Difference Between Allopatric and Sympatric Speciation

Allopatric vs Sympatric Speciation

The world is an ever-changing place, and it demands the species to adapt to new conditions every day. The extant species will have to take the challenge by adapting through changing the genetic composition in order to survive.

When the genetic compositions change, new species are formed, which is called the speciation. As in a slogan by the Roman poet Horace “dulce et decorum est pro patria mori” that means strong and proper ones die for their homeland, which is further described as they rather live than dying.

However, the relationship of allopatric to sympatric speciation to Horace’s slogan is interesting. The word “patria” was used to describe the homeland, and it provided the suffix to form the words “allopatric” and “sympatric.” That envisages these terms are related with some geographical sense.

What is Allopatric Speciation?

Allopatric speciation is also known as the geographic speciation where one species becomes two due to the formation of geographical barriers such as land separation, mountain formation, or emigration. When a geographical barrier is formed, isolation of one portion of a particular population occurs.

Then, there may be differences in environmental and ecological conditions that the two portions have to face, and genetic modifications will take place. With time, those genetic modifications will cause adequate changes to create a new species from the original one.

This process could be speeded up when mutations take place due to geographical isolation. Adaptive radiation is one of the consequences of allopatric speciation, where one species becomes adapted to different environmental demands in different places.

However, the dispersion of populations could be identified as one of the causes for the geographical isolation of species that leads to form new species through allopatric speciation.

What is Sympatric Speciation?

Sympatric speciation is the formation of new species where the genetic modification has been based on a single ancestor. As the term sympatric implies, the geographic range is the same for both the new and former species.

Genetic polymorphism, which means the actively and steadily maintained population, is important to consider in understanding the mechanism of sympatric speciation.

Genetically distinct populations with individuals who are naturally selected through mating preferences have been isolated and formed a new subgroup inside a species.

This subgroup will have a different gene pool, which will have enough distinction to prove that they belong to a new species. One of the most respected theories to explain the mechanism of sympatric speciation is the Disruptive Selection Model proposed by John Maynard Smith in 1966. 

According to the model, homozygous individuals are more favoured than the heterozygous individuals, especially where the incomplete dominance has an effect.

That causes a species to be diverted into two surviving groups with one group having the homozygous dominant genotype and the other with the homozygous recessive, but the heterozygous ones are eradicated. The two homozygous groups will form two separate species with time.

What is the difference between Allopatric Speciation and Sympatric Speciation?

  • Allopatric speciation takes place in different geographic regions but not the sympatric speciation.
  • Allopatric is the commonest mechanism of forming new species compared to sympatric mechanism.
  • Geographical isolation or divergence has to take place in allopatric speciation, but the driving force for the formation of new species in sympatric speciation is the genetic or sexual isolation.

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