4.6 Lesson (Sem) - Speciation

​Lesson - Speciation

• Do you think these lizards will mate together? Why or why not?

• Are these lizards different species?​

​Adaptations

Macroevolution

• large-scale changes above the species level (new groups, extinctions) over a long time

• built from many microevolution steps → natural selection and genetic drift change allele frequencies

• ​​Microevolution is a change in allele frequencies in a population’s gene pool across generations gene pool → natural selection and genetic drift

• Populations evolve, NOT individuals.

​

​Macroevolution refers to large-scale changes above the species level over a ______________ time.

Species: a group that can naturally interbreed and produce fertile offspring.

• Population

  • group of the same species living in the same place at the same time

• Horse (2n=64) × donkey (2n=62) → hybrid with 63 chromosomes, disrupting meiosis.

• Males are sterile; females are almost always sterile, with rare fertile females.

• Mule = male donkey (jack) × female horse (mare).

• Hinny = male horse (stallion) × female donkey (jenny).

A species is a group of organisms that can ___________ and produce ___________.

Speciation is the process by which populations become reproductively isolated and form a new species

• as their gene pools diverge due to natural selection and genetic drift.

​​Speciation is the process of forming a brand new species.
CAN'T BREED → NEW SPECIES

https://youtu.be/rdZOwyDbyL0?feature=shared&t=75

​Reproductive Isolation

​The Process of Speciation
1. Isolation → stops gene flow

• When gene flow (movement of alleles between groups) is reduced or cut off, differences build up.

• Barrier like a river, a mountain...

• Mechanically impossible to mate

• Different mating times

• Different mating rituals

2. Divergence over time

• As separated populations live in different environments, they adapt differently over time due to natural selection favoring different traits in different environments and genetic drift (chance events).

3. Reproductive isolation:

• Long-term geographic separation can lead to reproductive isolation.

• If two populations no longer interbreed, speciation has occurred.

​Which of the following describes the first step in the process of speciation?
a. Divergence
b. Reproductive isolation
c. Isolation (stopping gene flow)
d. Formation of a sterile hybrid

Multiple Choice

New species develop when

• populations become reproductively isolated and can no longer interbreed successfully

• individuals in a population choose different foods for a short time

• members of the same population all migrate to a new habitat together

• organisms within one species temporarily change behavior during one season

​Allopatric Speciation

• a physical barrier splits a population; no mating across the barrier; canyons, mountains, rivers, islands, glaciers.

  • Why it works: barrier stops gene flow, then selection + drift drive divergence.

• AKA Geographic Isolation

​Allopatric speciation occurs when a physical ________________ splits a population, stopping gene flow.

​The Kaibab squirrel and the Abert's squirrel live on opposite sides of the Grand Canyon and are believed to have evolved from a common ancestor. This is an example of:
a. Sympatric speciation
b. Allopatric speciation
c. Temporal isolation
d. Behavioral isolation

Sympatric Speciation

• no physical barrier

• isolation happens by behavior, timing, habitat, mechanics, or genetics.

Prezygotic Barriers

• BEFORE fertilization

• Geographic Isolation

• Behavioral Isolation

• Temporal Isolation

• Gametic Isolation

• Habitat Isolation

• Mechanical Isolation

Postyzygotic Barriers

• AFTER fertilization

• Reduced hybrid viability

• Reduced hybrid fertility

• Hybrid breakdown

TYPES OF REPRODUCTIVE ISOLATION

Geographic Isolation = Allopatric Speciation

• an event creates a physical barrier that divides a population into two or more separate groups

• canyons, mountains, rivers, islands, glaciers.

• Why it works: barrier stops gene flow, then selection + drift drive divergence.

• Ex: Grand Canyon squirrels (Abert’s vs. Kaibab).

• Ex: Island colonization → many species over time (e.g., finches, anoles).

Multiple Choice

A single population of salamanders is separated by the formation of a wide, dry valley. For thousands of years, the two groups evolve in isolation. When a researcher brings them together, they find the salamanders can no longer interbreed. This is a clear example of:

• Speciation caused by geographic isolation.

• Speciation caused by temporal isolation.

• Convergent evolution due to similar predators.

• A population bottleneck with no resulting evolution.

Behavioral isolation:

• different signals/courtship (songs, dances, light flashes) → no mating.

​​The Eastern and Western Meadowlark developed different courtship songs and no longer interbreed.

​In behavioral isolation, different mating signals or ________________ prevent two groups from interbreeding.

Multiple Choice

The northern spotted owl is a medium-sized, dark brown owl, while the Mexican spotted owl is brown with irregular white and brown spots. The female Mexican spotted owls prefer mating with male Mexican spotted owls though they can mate with the northern spotted owls. A scientist finds that the two species of spotted owls were once the same species.

What kind of isolation has caused this speciation?

• geographic isolation

• temporal isolation

• mechanical isolation

• behavioral isolation

Temporal isolation:

• different breeding seasons/times → no overlap to mate.

​Two species of frogs live in the same pond, but one species breeds in the early spring and the other breeds in the late summer. This is an example of:
a. Habitat isolation
b. Behavioral isolation
c. Mechanical isolation
d. Temporal isolation

Multiple Choice

Although they often live in the same habitat, the American toad breeds earlier in the spring than the Fowler's toad does. The two species do not interbreed due to _____________ isolation.

• temporal
• behavioral
• geographic

Habitat/Ecological isolation:

• same region, different micro-habitats/diets → little/no mating.

Mechanical isolation:

• parts don’t fit; mating cannot occur.

• Sex organs will not physically fit together

• Pollination only occurs with certain pollinators

Multiple Choice

Despite the fact that certain populations of bushbaby share a home, they cannot interbreed.

Since the arrangement of the genitalia in bushbabies differs between species, a male bushbaby of one species cannot effectively copulate with a female bushbaby of another. This is due to

• geographic isolation

• temporal isolation

• behavioral isolation

• mechanical isolation

Gametic isolation:

• sperm and egg incompatible

• differences in the gamete cells, such as incompatible chemical signals

Postzygotic isolation:

• Hybrid Infertility, Inviability, Breakdown

  • hybrid forms but is sterile or weak (e.g., mule from horse × donkey).

​

​When a horse and a donkey mate, they produce a mule, which is sterile and cannot reproduce. This is an example of:
a. Gametic isolation
b. Prezygotic isolation
c. Postzygotic isolation
d. Mechanical isolation

Divergent evolution: related groups become more different after isolation.

• Homologous structures (same underlying structure, different function) support divergence.

​The wing of a bat and the arm of a human have the same underlying bone structure but are used for different functions. These are examples of:
a. Analogous structures
b. Homologous structures
c. Convergent evolution
d. Habitat isolation

Multiple Choice

The forelimbs of a human, a bat, and a whale all share a similar bone structure, but they are used for very different functions (grasping, flying, and swimming). This is evidence of which evolutionary concept?

• Convergent evolution, resulting in analogous structures

• Divergent evolution, resulting in homologous structures.

• Geographic isolation, resulting in speciation.

• Natural selection, resulting in vestigial structures.

Divergent evolution:

• Adaptive radiation: one ancestor → many species as they fill different niches (e.g., Hawaiian honeycreepers, Caribbean anoles).

​Adaptive radiation is when one ancestor evolves into many new species as they fill different ________________.

Multiple Choice

Anoles are a type of lizard that exist as almost 400 different species. An estimated 50 million years ago, populations of Anoles lizards spread to the Caribbean Islands. Many different species of Anoles evolved over time as they adapted to different niches on the islands.

The emergence of different species of anoles is an example of which of the following?

• selective breeding

• bottleneck effect due to near extinction

• divergent evolution

• hybridization

​Convergent evolution (contrast item): unrelated groups evolve similar adaptations in similar environments (e.g., shark vs. dolphin).

• Analogous structures (same function, different structure) support convergence.

• Convergence is not speciation by itself but is often tested alongside it.

​Convergent evolution is when unrelated groups evolve ________________ adaptations in similar environments.

​https://www.youtube.com/watch?v=rdZOwyDbyL0&list=PLI1XjFOSo4gNjRqxxl-eC-H1MyHeO_dUw&index=5

​Anole Convergent Evolution

​https://www.youtube.com/watch?v=udZUaNKXbJA

​Amoeba Sisters - Reproductive Isolation and Speciation

​https://www.youtube.com/watch?v=dfQuDKgwDTo

​Convergent Evolution

​https://youtu.be/1MBPzzXeTPg?feature=shared

​Convergent Evolution - Dolphins and Ichthyosaurs

​https://www.youtube.com/watch?v=X-XtZyHcck4

​Convergent vs Divergent Evolution

https://youtu.be/rdZOwyDbyL0?feature=shared&t=75

​Reproductive Isolation

PRACTICE
Questions

Dropdown

Birds and bats ability to fly has emerged through a process known as ​

Select answer

evolution, where unrelated species independently develop similar traits to adapt to similar environments. They ​

Select answer

share a common ancestor.

Dropdown

Dogs and foxes are similar, ​

Select answer

a common ancestor, a result of ​

Select answer

evolution through natural selection.

Reorder

The process of allopatric speciation occurs in a specific order:

• a population is separated by a physical barrier

• the separated groups evolve independently due to different environmental pressures and genetic drift

• the two groups come back into contact, they are unable to interbreed, meaning they are now two distinct species.

1

2

3

• 1
• 2
• 3

Match

Match the following

• movement of alleles between populations through reproduction

• formation of a new species

• separation of populations by a physical barrier

• inherited trait that improves survival or reproduction in a certain environment

• inability of populations to mate successfully and produce fertile offspring

gene flow

speciation

geographic isolation

adaptation

reproductive isolation

• gene flow

• speciation

• geographic isolation

• adaptation

• reproductive isolation

Match

Match the following

• A canyon splits one squirrel population into two groups.

• Two frog populations live in the same pond but breed in different seasons.

• Pollen moves often between two nearby flower populations.

• Two isolated bird populations develop different beak shapes in different habitats.

• Two populations can no longer produce fertile offspring.

geographic isolation

reproductive isolation

gene flow

independent adaptation

evidence speciation has occurred

• geographic isolation

• reproductive isolation

• gene flow

• independent adaptation

• evidence speciation has occurred

Drag and Drop

When a physical barrier separates one population into two groups, ​

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can occur.

This separation often reduces ​

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between the groups.

As the groups face different environments, they may develop different ​

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over time.

If the groups eventually cannot mate and produce fertile offspring, ​

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has occurred.

An inability to interbreed is evidence of ​

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.

Drag these tiles and drop them in the correct blank above

geographic isolation

gene flow

adaptations

reproductive isolaiton

speciation

Drag and Drop

A whale population that becomes separated from the main population may change over many generations because of ​

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.

As differences build up, the two populations may show different ​

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.

These differences can be used as evidence that the populations are becoming separate ​

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.

The process is most likely to happen when ​

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is reduced for a long period of time.Word Bank: gene flow • DNA • body structures • species • isolation

Drag these tiles and drop them in the correct blank above

isolation

species

gene flow

DNA and body structures

Multiple Choice

A single population of lizards was separated when a river changed course and split the habitat into two isolated sections. Over many generations, the two groups developed different mating behaviors and could no longer reproduce with one another. Which process most likely occurred?

• competition

• speciation

• mimicry

• succession

Multiple Choice

Which statement best explains how geographic isolation can lead to speciation?

• Individuals in two areas instantly become different species after separation.

• Separation reduces gene flow, allowing populations to change independently over time.

• Geographic isolation causes all mutations to stop in both populations.

• Separation guarantees that both populations stay genetically identical.

Multiple Choice

A population of birds becomes separated on two islands. After many generations, the birds still look similar, but they no longer respond to each other’s mating calls. Which statement best describes this situation?

• Speciation has likely occurred because reproductive isolation is present.

• Speciation has not occurred because the birds still live on islands.

• Speciation has likely occurred because both groups are still birds.

• Speciation has not occurred because geographic isolation always prevents evolution.

Multiple Choice

Which example is the best evidence that speciation has occurred?

• Two populations live in different habitats.

• Two populations have different food sources.

• Two populations cannot interbreed and produce fertile offspring.

• Two populations have slightly different body sizes.

Multiple Choice

Before a canyon formed, one squirrel species lived across the area. After the canyon formed, the squirrels were split into two groups on opposite sides. Over time, each group adapted to its own environment. Which statement best explains the most likely result?

• One group immediately became extinct because of competition with humans.

• The separated groups remained identical because the climate was similar.

• The canyon caused reduced gene flow, which could lead to speciation.

• The canyon caused the squirrels to stop reproducing completely.

Multiple Choice

Which situation best shows reproductive isolation rather than geographic isolation?

• A mountain range separates two wolf populations.

• A river separates two frog populations.

• Two insect populations live in the same field but mate at different times of year.

• Two bird populations are separated by an ocean.

Multiple Choice

Scientists study a whale population and find differences in DNA, body structure, and feeding behavior compared with a closely related whale population. Which conclusion is best supported by these data?

• The whale population is definitely younger than the other group.

• The whale population may represent a separate species.

• The whale population cannot have a common ancestor with the other group.

• The whale population must have formed by artificial selection.

Multiple Choice

Which change would most directly increase the chance of speciation between two populations?

• increased movement of individuals between the populations

• increased gene flow between the populations

• long-term separation and different environmental pressures

• mating between the populations every generation

Multiple Choice

A plant species is split by the formation of a desert. One population evolves waxy leaves, and the other evolves broader leaves in a wetter region. Which process best explains these differences?

• reduced gene flow and independent adaptation

• codominance and meiosis

• artificial selection and cloning

• overproduction and carrying capacity

Multiple Choice

Which statement about gene flow is correct?

• Reduced gene flow can increase differences between isolated populations.

• Reduced gene flow can increase differences between isolated populations.
  B. Reduced gene flow makes isolated populations more alike over time.

• Gene flow only occurs in asexual species.

• Gene flow always causes reproductive isolation.

Multiple Choice

Eleven different species of tortoises are found on the Galapagos Islands, and all are different from any species on other continents.  Scientists believe that the tortoises on the islands share a common ancestor with mainland tortoises, so at some point, a mainland tortoise population must have become isolated on the islands.  

Which of the following best explains how the island tortoises became different from the mainland tortoise species?

• Only the island tortoises adapted to their environment and survived.

• Physical separation prevented gene flow and was followed by genetic change.

• The island tortoises interbred with another island tortoise species to form a hybrid species.

• A mutation prevented some of the tortoises from breeding.

Multiple Choice

Geologic activity on an island physically separates a population of animals into two populations.  Many generations later, when the two populations are no longer separated, they do not interbreed.  

What was the most likely evolutionary result of this long period of separation?

• a decrease in variation

• an increase in extinction

• an increase in speciation

• a decrease in diversification

Multiple Choice

The northern spotted owl is a medium-sized, dark brown owl, while the Mexican spotted owl is brown with irregular white and brown spots. The female Mexican spotted owls prefer mating with male Mexican spotted owls though they can mate with the northern spotted owls. A scientist finds that the two species of spotted owls were once the same species.

What will most likely happen if the female Mexican spotted owls continue choosing male Mexican spotted owls over male northern spotted owls?

• Both species will migrate to distant regions.

• Both species will lose the ability to mate with each other.

• Both species will breed with other species of owl.

• Both species will decline their population numbers.

Drag and Drop

Structures that have the same underlying anatomy because they were inherited from a shared common ancestor are called ​

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structures. These structures support divergent evolution, as they often have different functions. In contrast, structures that evolved independently to serve a similar function, like the wing of an insect and the wing of a bird, are called ​

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structures.

Drag these tiles and drop them in the correct blank above

homologous

analogous

vestigial