prevent the transmission of useless & harmful genes into the animals.
