What are the different types of isolating mechanisms?

A number of isolating mechanisms are operated in nature and therefore divergence and speciation may occur.
The isolating mechanisms are of two types namely, geographical isolation and reproductive isolation.

1. Geographical Isolation:

It is also called as physical isolation. It occurs when an original population is divided into two or more groups by geographical barriers such as rivers, oceans, mountains, glaciers, etc. These barriers prevent interbreeding between isolated groups.

The separated groups are exposed to different kinds of environmental factors and they acquired new traits by mutations. The separated populations develop distinct gene pool and they do not interbreed. Thus, new species have been formed by geographical isolation. e.g. Darwin’s Finches.

2. Reproductive Isolation:

Reproductive isolation occurs due to change in genetic material, gene pool and structure of genital organs. It prevents interbreeding between populations. Types of Isolating Mechanisms:

a. Pre-mating or pre-zygotic isolating mechanism:

This mechanism prevents fertilization and zygote formation.

i. Habitat isolation or (Ecological isolation): Members of a population living in the same geographic region but occupying separate habitats in such a way that potential mate do not meet.

ii. Seasonal or temporal isolation: Members of a population living in the same geographic region but are sexually mature at different years or different times of the year.

iii. Ethological isolation: Due to specific mating behavior the members of the population do not mate.

iv. Mechanical Isolation: Members of two populations have a difference in the structure of reproductive organs.

2. Post-mating or Post-zygotic barriers:

i. Gamete mortality: Gametes have a limited life span. Due to one or the other reasons, if the union of the two gametes does not occur in the given time, it results in gamete mortality.

ii. Zygote mortality: Here, egg is fertilized but the zygote dies due to one or the other reasons.

iii. Hybrid sterility: Hybrids develop to maturity but become sterile due to the failure of proper gametogenesis (meiosis).
e.g. Mule is an inter-generic hybrid that is sterile.

Understanding:

•  Reproductive isolation of populations can be temporal, behavioural or geographic

    
Reproductive isolation occurs when barriers prevent two populations from interbreeding – keeping their gene pools separate

There are two main categories of reproductive isolation barriers:

• Prezygotic isolation – occurs before fertilisation can occur (no offspring are produced)
• Postzygotic isolation – occurs after fertilisation (offspring are either not viable or infertile)

Prezygotic isolation barriers can be temporal, behavioural, geographic / ecological or mechanical; whereas postzygotic isolation barriers include the inviability, infertility or breakdown of hybrid organisms

Reproductive Isolation Mechanisms

Temporal Isolation

• Temporal isolation occurs when two populations differ in their periods of activity or reproductive cycles
• Example:  Leopard frogs and wood frogs reach sexual maturity at different times in the spring and hence cannot interbreed

Behavioural Isolation

• Behavioural isolation occurs when two populations exhibit different specific courtship patterns
• Example:  Certain populations of crickets may be morphologically identical but only respond to specific mating songs

Geographic Isolation

• Geographic isolation occurs when two populations occupy different habitats or separate niches within a common region
• Example:  Lions and tigers occupy different habitats and do not interbreed (usually)

Types of Reproductive Isolation

The field of biology describes "isolation" as a process by which two species that could otherwise produce hybrid offspring are prevented from doing so. There are five isolation processes that prevent two species from interbreeding: ecological, temporal, behavioral, mechanical/chemical and geographical.

TL;DR (Too Long; Didn't Read)

There are five types of isolation that biologically prevent species that might otherwise interbreed to produce hybrid offspring. These are ecological, temporal, behavioral, mechanical/chemical and geographical.

Ecological Isolation

Ecological, or habitat, isolation occurs when two species that could interbreed do not because the species live in different areas. For example, in India both the lion and tiger exist and are capable of interbreeding; however, the lion lives in the grasslands and the tiger lives in the forest. The two species live in different habitats and will not encounter one another: each is isolated from the other species.

Temporal Isolation

Temporal isolation is when species that could interbreed do not because the different species breed at different times. This temporal difference could occur at difference times of day, different times of the year, or anything in between. For example, the field crickets Gryllus pennsylvanicus and G. veleti become sexually mature at different seasons, one in the spring and the other in the autumn.

Behavioral Isolation

Behavioral isolation refers to the fact that many species perform different mating rituals. This is a common barrier between animals. For example, certain species of crickets will only mate with males that produce a particular mating song. Other species rituals may include a mating dance or emitting a scent. These clues are ignored by species not accustomed to the ritual.

Mechanical or Chemical Isolation

Mechanical isolation is caused by structures or chemical barriers that keep species isolated from one another. For example, in flowering plants, the shape of the flower will tend to match up with a natural pollinator. Plants that do not have the correct shape for the pollinator will not receive a pollen transfer. Likewise, certain chemical barriers prevent gametes from forming. These chemical barriers will only allow sperm from the correct species to fertilize the egg.

Geographical Isolation

Geographical isolation refers to the physical barriers that exist that keep two species from mating. For example, a species of monkey that is located on an island cannot breed with another species of monkey on the mainland. The water and distance between the two species keep them isolated from one another and make it impossible for them to breed.

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