10.4 Lesson (Sem) - Speciation

​Lesson - Speciation

• ​What do you think these lizards will NOT mate together?

• 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 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 that forms a new species when populations become reproductively isolated and 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

• Natural selection favors different traits in different environments.

• Genetic drift (chance events), especially in small populations, changes allele frequencies

3. Reproductive isolation:

• Even if contact is restored, groups cannot or do not produce fertile offspring.

• Result: new species.

​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

• diverging species no longer recognize one another as potential mates.

• diverging species mate exclusively.

• diverging species mate with multiple members of the other species.

• diverging species recognize many potential mates among both species.

​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

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

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

Posyzygotic 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

Dropdown

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 ​

Select answer

isolation.

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

Drag and Drop

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

Placeholder

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 ​

Placeholder

structures.

Drag these tiles and drop them in the correct blank above

homologous

analogous

vestigial

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

Dropdown

Dogs and foxes are similar, ​

Select answer

a common ancestor, a result of ​

Select answer

evolution through natural selection.

​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.

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.

​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

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 result of natural selection during this 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.