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7.10 Speciation

6 min readjanuary 13, 2023

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Sexual Reproduction

is the process by which new species evolve from existing ones. There are several mechanisms by which can occur, but one of the most common is through the process of . This occurs when two populations of a species become physically or biologically separated from each other, such that they can no longer and exchange genetic information. Over time, these isolated populations may evolve in different ways, leading to the development of new species. 😁

The , which defines a species as a group of organisms capable of interbreeding and producing viable, fertile offspring, is one of the most widely accepted definitions of species. This concept is based on the idea that species are reproductively isolated from one another, and that this isolation is the primary mechanism by which new species evolve.

To sum the last two paragraphs in two sentences: species are defined by their ability to sexually reproduce with one another. In order for to be considered “valid,” they need to be able to by exchanging genetic information for a viable, fertile offspring.

Different Species?

For example, a and a can breed and create a , but that cannot breed with another to continue its own lineage, which is why donkeys and horses are considered to be separate species. (Additionally, they have different numbers of chromosomes as well). When two animals can no longer breed with one another, they are classified as different species. 🐎

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fdonkey-1268897_1280.jpg?alt=media&token=2bcfa86b-92d5-41b3-8a14-aef977db9120

Image courtesy of Pixabay.

Rates of Evolution

The rate of and may also differ under different ecological conditions. For instance, and are two different, well-known models that describe the pace of . 🦋

Punctuated equilibrium is a theory proposed by and in the 1970s. It suggests that occurs in fits and starts, with long periods of stasis (little or no change) punctuated by brief periods of rapid . This theory suggests that is not a slow, steady process, but instead occurs in bursts, with most species remaining relatively unchanged for most of their history.

On the other hand, is a model that proposes that is a slow, steady process that occurs over hundreds of thousands or millions of years. This model suggests that is a gradual accumulation of small changes over time, leading to the gradual development of new species.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-0AYuBtKkSkns.jpg?alt=media&token=8fd12b1f-cffb-4550-9456-636c957365e7

Source: Biology Dictionary

What if We Isolate Different Populations?

is a type of that occurs when different populations of a species adapt to different habitats, leading to the development of new forms. This can happen when a population becomes geographically isolated and is exposed to different selective pressures. As a result, the isolated population may evolve different characteristics that allow them to better survive and reproduce in their new habitat. 🐺

rates can be especially rapid during times of , which is when a lineage diversifies into many new forms as it adapts to different habitats and ecological niches. This can happen when new habitats become available, such as when a volcano creates a new island, or when a mass extinction event opens up new ecological niches. During these times, the rate of can be much higher than during times of stasis, as new forms evolve to fill the available niches.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-hy2ebZfgf986.jpg?alt=media&token=f37cb2bc-8bbb-4332-b866-ed6c1bdcd47c

Source: VectorMine

Types of Speciation

Allopatric Speciation

occurs when two populations become “reproductively isolated” from one another. For example, this could happen if there is a geographical barrier separating individuals of the species. If they cannot continue to breed with each other, it is possible that the two separate populations will evolve separately until they are unable to breed with each other. This is called .

Sympatric Speciation

Another way that could happen is through . This is when individuals within the same geographic area are influenced by either or mating preferences. occurs when two opposing traits are equally favored by nature. As the population begins to evolve oppositely, is likely to occur.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-zxqHqlbMr1dN.jpeg?alt=media&token=dda07a40-0953-45e4-9a0a-743c3d62b22e

Source: BioNinja

Prezygotic vs. Postzygotic Isolation

These instances can be categorized as either prezygotic or . prevents the fertilization of eggs when two individuals breed, thus making it impossible to reproduce. This would be present in examples such as , or any other outside forces preventing mating or fertilization. does not allow the formation of a fertile offspring, like in the example). 🥚

Practice Problem

In a hypothetical scenario, a population of birds living on a remote island becomes separated from the mainland population by a newly formed oceanic trench. Over time, the isolated island population evolves distinct physical and behavioral characteristics that allow them to better survive on the island. Meanwhile, the mainland population continues to evolve in response to different selective pressures. 🐦

Using specific examples from the scenario, identify the type of that has occurred in the island bird population and explain the mechanism behind it. Then, explain the type of barrier (prezygotic or postzygotic) that is preventing interbreeding between the island and mainland bird populations.

In your answer, be sure to include specific examples of the physical and behavioral differences between the island and mainland bird populations, and explain how these differences would affect their ability to . Also, be sure to discuss the role of , , and in the process, and how the formation of the oceanic trench may have influenced these factors.

Your answer should be detailed, clear, and well-supported by evidence from the scenario, as well as from current scientific understanding of and .

Answer

The type of that has occurred in this scenario is likely . This is because the island population of birds has become physically separated from the mainland population by the formation of the oceanic trench, which is the barrier that prevents interbreeding between the two populations. As a result of this isolation, the island population has been exposed to different selective pressures than the mainland population.

Over time, these differences have led to the development of distinct physical and behavioral characteristics that allows the island birds to survive better in their specific environment, while the mainland population continues to evolve in response to different selective pressures.

The barrier preventing interbreeding between the island and mainland bird populations is a prezygotic barrier. This is because the physical and behavioral differences that have evolved in the island population would prevent successful mating and fertilization from occurring between the two populations even if they were to come into contact. For example, the island birds may have developed larger beaks to crack open harder seeds found on the island, while the mainland birds may have evolved a different diet and smaller beaks.

The differences in their beak size and shape would make it physically impossible for the birds to mate and produce viable offspring. Additionally, the island birds may have developed a different courtship ritual or mating call that the mainland birds would not respond to, further preventing successful breeding between the two populations.

In conclusion, the island bird population has undergone as a result of physical isolation caused by the formation of oceanic trench, which has led to the development of physical and behavioral characteristics that are specific to the island environment. The barrier preventing interbreeding between the island and mainland bird populations is prezygotic, as the physical and behavioral differences would prevent successful mating and fertilization from occurring between the two populations.

Key Terms to Review (24)

Reproductive Isolation

: Reproductive isolation occurs when different species are unable to interbreed and produce viable offspring due to physical, behavioral, or genetic barriers.

Sexual Reproduction

: Sexual reproduction is a type of reproduction where two parents contribute genetic material to produce offspring that are genetically different from either parent.

Speciation

: Speciation is an evolutionary process by which populations evolve to become distinct species.

Interbreed

: Interbreeding refers to when members of the same species mate and produce offspring.

Biological Species Concept

: The Biological Species Concept (BSC) is a way of defining species as groups of interbreeding natural populations that are reproductively isolated from other such groups.

Donkey

: A donkey is a domesticated hoofed mammal belonging to the horse family and used as a work animal or for riding.

Horse

: A horse is a large domesticated mammal of the family Equidae and the genus Equus. It's known for its speed, strength, and ability to be trained for various tasks.

Mule

: A mule is an animal that results from breeding between a male donkey (jack) and a female horse (mare). Mules inherit desirable qualities from both parents; they're hardy like donkeys but larger and faster like horses.

Evolution

: Evolution is the process by which species change over time through variations in their genetic material. These changes may lead to new species and greater biodiversity.

Punctuated Equilibrium

: Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and rapid events of branching speciation.

Niles Eldredge

: Niles Eldredge is an American biologist and paleontologist who collaborated with Stephen Jay Gould to develop the theory of punctuated equilibrium.

Stephen Jay Gould

: Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science who contributed significantly to the field of evolutionary biology by developing, along with Niles Eldredge, the theory of punctuated equilibrium.

Divergent Evolution

: Divergent evolution refers to the process whereby groups from the same common ancestor evolve and accumulate differences, resulting in the formation of new species.

Gradualism

: Gradualism is a theory in biology that suggests evolution occurs slowly and steadily over a long period of time, with small genetic changes accumulating to bring about large changes.

Adaptive Radiation

: Adaptive radiation is an evolutionary process where organisms rapidly diversify into multiple new forms especially when environmental conditions change creating new opportunities (niches).

Allopatric Speciation

: Allopatric speciation is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with genetic interchange.

Sympatric Speciation

: Sympatric speciation is the process through which new species evolve from a single ancestral species while inhabiting the same geographic region.

Disruptive Selection

: Disruptive selection is a type of natural selection that simultaneously favors individuals at both extremes of the distribution.

Prezygotic Isolation

: Prezygotic isolation is a mechanism that prevents different species from interbreeding and producing hybrid offspring. This occurs before the fertilization of eggs.

Postzygotic Isolation

: Postzygotic isolation refers to mechanisms that prevent successful development and reproduction after fertilization has occurred between members of different species.

Habitat Isolation

: Habitat isolation is a type of prezygotic barrier where two closely related species do not mate because they inhabit different environments within the same geographic area.

Genetic Drift

: Genetic drift is a mechanism of evolution that causes random changes in the frequency of alleles (versions of a gene) in a population over time.

Mutation

: A mutation is any change that occurs in the DNA sequence. It can lead to variations within species and potentially new species altogether.

Natural Selection

: Natural selection is an evolutionary process where organisms best adapted to their environment tend to survive and pass on their genetic traits to succeeding generations.

7.10 Speciation

6 min readjanuary 13, 2023

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Sexual Reproduction

is the process by which new species evolve from existing ones. There are several mechanisms by which can occur, but one of the most common is through the process of . This occurs when two populations of a species become physically or biologically separated from each other, such that they can no longer and exchange genetic information. Over time, these isolated populations may evolve in different ways, leading to the development of new species. 😁

The , which defines a species as a group of organisms capable of interbreeding and producing viable, fertile offspring, is one of the most widely accepted definitions of species. This concept is based on the idea that species are reproductively isolated from one another, and that this isolation is the primary mechanism by which new species evolve.

To sum the last two paragraphs in two sentences: species are defined by their ability to sexually reproduce with one another. In order for to be considered “valid,” they need to be able to by exchanging genetic information for a viable, fertile offspring.

Different Species?

For example, a and a can breed and create a , but that cannot breed with another to continue its own lineage, which is why donkeys and horses are considered to be separate species. (Additionally, they have different numbers of chromosomes as well). When two animals can no longer breed with one another, they are classified as different species. 🐎

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fdonkey-1268897_1280.jpg?alt=media&token=2bcfa86b-92d5-41b3-8a14-aef977db9120

Image courtesy of Pixabay.

Rates of Evolution

The rate of and may also differ under different ecological conditions. For instance, and are two different, well-known models that describe the pace of . 🦋

Punctuated equilibrium is a theory proposed by and in the 1970s. It suggests that occurs in fits and starts, with long periods of stasis (little or no change) punctuated by brief periods of rapid . This theory suggests that is not a slow, steady process, but instead occurs in bursts, with most species remaining relatively unchanged for most of their history.

On the other hand, is a model that proposes that is a slow, steady process that occurs over hundreds of thousands or millions of years. This model suggests that is a gradual accumulation of small changes over time, leading to the gradual development of new species.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-0AYuBtKkSkns.jpg?alt=media&token=8fd12b1f-cffb-4550-9456-636c957365e7

Source: Biology Dictionary

What if We Isolate Different Populations?

is a type of that occurs when different populations of a species adapt to different habitats, leading to the development of new forms. This can happen when a population becomes geographically isolated and is exposed to different selective pressures. As a result, the isolated population may evolve different characteristics that allow them to better survive and reproduce in their new habitat. 🐺

rates can be especially rapid during times of , which is when a lineage diversifies into many new forms as it adapts to different habitats and ecological niches. This can happen when new habitats become available, such as when a volcano creates a new island, or when a mass extinction event opens up new ecological niches. During these times, the rate of can be much higher than during times of stasis, as new forms evolve to fill the available niches.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-hy2ebZfgf986.jpg?alt=media&token=f37cb2bc-8bbb-4332-b866-ed6c1bdcd47c

Source: VectorMine

Types of Speciation

Allopatric Speciation

occurs when two populations become “reproductively isolated” from one another. For example, this could happen if there is a geographical barrier separating individuals of the species. If they cannot continue to breed with each other, it is possible that the two separate populations will evolve separately until they are unable to breed with each other. This is called .

Sympatric Speciation

Another way that could happen is through . This is when individuals within the same geographic area are influenced by either or mating preferences. occurs when two opposing traits are equally favored by nature. As the population begins to evolve oppositely, is likely to occur.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-zxqHqlbMr1dN.jpeg?alt=media&token=dda07a40-0953-45e4-9a0a-743c3d62b22e

Source: BioNinja

Prezygotic vs. Postzygotic Isolation

These instances can be categorized as either prezygotic or . prevents the fertilization of eggs when two individuals breed, thus making it impossible to reproduce. This would be present in examples such as , or any other outside forces preventing mating or fertilization. does not allow the formation of a fertile offspring, like in the example). 🥚

Practice Problem

In a hypothetical scenario, a population of birds living on a remote island becomes separated from the mainland population by a newly formed oceanic trench. Over time, the isolated island population evolves distinct physical and behavioral characteristics that allow them to better survive on the island. Meanwhile, the mainland population continues to evolve in response to different selective pressures. 🐦

Using specific examples from the scenario, identify the type of that has occurred in the island bird population and explain the mechanism behind it. Then, explain the type of barrier (prezygotic or postzygotic) that is preventing interbreeding between the island and mainland bird populations.

In your answer, be sure to include specific examples of the physical and behavioral differences between the island and mainland bird populations, and explain how these differences would affect their ability to . Also, be sure to discuss the role of , , and in the process, and how the formation of the oceanic trench may have influenced these factors.

Your answer should be detailed, clear, and well-supported by evidence from the scenario, as well as from current scientific understanding of and .

Answer

The type of that has occurred in this scenario is likely . This is because the island population of birds has become physically separated from the mainland population by the formation of the oceanic trench, which is the barrier that prevents interbreeding between the two populations. As a result of this isolation, the island population has been exposed to different selective pressures than the mainland population.

Over time, these differences have led to the development of distinct physical and behavioral characteristics that allows the island birds to survive better in their specific environment, while the mainland population continues to evolve in response to different selective pressures.

The barrier preventing interbreeding between the island and mainland bird populations is a prezygotic barrier. This is because the physical and behavioral differences that have evolved in the island population would prevent successful mating and fertilization from occurring between the two populations even if they were to come into contact. For example, the island birds may have developed larger beaks to crack open harder seeds found on the island, while the mainland birds may have evolved a different diet and smaller beaks.

The differences in their beak size and shape would make it physically impossible for the birds to mate and produce viable offspring. Additionally, the island birds may have developed a different courtship ritual or mating call that the mainland birds would not respond to, further preventing successful breeding between the two populations.

In conclusion, the island bird population has undergone as a result of physical isolation caused by the formation of oceanic trench, which has led to the development of physical and behavioral characteristics that are specific to the island environment. The barrier preventing interbreeding between the island and mainland bird populations is prezygotic, as the physical and behavioral differences would prevent successful mating and fertilization from occurring between the two populations.

Key Terms to Review (24)

Reproductive Isolation

: Reproductive isolation occurs when different species are unable to interbreed and produce viable offspring due to physical, behavioral, or genetic barriers.

Sexual Reproduction

: Sexual reproduction is a type of reproduction where two parents contribute genetic material to produce offspring that are genetically different from either parent.

Speciation

: Speciation is an evolutionary process by which populations evolve to become distinct species.

Interbreed

: Interbreeding refers to when members of the same species mate and produce offspring.

Biological Species Concept

: The Biological Species Concept (BSC) is a way of defining species as groups of interbreeding natural populations that are reproductively isolated from other such groups.

Donkey

: A donkey is a domesticated hoofed mammal belonging to the horse family and used as a work animal or for riding.

Horse

: A horse is a large domesticated mammal of the family Equidae and the genus Equus. It's known for its speed, strength, and ability to be trained for various tasks.

Mule

: A mule is an animal that results from breeding between a male donkey (jack) and a female horse (mare). Mules inherit desirable qualities from both parents; they're hardy like donkeys but larger and faster like horses.

Evolution

: Evolution is the process by which species change over time through variations in their genetic material. These changes may lead to new species and greater biodiversity.

Punctuated Equilibrium

: Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and rapid events of branching speciation.

Niles Eldredge

: Niles Eldredge is an American biologist and paleontologist who collaborated with Stephen Jay Gould to develop the theory of punctuated equilibrium.

Stephen Jay Gould

: Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science who contributed significantly to the field of evolutionary biology by developing, along with Niles Eldredge, the theory of punctuated equilibrium.

Divergent Evolution

: Divergent evolution refers to the process whereby groups from the same common ancestor evolve and accumulate differences, resulting in the formation of new species.

Gradualism

: Gradualism is a theory in biology that suggests evolution occurs slowly and steadily over a long period of time, with small genetic changes accumulating to bring about large changes.

Adaptive Radiation

: Adaptive radiation is an evolutionary process where organisms rapidly diversify into multiple new forms especially when environmental conditions change creating new opportunities (niches).

Allopatric Speciation

: Allopatric speciation is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with genetic interchange.

Sympatric Speciation

: Sympatric speciation is the process through which new species evolve from a single ancestral species while inhabiting the same geographic region.

Disruptive Selection

: Disruptive selection is a type of natural selection that simultaneously favors individuals at both extremes of the distribution.

Prezygotic Isolation

: Prezygotic isolation is a mechanism that prevents different species from interbreeding and producing hybrid offspring. This occurs before the fertilization of eggs.

Postzygotic Isolation

: Postzygotic isolation refers to mechanisms that prevent successful development and reproduction after fertilization has occurred between members of different species.

Habitat Isolation

: Habitat isolation is a type of prezygotic barrier where two closely related species do not mate because they inhabit different environments within the same geographic area.

Genetic Drift

: Genetic drift is a mechanism of evolution that causes random changes in the frequency of alleles (versions of a gene) in a population over time.

Mutation

: A mutation is any change that occurs in the DNA sequence. It can lead to variations within species and potentially new species altogether.

Natural Selection

: Natural selection is an evolutionary process where organisms best adapted to their environment tend to survive and pass on their genetic traits to succeeding generations.