Definition of Allopatric Speciation
The word allopatric comes from the Greek language. Allopatric is a word that signifies "geographical." Geographic speciation, dumbbell model, and vicariant speciation are all terms used to describe allopatric speciation. So, what exactly is allopatric speciation? In layman's terms, it refers to the speciation of two populations of the same species that have gotten isolated from one another due to geographic barriers. Speciation is the gradual transformation of populations into new species.
Determination of Sympatric Speciation
occurs when new species emerge from an original population that is not geographically separated or has no barriers. The sympatric speciation notion distinguishes itself from other types of speciation in that new species emerge from livings that are found in highly overlapping and indistinguishable areas. Furthermore, because bacteria pass their DNA both within their community and to progeny when they reproduce, this sort of speciation is highly common in bacteria.
Allopatric Speciation Steps
It is a well-known truth that before the process of speciation began, there was a population of species that shared the same features and had complete freedom to mate with one another. As a result, a habitat always contained the same collection of individuals. The fundamental reason for allopatric speciation, as previously stated, is the geographical barrier that is built between populations of the same uniqueness, causing them to no longer be classed as the same species.
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Parallel Evolution
Selection as the driving force in divergence and speciation is supported by parallel evolution and parallel speciation. Many alleged examples have been discovered in nature. However, much work remains to be done - separating parallelism from a single origin, for example, can be challenging.
More clarity will be gained through advances in modelling and experimental approaches. There's also a lack of data on how often identical selection forces lead to parallel evolution, as opposed to occasions where evolution discovers wholly alternative solutions to the same problem.
We are beginning to comprehend the genetic foundation of parallel evolution, but much more research is needed to determine the relative contributions of standing genetic variation, novo mutation, and gene flow to genetic change, as well as the function of constraints and stochasticity.
What is Speciation?
A species is a group of organisms showing similar features and can interbreed among themself to produce their offspring. Whereas speciation is a process of formation of new species from existing species as they evolve due to certain factors like geographical factors. The formed species are reproductively isolated from their previous species i.e, they cannot interbreed among themselves.
Factors Affecting Speciation Process
There are many factors that lead to speciation in the environment, they are
Geographical Isolation: When a certain number of species move to different areas and due to this factor they cannot interbreed among themself due to several obstacles like mountains rise, continental drift, organism mate, etc and this leads to speciation.
Reduction of Gene Flow: in the case when two individuals are not able to mate because of several factors then there are chances of reduced gene flow but not total isolation.
Hybridisation: Hybridization is an artificial method of developing a new species. In animal husbandry, two parents from different species are mated to form a third species. Hybridization has numerous and various impacts on the process of speciation.
Advantages of Speciation
There are several advantages of speciation they are:
Speciation teaches organisms to live under adverse conditions.
It enriches the ecological balance of abiotic and biotic components.
Disadvantages of Speciation
Cannot be taken for fossil records.
Absent in asexual species.
Only applied to populations that are geographically isolated.
Allopatric Speciation
This type of speciation happens when two populations of the same species become isolated from each other due to geographic factors. Speciation is a slow process due to which populations evolve into different species. A species is defined as a population that can interbreed among itself, so during the speciation process the population form two or more distinct species that can no longer interbreed among themselves.
Example of Allopatric Speciation:
Darwin's Finches
It is a major example of allopatric speciation that occurs in Galapagos finches that Charles darwin. In total there are 15 types of finches on the Galapagos islands and all of them have specific features like beaks for eating different types of food, but all finches have common ancestors, because of isolation to different islands they evolved. The birds who survive successfully become prevalent in their environment and form a variety of species. This evolution is known as adaptive evolution.
Grand Canyon Squirrels
When they are formed they create a natural barrier between the squirrels living in the area. Squirrel populations were separated due to geographical changes and they got distributed in different areas and became two different species.
Sympatric Speciation
Speciation occurs when two groups of the same species live in the same geographical location, but they evolve differently till they can no longer interbreed and are considered as different species. This type of speciation is seen in different types of organisms like bacteria, fish, apple maggot fly. But it is difficult to find when sympatric evolution occurred or occurred in nature. It evolves the population of new species when they are divided by geographical barriers. This evolution happens without any geographical isolation, under this evolution change in chromosomes occurs.
There Are Two Ways of This Type of Speciation They Are
If an error occurs during cell division known as autopolyploidy.
If there is more than one copy of chromosome or loss of a chromosome in one of the daughters and they are known as allopolyploidy.
Autopolyploidy: As an organism has two sets of chromosomes but due to certain abnormalities if the daughter cell has more than two sets of chromosomes then this condition is known as autopolyploidy.
Allopolyploidy: this type of speciation occurs when two different species mate and form new offspring. Example: tobacco, cotton, etc.
Difference Between Allopatric and Sympatric Speciation
Facts on Allopatric and Sympatric Speciation
1. Allopatric is speciation from a physical barrier.
2. In sympatric speciation, the 4n chromosome is formed instead of 2n.
3. In sympatric speciation, diploids cannot mate with tetraploids.
MCQ on Allopatric and Sympatric Speciation
1. Which of the Following Does Not Tend to Promote Speciation?
A) Founder Effect
B) Reproductive Isolation
C) Natural Selection
D) Gene Flow
Answer: (D)
2. Which of the Following Statements Explains Why Animals Are Less Likely Than Plants to Speciate by Polyploidy?
A) Animals have behavioural rituals that result in mate recognition.
B) Animal movement patterns ensure gene flow.
C) Animals rarely self-fertilize, so diploid gametes are much less likely to fuse.
D) Animal chromosomes are less likely to replicate incorrectly than plants.
Answer: (C)
3. The Two Key Factors Responsible for Speciation Among Populations Are
A) Mutation and heterozygote disadvantage
B) Reproductive isolation and genetic divergence
C) Postzygotic isolation and morphological change
D) Mutation and genetic drift
Answer: (B)
4. In Which Theory of Speciation Does a New Species Emerge from Within the Geographic Range of Its Ancestor?
A) Allopatric speciation
B) Parapatric speciation
C) Sympatric speciation
Answer: (A)
FAQs on Allopatric and Sympatric Speciation
1. What is speciation in the context of evolution?
Speciation is the evolutionary process by which new biological species arise. It is a fundamental concept in evolution because it is the primary mechanism that generates biodiversity. It occurs when a single ancestral population splits into two or more distinct populations that can no longer interbreed, leading to the formation of separate species.
2. What is allopatric speciation and what role does a geographical barrier play?
Allopatric speciation, also known as geographic speciation, occurs when a population is divided by a physical barrier such as a mountain range, river, or ocean. This geographical isolation prevents gene flow between the separated groups. Over time, each sub-population adapts to its unique environment through processes like natural selection and genetic drift, leading to genetic divergence. Eventually, they become so different that they are reproductively isolated and cannot interbreed even if the barrier is removed.
3. How does sympatric speciation occur without any geographical separation?
Sympatric speciation is the evolution of a new species from an ancestral species while both continue to inhabit the same geographical region. A physical barrier is absent. Instead, reproductive isolation arises from other factors within the shared habitat. Common mechanisms include:
- Polyploidy: An error in cell division results in offspring with extra sets of chromosomes (e.g., tetraploid from diploid parents), which can only breed with other polyploids. This is common in plants.
- Niche Differentiation: Subgroups within a population begin to exploit different resources or microhabitats, such as feeding on different types of food, which leads to them becoming reproductively isolated over time.
4. What are the key differences between allopatric and sympatric speciation?
The primary differences lie in the mechanism that initiates the divergence. Here are the key distinctions:
- Geographical Barrier: This is the defining feature of allopatric speciation, where a physical barrier splits a population. In sympatric speciation, there is no such barrier.
- Initial Driver: In allopatric speciation, the driver is physical separation. In sympatric speciation, the drivers are genetic (like polyploidy) or ecological (like niche partitioning).
- Gene Flow: Gene flow is stopped abruptly by the barrier in allopatric speciation. In sympatric speciation, gene flow is reduced within a population through intrinsic factors.
5. What are some classic examples of allopatric and sympatric speciation?
Real-world examples help illustrate these concepts clearly:
- Allopatric Speciation Example: The evolution of Darwin's finches on the Galápagos Islands is a classic case. An ancestral finch species colonised the islands, and geographical isolation on different islands led to the evolution of multiple distinct species, each with a beak adapted to its local food source.
- Sympatric Speciation Example: The apple maggot fly (Rhagoletis pomonella) in North America originally fed on hawthorn trees. When apple trees were introduced, a subgroup began to feed and mate exclusively on apples. This shift in host plant created reproductive isolation from the hawthorn-feeding flies, initiating sympatric speciation.
6. Why is speciation through polyploidy more common in plants than in animals?
Polyploidy is a much more successful mechanism for speciation in plants primarily because many plants can self-fertilise. An error during meiosis can produce a diploid (2n) gamete. If this gamete fuses with a normal haploid (n) gamete, it forms a sterile triploid. However, if it self-fertilises, it can create a viable tetraploid (4n) offspring. This new tetraploid plant is instantly reproductively isolated from the original diploid population but can reproduce with other tetraploids. In animals, self-fertilisation is rare, and their complex developmental pathways are often severely disrupted by changes in chromosome number, making polyploid offspring typically non-viable.
7. How does parapatric speciation differ from allopatric and sympatric speciation?
Parapatric speciation is considered an intermediate model between allopatric and sympatric speciation. In this mode, there is no specific physical barrier separating populations. Instead, the population is continuous over a large geographic area with varying environments. Individuals are more likely to mate with their neighbours than with individuals from distant parts of the range. This limited gene flow, combined with different selective pressures across the area, can cause populations to diverge. It differs from allopatric speciation because there is no hard barrier, and from sympatric speciation because the populations are not intermingling in the same location but are adjacent to each other.
