Difference Between Allopatric and Sympatric Speciation

Main Difference – Allopatric vs Sympatric Speciation

Allopatric speciation and sympatric speciation are the two major mechanisms involved in the formation of new species from a pre-existing species. The process of forming new species from a pre-existing species is called anagenesis. Anagenesis occurs through reproductive isolation of individuals in a population. The main difference between allopatric speciation and sympatric speciation is that allopatric speciation occurs when a biological population is isolated by an extrinsic barrier causing a genetic reproductive isolation of individuals whereas sympatric speciation occurs when new, distinct species are evolved due to polyploidy.

Key Areas Covered

1. What is Allopatric Speciation
      – Definition, Features, Examples
2. What is Sympatric Speciation
      – Definition, Types, Features, Examples
3. What are the Similarities Between Allopatric and Sympatric Speciation
      – Outline of Common Features
4. What is the Difference Between Allopatric and Sympatric Speciation
      – Comparison of Key Differences

Kay Terms: Allopatric Speciation, Allopolyploid Speciation, Anagenesis, Autopolyploid Speciation, Extrinsic Barriers, Parapatric Speciation, Peripatric Speciation, Polyploidy, Reproductive Isolation, Sympatric Speciation

What is Allopatric Speciation

Allopatric speciation refers to the emergence of a new species when a population is geographically isolated from its ancestor. Allopatric speciation is the most common type of speciation. A particular population may be geographically separated due to extrinsic barriers such as land topography occurred by earthquakes, deserts, mountains, swamps, and ice fields. Once a population is geographically separated into two, the gene flow ceases between the two. Then, each population becomes genetically different due to the different selective pressures of the two environments they live. After separation, small populations may contain different allele frequencies since they undergo founder effect. Thus, natural selection and genetic drift act differently upon the two populations.

Difference Between Allopatric and Sympatric Speciation

Figure 1: Allopatric speciation

Ultimately, two different genetic backgrounds emerge, raising new species which are incapable of interbreeding. The greater the distance of the separation, the greater differentiation of the two species will occur. Darwin’s finches and the squirrels in the Grand Canyon are the examples of allopatric speciation. Allopatric speciation is shown in figure 1.

What is Sympatric Speciation

The speciation which occurs when the individuals in the same habitat are reproductively isolated from each other is referred to as sympatric speciation. Sympatric speciation mostly occurs through polyploidy. When an offspring inherits more than the normal chromosome number in the population, this offspring is incapable of reproducing with individuals who contain the normal chromosome number of the population. This creates the reproductive isolation within the same population. Sympatric speciation mostly occurs in plants and is rare in animals. Since plants are capable of self-reproducing, the polyploid offspring can produce a new, distinct generation by themselves. The two types of sympatric speciation are allopolyploid speciation and autopolyploid speciation.

Main Difference - Allopatric vs Sympatric Speciation

Figure 2: Sympatric Speciation

Allopolyploid Speciation

The hybridization of two different species will produce a third species in allopolyploid speciation. The third species is incapable of interbreeding with the two original species. Most of the times, the two parent species are different from each other by their chromosome number. Wheat and Arabidopsis plants are the examples of allopolyploid speciation.

Autopolyploid Speciation

In autopolyploid speciation, a new species is produced by doubling the chromosome number in the original population. Since the offspring is composed of doubled chromosome number, it is incapable of interbreeding with the original species. Potatoes are an example of autopolyploid speciation. The sympatric speciation is shown in figure 2.

Similarities Between Allopatric and Sympatric Speciation

Both allopatric and sympatric speciation occurs through the reproductive isolation of individuals in a population.
Both processes are involved in evolving new, distinct species from the pre-existing species.
The new species is incapable of interbreeding with the pre-existing species.

Definition

Allopatric Speciation: Allopatric speciation is the physical isolation of a biological population by an extrinsic barrier, evolving an intrinsic reproductive isolation.

Sympatric Speciation: Sympatric speciation is the evolution of new species from a single ancestral species while living in the same habitat.

Geographic Isolation

Allopatric Speciation: Allopatric speciation takes place through geographic isolation.

Sympatric Speciation: Geographic isolation is not required for sympatric speciation.

Major Differentiation Mechanism

Allopatric Speciation: The major differentiation mechanism of allopatric speciation is natural selection.

Sympatric Speciation: The major differentiation mechanism of sympatric speciation is polyploidy.

Speed of Emerging New Species

Allopatric Speciation: The speed of the emergence of new species is slow in allopatric speciation.

Sympatric Speciation: The speed of the emerge of new species is fast with autopolyploidy and slow with allopolyploidy.

Frequency

Allopatric Speciation: Allopatric speciation is common in nature.

Sympatric Speciation: Sympatric speciation is common in plants.

Examples

Allopatric Speciation: Darwin’s finches and squirrels in the Grand Canyon are some examples of allopatric speciation.

Sympatric Speciation: The cultivated wheat, corn, and tobacco and the African tilapia are some examples of sympatric speciation.

Conclusion

Allopatric speciation and sympatric speciation are the two major mechanisms of speciation. Both allopatric and sympatric speciation occur due to the reproductive isolation of individuals in the same species. In allopatric speciation, geographical barriers serve as a physical barrier for the interbreeding within the individuals of a population. In sympatric speciation, genetic incompatibilities serve as the reproductive barrier. Hence, the individuals within the same population are changed into two species independently. The main difference between allopatric and sympatric speciation is the type of barriers involved in the reproductive isolation in each mechanism.

Reference:

1. “Allopatric speciation.” Evolution – A-Z . Blackwell Publishing, n.d. Web. Available here. 20 July 2017.
2. “Sympatric Speciation.” Boundless. N.p., 26 May 2016. Web. Available here. 21 July 2017.

Image Courtesy:

1. “Allopatric Speciation (Process diagram)” By Andrew Z. Colvin – Own work (CC BY-SA 4.0) via Commons Wikimedia