Allopatric-speciation

Speciation – Definition, Causes, Process, and Types of Speciation

Definition of Speciation

Speciation is the procedure of development of a new genetically independent group of organisms, called species, through the lapse of evolution.

The procedure of splitting of genetically homogenous population into two or more populations that undergo genetic differentiation and eventual reproductive isolation is called speciation.

The entire passage of evolution relies on the origin of new populations (types) that have higher adaptive efficiency than their forefathers.

Speciation occurs in two ways:

  • Change of old species into new species over time.
  • Dividing of a single species into many, is the multiplication of species.
Causes of Speciation
1.Geographic isolation

In the fruit fly example, some fruit fly larvae were washed up on an island, and speciation began since populations were prevented from interbreeding by geographical isolation. Researchers believe that geographic isolation is a common way for the process of speciation to start: rivers change course, mountains rise, continents drift, organisms migrate, and when a constant population is divided into two or smaller sized populations.

It doesn’t even need to be a physical barrier like a river that separates two or more groups of organisms– it might just be undesirable habitat between the two populations that prevents them from mating with one another.

Causes-of-Speciation

2. Natural selection

As discussed by Charles Darwin, different individuals in a species may establish particular distinct qualities which are useful and affect the genetic makeup of the individual. Under such conditions, these attributes will be conserved, and over time, new species might be formed.

However, in this case, the necessary element of this factor is that speciation happens only when a single species splits into a number of species leading to the multiplication of species.

3. Chromosomal Anomalies

Chromosomal mutations have the potential to serve as separating mechanisms, and the locking up and defense of an especially beneficial gene enhance through a chromosomal mutation. These mutations, when maintained from one generation to another, may lead to the formation of new species.

4. Reduction of gene flow

Nevertheless, speciation may likewise occur in a population without any particular extrinsic barrier to gene flow. Think of a circumstance in which a population crosses a broad geographic range, and breeding throughout the population is not random. Individuals in the far west would have no opportunity of mating with individuals in the far eastern end of the range. So, we have actually lowered gene flow, but not total isolation.

This may or may not sufficient to cause speciation. Speciation would also need different selective pressures at opposite ends of the variety, which would alter gene frequencies in groups at different ends of the variety so much that they would not have the ability to mate if they were reunited.

Reduction-of-gene-flow

 

Process of Speciation

Traditionally, speciation has been observed as a three-stage procedure:

  • Isolation of populations
  • Divergence in characteristics of separated populations (e.g. mating system or habitat use).
  • Reproductive isolation of populations that keeps isolation when populations enter into contact again (secondary contact).

The procedure of speciation begins with the isolation of the subpopulation of a species which might either take place through physical isolation (allotropic speciation) or hereditary isolation (sympatric speciation). When the population is separated, a gradual accumulation of little genetic modifications leads to a subpopulation of a type that eventually builds up many changes that the subpopulations become different species.

Over time, the subpopulation now ends up being genetically independent and will continue to diverge by mutation, selection, and genetic drift. Eventually, the genetic differentiation between the subpopulation ends up being so high that the formation of hybrids in between them would be physiologically, developmentally, or behaviourally impossible even if the modes of the separation were abolished.

Types of Speciation

The category of the modes or types of speciation is based on how much the geographical separation of the initial population contributes to the reduced gene flow and eventually, the formation of new species.

Speciation-types

1.Allopatric Speciation

Allopatric speciation is the mode of speciation in which the initial population is divided into two by a barrier resulting in reproductive seclusion.

The model for allopatric speciation was presented by Mayr. It is based on the principle that new species occur when some physical geographical barrier divides the big population of a species into two or more little populations. The individuals of these isolated populations can not interbreed because of their physical isolation.

Physical isolation may take place either due to physical barriers like vast stretches of ocean, high mountains, glaciers, deep river valleys, large rivers or deserts, or a substantial range due to a bigger geographical variety.

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Each separated population begins to adjust to their apart environments while collecting differences and developing independently into new species. Allopatric speciation can take place even in cases in which the barrier allows some individuals to cross the barrier to mate with the members of the other groups. For speciation even to be considered “allopatric,” gene circulation between the soon-to-be species needs to be significantly minimized– however it does not have to be totally lowered to absolutely zero.

Example of Allopatric speciation

The timeless example of allopatric speciation is that of Darwin’s finches. The divergent populations of finches living in the Galapagos Islands were observed to have differences in functions such as body size, color, and beak length or shape. The distinctions resulted because of the various kinds of food available in various Islands.

Allopatric-speciation

2.Sympatric Speciation

Sympatric speciation is the process of the development of new species from an original population that are not geographically separated.

It is based upon the establishment of new populations of a species in different environmental niches and the reproductive isolations of founders of the new population from the individuals of the source population.

Gene flow in between daughter and adult population throughout sympatric speciation is postulated to be inhibited by intrinsic aspects, such as chromosomal changes and non-random mating. Making use of a new niche might instantly reduce gene flow with individuals making use of a different niche. This mode of speciation prevails in herbivore insects when they begin feeding and mating on a new plant or when a new plant is presented within the geographical range of the species.

The gene flow is then reduced between the species that concentrate on a specific plant which may ultimately lead to the development of new species. The choice leading to expertise requires to be actually strong for the population to diverge. Thus, sympatric speciation is a sporadic event in multicellular organisms or arbitrarily mating populations.

Sympatric-Speciation-m

Example of Sympatric speciation

Sympatric speciation is observed in apple maggot flies which 200 years ago laid eggs and reproduced just on hawthorns and now lays eggs on both hawthorns and domestic apples. As a result, gene flow between parts of the population that mate on various kinds of fruit is reduced, and in fewer than 200 years, some hereditary differences between these two groups of flies have actually progressed.

3.Parapatric Speciation

Parapatric speciation is a highly uncommon case of speciation that occurs when a population is continually dispersed within a geographic area with no specific barriers to gene flow. Nonetheless, the population does not mate randomly within the population, however rather individuals’ mate more commonly with their closest geographical adjacent neighbors, resulting in irregular gene flow.

Non-random breeding might increase the rate of dimorphism within populations, in which differed morphological forms of the same species are displayed. The result of parapatric speciation is one or more distinct sub-populations (called ‘sister species’), which have little, continuous overlaps in their biogeographic range and are genotypically dimorphic.

Parapatric-Speciation

Example of Parapatric speciation

The grass specieAnthoxanthum odoratum where some species living near the mine have ended up being tolerant to heavy metals; nevertheless, other plants that do not live around the mines are not tolerant. But due to the fact that the plants are close together, they might fertilize each other and lead to new types.

Peripatric Speciation

Peripatric speciation is a type of allopatric speciation that takes place when populations that have ended up being isolated have very few individuals. Through this process, the population goes through a genetic bottleneck. Within the little sub-population, organisms which have the ability to make it through within the new environment might bring genes that were unusual within the main population but that triggers a small variation to behavior or morphology.

Through repeated mating, the frequency of these, when uncommon, genes boost within the small population. This is known as the ‘founder effect’. In time, the characteristic that was determined by the gene ends up being fixed within the population, resulting in a separated species that is evolutionarily distinct from the main population.

Peripatric-Speciation

Example of Peripatric speciation

The Australian bird Petroica multicolor and London Underground mosquito, a variation of the mosquito Culex pipiens, which entered the London Underground in the 19th century are examples of Peripatric speciation.

Multiple-Choice Questions (MCQ)

1. What is speciation?

  • a) A process of genetic isolation
  • b) The formation of new genetically independent groups of organisms
  • c) A type of mutation
  • d) Hybridization between species
  • Answer: b) The formation of new genetically independent groups of organisms

2. In speciation, what is the process of splitting a genetically homogenous population into two or more populations called?

  • a) Genetic drift
  • b) Reproductive isolation
  • c) Divergence
  • d) Allopatric speciation
  • Answer: d) Allopatric speciation

3. Which of the following is a cause of speciation related to physical barriers like mountains, rivers, or deserts?

  • a) Natural selection
  • b) Chromosomal anomalies
  • c) Reduction of gene flow
  • d) Geographic isolation
  • Answer: d) Geographic isolation

4. According to Charles Darwin, which process may lead to speciation when certain distinct traits are conserved and affect the genetic makeup of individuals?

  • a) Allopatric speciation
  • b) Natural selection
  • c) Chromosomal anomalies
  • d) Sympatric speciation
  • Answer: b) Natural selection
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5. How can chromosomal anomalies contribute to speciation?

  • a) By reducing gene flow
  • b) By enhancing gene flow
  • c) By causing physical barriers
  • d) By influencing natural selection
  • Answer: a) By reducing gene flow

6. In the process of speciation, what is the first stage traditionally observed?

  • a) Divergence
  • b) Reproductive isolation
  • c) Isolation of populations
  • d) Secondary contact
  • Answer: c) Isolation of populations

7. Which type of speciation involves the physical separation of populations into different geographic areas?

  • a) Sympatric speciation
  • b) Allopatric speciation
  • c) Parapatric speciation
  • d) Peripatric speciation
  • Answer: b) Allopatric speciation

8. What is the primary characteristic of allopatric speciation?

  • a) Continuous gene flow between populations
  • b) Geographical isolation
  • c) Non-random mating
  • d) Dimorphism within populations
  • Answer: b) Geographical isolation

9. Which example illustrates allopatric speciation?

  • a) Apple maggot flies on different fruits
  • b) Darwin’s finches on the Galapagos Islands
  • c) Australian birds adapting to heavy metals
  • d) London Underground mosquito variation
  • Answer: b) Darwin’s finches on the Galapagos Islands

10. What is sympatric speciation based on?

  • a) Geographic isolation
  • b) Chromosomal anomalies
  • c) Non-random mating
  • d) Different environmental niches
  • Answer: d) Different environmental niches

11. In sympatric speciation, what reduces gene flow between species within the same geographic area?

  • a) Chromosomal anomalies
  • b) Natural selection
  • c) Intrinsic factors
  • d) Physical barriers
  • Answer: c) Intrinsic factors

12. What is parapatric speciation characterized by?

  • a) Complete geographic isolation
  • b) Continuous gene flow
  • c) Dimorphism within populations
  • d) Limited overlap in biogeographic range
  • Answer: d) Limited overlap in biogeographic range

13. Which example illustrates parapatric speciation?

  • a) Australian birds adapting to heavy metals
  • b) Darwin’s finches on the Galapagos Islands
  • c) Grass species with variations near a mine
  • d) London Underground mosquito variation
  • Answer: c) Grass species with variations near a mine

14. What characterizes peripatric speciation?

  • a) Chromosomal mutations
  • b) High gene flow
  • c) Genetic bottleneck and founder effect
  • d) Continuous overlap in biogeographic range
  • Answer: c) Genetic bottleneck and founder effect

15. What is an example of peripatric speciation?

  • a) Apple maggot flies on different fruits
  • b) Australian birds adapting to heavy metals
  • c) Grass species with variations near a mine
  • d) London Underground mosquito variation
  • Answer: b) Australian birds adapting to heavy metals

16. What is the primary outcome of sympatric speciation?

  • a) Geographic isolation
  • b) Increased gene flow
  • c) Reproductive isolation
  • d) Continuous overlap in biogeographic range
  • Answer: c) Reproductive isolation

17. How does chromosomal anomalies contribute to speciation?

  • a) By reducing gene flow
  • b) By enhancing gene flow
  • c) By causing physical barriers
  • d) By influencing natural selection
  • Answer: a) By reducing gene flow

18. What is the role of geographic isolation in allopatric speciation?

  • a) Enhances gene flow
  • b) Reduces gene flow
  • c) Causes non-random mating
  • d) Promotes dimorphism within populations
  • Answer: b) Reduces gene flow

19. In which type of speciation might individuals mate more commonly with their closest geographical neighbors?

  • a) Allopatric speciation
  • b) Sympatric speciation
  • c) Parapatric speciation
  • d) Peripatric speciation
  • Answer: c) Parapatric speciation

20. What initiates the process of speciation through the lapse of evolution?

  • a) Reduction of gene flow
  • b) The formation of new genetically independent groups
  • c) Dimorphism within populations
  • d) Continuous overlap in biogeographic range
  • Answer: b) The formation of new genetically independent groups

21. Which type of speciation involves populations with very few individuals and a genetic bottleneck?

  • a) Allopatric speciation
  • b) Sympatric speciation
  • c) Parapatric speciation
  • d) Peripatric speciation
  • Answer: d) Peripatric speciation

 

FAQs about Speciation:

1. What is speciation?

  • Speciation is the process of the development of a new genetically independent group of organisms, called species, through the lapse of evolution.

2. How does speciation occur?

  • Speciation occurs through the splitting of a genetically homogenous population into two or more populations that undergo genetic differentiation and eventual reproductive isolation.

3. In how many ways does speciation occur?

  • Speciation occurs in two ways: the change of old species into new species over time and the dividing of a single species into many, leading to the multiplication of species.

4. What are the causes of speciation?

  • The causes of speciation include geographic isolation, natural selection, chromosomal anomalies, and reduction of gene flow.

5. How does geographic isolation contribute to speciation?

  • Geographic isolation occurs when a physical barrier divides a population, preventing interbreeding. This separation initiates genetic differentiation, leading to the formation of new species.

6. How does natural selection lead to speciation?

  • Natural selection results in the development and conservation of specific traits that influence the genetic makeup of individuals, eventually leading to the multiplication of species.

7. What role do chromosomal anomalies play in speciation?

  • Chromosomal anomalies serve as separating mechanisms, enhancing the defense of beneficial genes. These mutations, when maintained, may lead to the formation of new species.

8. How does the reduction of gene flow contribute to speciation?

  • Reduction of gene flow occurs when populations are not randomly mating across a broad geographic range, leading to isolated groups with altered gene frequencies and, potentially, new species.
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9. What is the traditional process of speciation?

  • Traditionally, speciation is observed as a three-stage process: isolation of populations, divergence in characteristics of separated populations, and reproductive isolation maintaining separation upon secondary contact.

10. What are the types of speciation?

  • The main types of speciation include allopatric speciation, sympatric speciation, parapatric speciation, and peripatric speciation.

11. What is allopatric speciation?

  • Allopatric speciation occurs when the initial population is divided into two by a physical barrier, resulting in reproductive isolation.

12. Can allopatric speciation occur with some gene flow between populations?

  • Yes, allopatric speciation can occur even if some individuals cross the barrier for mating, as long as gene flow is significantly reduced.

13. What is sympatric speciation?

  • Sympatric speciation is the process of developing new species from an original population without geographic separation.

14. How does parapatric speciation occur?

  • Parapatric speciation occurs when a population is continuously dispersed within a geographic area, but individuals mate more commonly with their closest geographical neighbors, leading to irregular gene flow.

15. What is peripatric speciation?

  • Peripatric speciation is a type of allopatric speciation that occurs when isolated populations have very few individuals, resulting in a genetic bottleneck and the evolution of a separated species.

 

Summarizing Speciation

The tutorial on speciation covers the definition, causes, processes, and types of speciation. Speciation is the evolutionary process resulting in the development of genetically independent groups of organisms, known as species. This occurs through the splitting of a homogenous population into new populations with increased adaptive efficiency. There are two primary ways speciation occurs: the gradual change of old species into new ones over time and the multiplication of species by dividing a single species.

The causes of speciation include geographic isolation, natural selection, chromosomal anomalies, and the reduction of gene flow. Geographic isolation, where populations are separated by physical barriers, is a common initiator of speciation. Natural selection, as proposed by Darwin, leads to the development and conservation of distinct traits, resulting in the formation of new species. Chromosomal anomalies, such as mutations, can serve as separating mechanisms, and the reduction of gene flow occurs when populations no longer mate randomly.

The process of speciation traditionally involves three stages: isolation of populations, divergence in characteristics of separated populations, and reproductive isolation maintaining separation upon secondary contact. The subpopulation of a species becomes genetically independent through gradual genetic changes, leading to the development of new species over time.

There are different types of speciation, including allopatric speciation (physical barrier-induced isolation), sympatric speciation (development of new species without geographic separation), parapatric speciation (geographically adjacent populations with irregular gene flow), and peripatric speciation (isolated populations with few individuals).

Examples such as Darwin’s finches illustrate allopatric speciation, while apple maggot flies demonstrate sympatric speciation. Parapatric speciation is observed in grass species near mines, and peripatric speciation is exemplified by the Australian bird Petroica multicolor and the London Underground mosquito.

In conclusion, speciation is a dynamic process influenced by various factors, resulting in the diversity of life forms over time.