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Big Idea #1 Part C. Speciation and Extinction (Rates/adaptive radiation) Role of Reproductive Isolation Populations continue to evolve. Evolution Continues in a Changing Environment. Concept 24.3: Hybrid zones provide opportunities to study factors that cause reproductive isolation.

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big idea 1 part c

Big Idea #1 Part C

Speciation and Extinction (Rates/adaptive radiation)

Role of Reproductive Isolation

Populations continue to evolve

Evolution Continues in a Changing Environment

concept 24 3 hybrid zones provide opportunities to study factors that cause reproductive isolation
Concept 24.3: Hybrid zones provide opportunities to study factors that cause reproductive isolation
  • A hybrid zoneis a region in which members of different species mate and produce hybrids
patterns within hybrid zones
Patterns Within Hybrid Zones
  • A hybrid zone can occur in a single band where adjacent species meet
  • Hybrids often have reduced fitness compared with parent species
  • The distribution of hybrid zones can be more complex if parent species are found in multiple habitats within the same region
slide4

Fig. 24-13

EUROPE

Fire-bellied

toad range

Hybrid zone

Fire-bellied toad,

Bombina bombina

Yellow-bellied

toad range

Yellow-bellied toad,

Bombina variegata

0.99

0.9

Allele frequency (log scale)

0.5

0.1

0.01

20

40

30

10

0

10

20

Distance from hybrid zone center (km)

slide5

Fig. 24-13a

Yellow-bellied toad,

Bombina variegata

fig 24 13b
Fig. 24-13b

Fire-bellied toad, Bombina bombina

slide7

Fig. 24-13c

Fire-bellied

toad range

Hybrid zone

Yellow-bellied

toad range

0.99

0.9

Allele frequency (log scale)

0.5

0.1

0.01

20

10

0

40

30

20

10

Distance from hybrid zone center (km)

hybrid zones over time
Hybrid Zones over Time

When closely related species meet in a hybrid zone, there are three possible outcomes:

  • Strengthening of reproductive barriers
  • Weakening of reproductive barriers
  • Continued formation of hybrid individuals
slide9

Fig. 24-14-1

Gene flow

Barrier to

gene flow

Population

(five individuals

are shown)

slide10

Fig. 24-14-2

Isolated population

diverges

Gene flow

Barrier to

gene flow

Population

(five individuals

are shown)

slide11

Fig. 24-14-3

Isolated population

diverges

Hybrid

zone

Gene flow

Hybrid

Barrier to

gene flow

Population

(five individuals

are shown)

slide12

Fig. 24-14-4

Isolated population

diverges

Possible

outcomes:

Hybrid

zone

Reinforcement

OR

Fusion

Gene flow

Hybrid

OR

Barrier to

gene flow

Population

(five individuals

are shown)

Stability

reinforcement strengthening reproductive barriers
Reinforcement: Strengthening Reproductive Barriers
  • The reinforcementof barriers occurs when hybrids are less fit than the parent species
  • Over time, the rate of hybridization decreases
  • Where reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species
slide14

Fig. 24-15

Allopatric male

pied flycatcher

Sympatric male

pied flycatcher

28

Pied flycatchers

24

Collared flycatchers

20

16

Number of females

12

8

4

(none)

0

Females mating

with males from:

Other

species

Own

species

Own

species

Other

species

Sympatric males

Allopatric males

slide15

Fig. 24-15a

Allopatric male

pied flycatcher

Sympatric male

pied flycatcher

slide16

Fig. 24-15b

28

Pied flycatchers

24

Collared flycatchers

20

16

Number of females

12

8

4

(none)

0

Other

species

Own

species

Other

species

Females mating

with males from:

Own

species

Sympatric males

Allopatric males

fusion weakening reproductive barriers
Fusion: Weakening Reproductive Barriers
  • If hybrids are as fit as parents, there can be substantial gene flow between species
  • If gene flow is great enough, the parent species can fuse into a single species
slide18

Fig. 24-16

Pundamilia nyererei

Pundamilia pundamilia

Pundamilia “turbid water,”

hybrid offspring from a location

with turbid water

stability continued formation of hybrid individuals
Stability: Continued Formation of Hybrid Individuals
  • Extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone
  • In cases where hybrids have increased fitness, local extinctions of parent species within the hybrid zone can prevent the breakdown of reproductive barriers
slide20
Concept 24.4: Speciation can occur rapidly or slowly and can result from changes in few or many genes

Many questions remain concerning how long it takes for new species to form, or how many genes need to differ between species

the time course of speciation
The Time Course of Speciation
  • Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data
patterns in the fossil record
Patterns in the Fossil Record
  • The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear
  • Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibriumto describe periods of apparent stasis punctuated by sudden change
  • The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence
slide23

Fig. 24-17

(a) Punctuated pattern

Time

(b) Gradual pattern

speciation rates
Speciation Rates
  • The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid
  • The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years
slide25

Fig. 24-18

(a) The wild sunflower Helianthus anomalus

H. anomalus

Chromosome 1

Experimental hybrid

H. anomalus

Chromosome 2

Experimental hybrid

H. anomalus

Chromosome 3

Experimental hybrid

Key

Region diagnostic for

parent species H. annuus

Region diagnostic for

parent species H. petiolaris

Region lacking information on parental origin

(b) The genetic composition of three chromosomes in H.

anomalus and in experimental hybrids

slide26

Fig. 24-18a

(a) The wild sunflower Helianthus anomalus

slide27

Fig. 24-18b

H. anomalus

Chromosome 1

Experimental hybrid

H. anomalus

Chromosome 2

Experimental hybrid

H. anomalus

Chromosome 3

Experimental hybrid

Key

Region diagnostic for

parent species H. petiolaris

Region diagnostic for

parent species H. annuus

Region lacking information on parental origin

(b) The genetic composition of three chromosomes in H.

anomalus and in experimental hybrids

studying the genetics of speciation
Studying the Genetics of Speciation
  • The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation
  • Depending on the species in question, speciation might require the change of only a single allele or many alleles
slide30

Fig. 24-20

(a) Typical Mimulus lewisii

(b) M. lewisii with an M. cardinalis flower-color allele

(c) Typical Mimulus cardinalis

(d) M. cardinalis with an M. lewisii flower-color allele

from speciation to macroevolution
From Speciation to Macroevolution
  • Macroevolution is the cumulative effect of many speciation and extinction events
slide32

Fig. 24-UN1

Original population

Allopatric speciation

Sympatric speciation

slide33

Fig. 24-UN2

Ancestral species:

AA

BB

DD

Wild

T. tauschii

(2n = 14)

Triticum

monococcum

(2n = 14)

Wild

Triticum

(2n = 14)

Product:

AA BB DD

T. aestivum

(bread wheat)

(2n = 42)

you should now be able to
You should now be able to:
  • Define and discuss the limitations of the four species concepts
  • Describe and provide examples of prezygotic and postzygotic reproductive barriers
  • Distinguish between and provide examples of allopatric and sympatric speciation
  • Explain how polyploidy can cause reproductive isolation
  • Define the term hybrid zone and describe three outcomes for hybrid zones over time
slide36
Concept 25.4: The rise and fall of dominant groups reflect continental drift, mass extinctions, and adaptive radiations
  • The history of life on Earth has seen the rise and fall of many groups of organisms

Video: Volcanic Eruption

Video: Lava Flow

continental drift
Continental Drift
  • At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago
  • Earth’s continents move slowly over the underlying hot mantle through the process of continental drift
  • Oceanic and continental plates can collide, separate, or slide past each other
  • Interactions between plates cause the formation of mountains and islands, and earthquakes
slide38

Fig. 25-12

North

American

Plate

Eurasian Plate

Crust

Caribbean

Plate

Philippine

Plate

Juan de Fuca

Plate

Arabian

Plate

Indian

Plate

Cocos Plate

Mantle

South

American

Plate

Pacific

Plate

Nazca

Plate

African

Plate

Outer

core

Australian

Plate

Inner

core

Antarctic

Plate

Scotia Plate

(b) Major continental plates

(a) Cutaway view of Earth

slide39

Fig. 25-12a

Crust

Mantle

Outer

core

Inner

core

(a) Cutaway view of Earth

slide40

Fig. 25-12b

North

American

Plate

Eurasian Plate

Caribbean

Plate

Philippine

Plate

Juan de Fuca

Plate

Arabian

Plate

Indian

Plate

Cocos Plate

South

American

Plate

Pacific

Plate

Nazca

Plate

African

Plate

Australian

Plate

Antarctic

Plate

Scotia Plate

(b) Major continental plates

consequences of continental drift
Consequences of Continental Drift
  • Formation of the supercontinent Pangaeaabout 250 million years ago had many effects
    • A reduction in shallow water habitat
    • A colder and drier climate inland
    • Changes in climate as continents moved toward and away from the poles
    • Changes in ocean circulation patterns leading to global cooling
slide42

Fig. 25-13

Present

Cenozoic

Eurasia

North America

Africa

65.5

India

South

America

Madagascar

Australia

Antarctica

Laurasia

135

Mesozoic

Gondwana

Millions of years ago

Pangaea

251

Paleozoic

slide43

Fig. 25-13a

Present

Cenozoic

North America

Eurasia

Millions of years ago

Africa

65.5

India

South

America

Madagascar

Australia

Antarctica

slide44

Fig. 25-13b

Laurasia

135

Gondwana

Mesozoic

Millions of years ago

251

Pangaea

Paleozoic

slide45

The break-up of Pangaea lead to allopatric speciation

  • The current distribution of fossils reflects the movement of continental drift
  • For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached
mass extinctions
Mass Extinctions
  • The fossil record shows that most species that have ever lived are now extinct
  • At times, the rate of extinction has increased dramatically and caused a mass extinction
the big five mass extinction events
The “Big Five” Mass Extinction Events
  • In each of the five mass extinction events, more than 50% of Earth’s species became extinct
slide48

Fig. 25-14

800

20

700

600

15

500

Number of families:

400

Total extinction rate

(families per million years):

10

300

200

5

100

0

0

Mesozoic

Paleozoic

Cenozoic

Era

Period

E

C

Tr

C

O

S

D

P

J

P

N

200

145

65.5

0

542

488

444

416

359

299

251

Time (millions of years ago)

slide49

The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras

  • This mass extinction occurred in less than 5 million years and caused the extinction of about 96% of marine animal species
  • This event might have been caused by volcanism, which lead to global warming, and a decrease in oceanic oxygen
slide50

The Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic

  • Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs
slide51

Fig. 25-15

NORTH

AMERICA

Chicxulub

crater

Yucatán

Peninsula

slide52

The presence of iridium in sedimentary rocks suggests a meteorite impact about 65 million years ago

  • The Chicxulub crater off the coast of Mexico is evidence of a meteorite that dates to the same time
is a sixth mass extinction under way
Is a Sixth Mass Extinction Under Way?
  • Scientists estimate that the current rate of extinction is 100 to 1,000 times the typical background rate
  • Data suggest that a sixth human-caused mass extinction is likely to occur unless dramatic action is taken
consequences of mass extinctions
Consequences of Mass Extinctions
  • Mass extinction can alter ecological communities and the niches available to organisms
  • It can take from 5 to 100 million years for diversity to recover following a mass extinction
  • Mass extinction can pave the way for adaptive radiations
slide55

Fig. 25-16

50

40

30

Predator genera

(percentage of marine genera)

20

10

0

Cenozoic

Paleozoic

Mesozoic

Era

Period

P

D

C

P

C

N

E

O

J

S

Tr

200

145

359

65.5

0

488

444

542

416

299

251

Time (millions of years ago)

adaptive radiations
Adaptive Radiations
  • Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities
worldwide adaptive radiations
Worldwide Adaptive Radiations
  • Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs
  • The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size
  • Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods
slide58

Fig. 25-17

Ancestral

mammal

Monotremes

(5 species)

ANCESTRAL

CYNODONT

Marsupials

(324 species)

Eutherians

(placental

mammals;

5,010 species)

50

200

250

100

150

0

Millions of years ago

regional adaptive radiations
Regional Adaptive Radiations
  • Adaptive radiations can occur when organisms colonize new environments with little competition
  • The Hawaiian Islands are one of the world’s great showcases of adaptive radiation
slide60

Fig. 25-18

Close North American relative,

the tarweed Carlquistia muirii

1.3

million

years

MOLOKAI

KAUAI

5.1

million

years

Dubautia laxa

MAUI

OAHU

3.7

million

years

Argyroxiphiumsandwicense

LANAI

HAWAII

0.4

million

years

Dubautia waialealae

Dubautia scabra

Dubautia linearis

slide61

Fig. 25-18a

1.3

million

years

KAUAI

5.1

million

years

MOLOKAI

MAUI

OAHU

3.7

million

years

LANAI

HAWAII

0.4

million

years

slide62

Fig. 25-18b

Close North American relative,

the tarweed Carlquistia muirii

slide63

Fig. 25-18c

Dubautia waialealae

slide64

Fig. 25-18d

Dubautia laxa

slide65

Fig. 25-18e

Dubautia scabra

slide66

Fig. 25-18f

Argyroxiphium sandwicense

slide67

Fig. 25-18g

Dubautia linearis