Reproductive Isolation: Definition, Types, Examples and Process

Reproductive isolation is a crucial concept that refers to the mechanisms that prevent different species or populations from interbreeding. These barriers ensure that genes are not exchanged between populations, leading to genetic divergence over time. It plays a significant role in the formation of new species. This process is directly linked to speciation and evolution as reproductive isolation helps to maintain and create distinct gene pools.

This Story also Contains

1. What Is Reproductive Isolation?
2. Mechanisms Of Reproductive Isolation
3. Examples Of Reproductive Isolation In Nature
4. Role Of Reproductive Isolation In Speciation
5. Recommended video for "Reproductive Isolation"
6. MCQs on Reproductive Isolation

In evolution, reproductive isolation helps explain how species adapt and change over generations. By limiting gene flow between populations, it allows unique traits to develop based on environmental pressures or genetic drift. Understanding reproductive isolation is essential to grasping how biodiversity arises and is maintained in nature

What Is Reproductive Isolation?

Scheidung describes those factors that increase species diversity and ensures that the individuals of one species do not interbreed with those of another species to produce viable offspring. This concept is essential in evolutionary biology since it assists in the identification of how new species develop and in the explanation of how variation of genes are retained across generations.

There are several ways in which reproductive isolation can be presented such as pre-mating barriers where there is no possibility of the two featuring and or mating and post-mating barriers where there are reduced chances of the offspring germinating. Knowledge of these mechanisms gives information about the processes of formation of new species and the preservation of biotic diversity.

Mechanisms Of Reproductive Isolation

Reproductive isolation occurs through several mechanisms that prevent mating or the production of fertile offspring. These mechanisms are categorized as prezygotic and postzygotic. Prezygotic barriers include habitat isolation, behavioral differences, and mating time differences. Postzygotic barriers include hybrid sterility or reduced viability. These mechanisms help maintain species boundaries.

Prezygotic Barriers

These are reproductive barriers that prevent fertilization from occurring between different species. They act before the formation of a zygote. These barriers include:

Postzygotic Barriers

These barriers occur after fertilization, leading to the inviability or infertility of the resulting offspring. Examples include hybrid sterility (e.g., mule) or hybrid breakdown. These barriers include the following:

Examples Of Reproductive Isolation In Nature

Reproductive isolation can be observed among closely related species. For example, different frog species may live in the same area but breed at different times, preventing interbreeding. Birds may use different songs to attract mates, leading to behavioral isolation. These examples show how isolation maintains diversity. The examples are listed below-

Darwin's Finches

The famous case of reproductive isolation driving the process of speciation is that of Darwin’s finches of the Galápagos Islands. For instance, various species of finches developed different mechanisms and sizes of beakers about the island food resource base that was available. These differences in the beak structure and songs are examples of prezygotic isolations whereby no two species can interbreed for even if the female lays her eggs in the male’s nest, they will not hatch, thus showing how geographic and behavioural barriers play a significant role in forging new species.

Eastern and Western Meadowlarks

The two species that seem closely related are the Eastern and Western meadowlarks but they are reproductively isolated through prezygotic isolation mainly by the disharmonizing sounds. Despite the ranges and contact calls often overlapping, there appear to be species-specific calls used in mate selection which help to reduce cases of interbreeding. This behavioural isolation is for species perseverance since only individuals with the same mating calls reproduce.

Lions and Tigers (Ligers and Tigons)

Lions and tigers can't be in the same pride since lions are larger than tigers However, ligers are obtained where a male lion mates with a tiger female and tigons come from a tiger male and a lion female. These hybrids are often feasible but crop up with the problem of low fecundity. A liger is bigger than the parent species, but it cannot mate due to infertility, which is inherited from the lion's mother. This example sheds light on the fact that though there are occasional hybrids, postzygotic barriers such as problems with fertility, prevent the two species from interbreeding and thus remain distinct.

Role Of Reproductive Isolation In Speciation

Reproductive isolation helps in speciation,the process through which new species evolve. When two populations become reproductively isolated, they can no longer exchange genes. Over time, genetic differences accumulate due to mutation, natural selection, and genetic drift. Reproductive isolation thus helps explain how biodiversity increases through evolution.

Allopatric Speciation

• Allopatric speciation is the process by which new species are formed because of the geographical isolation of the populations.

• Physical barriers include factors that hinder the movement of genes from one population to another for instance mountains or rivers.

Sympatric Speciation

• Sympatric speciation is the kind of speciation that takes place with no geographical isolation but might be through ecological opportunities and sexual selection.

• For example, variation in mating preference or sources of food may cause the formation of new species.

Parapatric Speciation

• In parapatric speciation, populations are situated near each other, but the two groups interact very little due to some barriers.

• Lower gene exchange results in new species at the boundaries of various geographic populations.

Recommended video for "Reproductive Isolation"

MCQs on Reproductive Isolation

Q1. Which type of premating isolating mechanism will select a mating partner within a species?

1. Temporal isolation

2. Behavioral isolation

3. Electrical isolation

4. Reproductive isolation

Correct answer: 2) Behavioral isolation

Explanation:

Option 2 is correct because the mating partner selecting a potential mate from their species is known as behavioural isolation.

Option 1 is incorrect because Temporal isolation occurs when individuals of different species do not mate because they are active during different seasons.

Options 3 and 4 are incorrect because they do not involve the premating isolating mechanism.

Hence, the correct answer is option 2) Behavioral isolation.

Q2. Which type of premating isolating mechanism will copulate without the transfer of sperm?

1. Reproductive isolation

2. Behavioral isolation

3. Mechanical isolation

4. Temporal isolation

Correct answer: 3) Mechanical isolation

Explanation:

Option 3 is correct because successful copulation without sperm transfer is known as mechanical isolation.

Option 2 is incorrect because the mating partner selecting a potential mate from their species is known as behavioral isolation.

Option 4 is incorrect because temporal isolation occurs when individuals of different species do not mate because they are active during different seasons.

Option 1 is incorrect because not involved in the premating isolating mechanism

Hence, the correct answer is option 3) Mechanical isolation.

Q3. Among the listed options, which combinations exclusively represent pre-zygotic forms of reproductive isolation?

a. Hybrid inviability

b. Gametic isolation

c. Zygote mortality

d. Temporal isolation

1. a, b, d
2. b, d
3. Only d
4. a, c

Correct answer: 2) b, d

Explanation:

Pre-zygotic reproductive isolation refers to barriers that prevent successful fertilization between individuals of different species or populations. These barriers occur before the formation of a zygote, which is the fertilized egg.
Gametic isolation (option 2) is a pre-zygotic form of reproductive isolation where the gametes (sperm and egg) of different species or populations are incompatible, preventing fertilization from taking place.

Temporal isolation (option 4) is another pre-zygotic form of reproductive isolation. It occurs when different species or populations have different breeding times or mating seasons, preventing them from encountering each other and attempting to reproduce.

The correct answer is option 2 "b and d," is the correct answer because it exclusively represents pre-zygotic forms of reproductive isolation, involving both gametic isolation and temporal isolation.

Hence the correct answer is Option 2) b, d.

Also Read:

• MCQs on Reproductive Isolation

• Embryology

• Adaptive Radiation