ohhs ap bio chapter 24 presentation

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 24Chapter 24

The Origin of Species


Overview: That “Mystery of Mysteries”

• In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth

Video: Galápagos TortoiseVideo: Galápagos Tortoise

Fig. 24-1


• Speciation, the origin of new species, is at the focal point of evolutionary theory

• Evolutionary theory must explain how new species originate and how populations evolve

• Microevolution consists of adaptations that evolve within a population, confined to one gene pool

• Macroevolution refers to evolutionary change above the species level

Animation: MacroevolutionAnimation: Macroevolution


Concept 24.1: The biological species concept emphasizes reproductive isolation

• Species is a Latin word meaning “kind” or “appearance”

• Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms


The Biological Species Concept

• The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations

• Gene flow between populations holds the phenotype of a population together

Fig. 24-2

(a) Similarity between different species

(b) Diversity within a species

Fig. 24-2a

(a) Similarity between different species

Fig. 24-2b

(b) Diversity within a species

Fig. 24-3

EXPERIMENT

RESULTS

Example of a gene tree for population pair A-B

Allele PopulationGene flow event 1 B

B

B

B

5

6

7

2

3

4

A

A

A

Allele 1 is more closely related toalleles 2, 3, and 4 than toalleles 5, 6, and 7.Inference: Gene flow occurred.

Alleles 5, 6, and 7 are more closelyrelated to one another than toalleles in population A.Inference: No gene flow occurred.

Pair ofpopulationswith detectedgene flow

Estimated minimumnumber of gene flowevents to account forgenetic patterns

Distance betweenpopulations (km)

A-B

K-L

A-C

B-C

F-G

G-I

C-E

5

3

2–3

2

2

2

1–2

340

720

1,390

1,190

1,110

760

1,310

Fig. 24-3a

EXPERIMENT

Example of a gene tree for population pair A-B

Allele PopulationGene flow event 1 B

B

B

B

5

6

7

2

3

4

A

A

A

Allele 1 is more closely related toalleles 2, 3, and 4 than toalleles 5, 6, and 7.Inference: Gene flow occurred.

Alleles 5, 6, and 7 are more closelyrelated to one another than toalleles in population A.Inference: No gene flow occurred.

Fig. 24-3b

RESULTS

Pair ofpopulationswith detectedgene flow

Estimated minimumnumber of gene flowevents to account forgenetic patterns

Distance betweenpopulations (km)

A-B

K-L

A-C

B-C

F-G

G-I

C-E

5

3

2–3

2

2

2

1–2

340

720

1,390

1,190

760

1,110

1,310

Fig. 24-3c

Grey-crowned babblers


Reproductive Isolation

• Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring

• Hybrids are the offspring of crosses between different species

• Reproductive isolation can be classified by whether factors act before or after fertilization


• Prezygotic barriers block fertilization from occurring by:

– Impeding different species from attempting to mate

– Preventing the successful completion of mating

– Hindering fertilization if mating is successful


• Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers

Fig. 24-4

Prezygotic barriers

Habitat Isolation

Individualsof

differentspecies

Temporal Isolation Behavioral Isolation

Matingattempt

Mechanical Isolation Gametic Isolation

Fertilization

Reduced Hybrid Viability Reduced Hybrid Fertility

Postzygotic barriers

Hybrid Breakdown

Viable,fertile

offspring

(a)

(b)

(d)

(c) (e) (f) (g) (h) (i)

(j)

(l)

(k)

Fig. 24-4a

Habitat Isolation Temporal Isolation

Prezygotic barriers

Behavioral Isolation

Matingattempt

Mechanical Isolation

(f)(e)(c)(a)

(b)

(d)

Individualsof

differentspecies

Fig. 24-4i

Prezygotic barriers

Gametic Isolation

Fertilization

Reduced Hybrid Viability


Reduced Hybrid Fertility Hybrid Breakdown

Viable,fertile

offspring

(g) (h) (i)

(j)

(l)

(k)

Fig. 24-4b

Prezygotic barriers

Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation

Individualsof

differentspecies

Matingattempt

Prezygotic barriers

Fig. 24-4j

Gametic Isolation

Fertilization

Reduced Hybrid Viability Reduced Hybrid Fertility


Hybrid Breakdown

Viable,fertile

offspring

Fig. 24-4c

(a)

Water-dwelling Thamnophis

Fig. 24-4d

(b)

Terrestrial Thamnophis


• Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes

Fig. 24-4e

(c)

Eastern spotted skunk(Spilogale putorius)

Fig. 24-4f

(d)

Western spotted skunk(Spilogale gracilis)


• Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers

Video: Blue-footed Boobies Courtship RitualVideo: Blue-footed Boobies Courtship Ritual

Video: Giraffe Courtship RitualVideo: Giraffe Courtship Ritual

Video: Albatross Courtship RitualVideo: Albatross Courtship Ritual

Fig. 24-4g

(e)

Courtship ritual of blue-footed boobies


• Mechanical isolation: Morphological differences can prevent successful mating

Fig. 24-4h

(f)

Bradybaena with shellsspiraling in oppositedirections


• Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species

Fig. 24-4k

(g)

Sea urchins


• Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult:

– Reduced hybrid viability

– Reduced hybrid fertility

– Hybrid breakdown


• Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development

Fig. 24-4l

(h)

Ensatina hybrid


• Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile

Fig. 24-4m

(i)

Donkey

Fig. 24-4n

( j)

Horse

Fig. 24-4o

(k)

Mule (sterile hybrid)


• Hybrid breakdown: Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile

Fig. 24-4p

(l)

Hybrid cultivated rice plants withstunted offspring (center)


Limitations of the Biological Species Concept

• The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)


Other Definitions of Species

• Other species concepts emphasize the unity within a species rather than the separateness of different species

• The morphological species concept defines a species by structural features

– It applies to sexual and asexual species but relies on subjective criteria


• The ecological species concept views a species in terms of its ecological niche

– It applies to sexual and asexual species and emphasizes the role of disruptive selection

• The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree

– It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species


Concept 24.2: Speciation can take place with or without geographic separation

• Speciation can occur in two ways:

– Allopatric speciation

– Sympatric speciation

Fig. 24-5

(a) Allopatric speciation (b) Sympatric speciation


Allopatric (“Other Country”) Speciation

• In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations


The Process of Allopatric Speciation

• The definition of barrier depends on the ability of a population to disperse

• Separate populations may evolve independently through mutation, natural selection, and genetic drift

Fig. 24-6

A. harrisi A. leucurus


Evidence of Allopatric Speciation

• Regions with many geographic barriers typically have more species than do regions with fewer barriers

Fig. 24-7

Mantellinae(Madagascar only):100 species

Rhacophorinae(India/SoutheastAsia): 310 species

Other Indian/Southeast Asianfrogs

Millions of years ago (mya)1 2 3

1 2 3

100 80 60 40 20 0

88 mya 65 mya 56 mya

India

Madagascar

Fig. 24-7a

Mantellinae(Madagascar only):100 species

Rhacophorinae(India/SoutheastAsia): 310 species

Other Indian/Southeast Asianfrogs

Millions of years ago (mya)

100 80 60 40 20 01 2 3

Fig. 24-7b

India

88 mya 65 mya 56 mya

Madagascar

1 2 3


• Reproductive isolation between populations generally increases as the distance between them increases

Fig. 24-8

Geographic distance (km)

Deg

ree

of

rep

rod

uct

ive

iso

lati

on

00

50 100 150 250200 300

0.5

1.0

1.5

2.0


• Barriers to reproduction are intrinsic; separation itself is not a biological barrier

Fig. 24-9EXPERIMENT

RESULTS

Initial population

Some fliesraised on

starch medium Mating experimentsafter 40 generations

Some fliesraised on

maltose medium

FemaleFemale

StarchStarch Starch

Maltose population 1 population 2

Mal

e Sta

rch

Mal

tose

Mal

eS

tarc

hS

tarc

hp

op

ula

tio

n 1

po

pu

lati

on

2

22

8 20

9 18

12

15

15

Mating frequenciesin experimental group

Mating frequenciesin control group

Fig. 24-9a

EXPERIMENT

Initial population

Some fliesraised on

starch medium Mating experimentsafter 40 generations

Some fliesraised on

maltose medium

Fig. 24-9b

RESULTS

FemaleFemale

StarchStarch Starch

Maltose population 1 population 2

Mal

e Sta

rch

Mal

tose M

ale

Sta

rch

Sta

rch

po

pu

lati

on

1p

op

ula

tio

n 2

22

8 20

9 18

12

15

15

Mating frequenciesin experimental group

Mating frequenciesin control group


Sympatric (“Same Country”) Speciation

• In sympatric speciation, speciation takes place in geographically overlapping populations


Polyploidy

• Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division

• An autopolyploid is an individual with more than two chromosome sets, derived from one species

Fig. 24-10-1

2n = 6 4n = 12

Failure of celldivision afterchromosomeduplication givesrise to tetraploidtissue.

Fig. 24-10-2

2n = 6 4n = 12


2n

Gametesproducedare diploid..

Fig. 24-10-3

2n = 6 4n = 12


2n

Gametesproducedare diploid..

4n

Offspring withtetraploidkaryotypes maybe viable andfertile.


• An allopolyploid is a species with multiple sets of chromosomes derived from different species

Fig. 24-11-1

Species A2n = 6

Normalgameten = 3

Meioticerror

Species B2n = 4

Unreducedgametewith 4chromosomes

Fig. 24-11-2

Species A2n = 6

Normalgameten = 3

Meioticerror

Species B2n = 4


Hybridwith 7chromosomes

Fig. 24-11-3

Species A2n = 6

Normalgameten = 3

Meioticerror

Species B2n = 4




Normalgameten = 3

Fig. 24-11-4

Species A2n = 6

Normalgameten = 3

Meioticerror

Species B2n = 4




Normalgameten = 3

Viable fertilehybrid(allopolyploid)2n = 10


• Polyploidy is much more common in plants than in animals

• Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids


Habitat Differentiation

• Sympatric speciation can also result from the appearance of new ecological niches

• For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees


Sexual Selection

• Sexual selection can drive sympatric speciation

• Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria

Fig. 24-12

EXPERIMENT

Normal lightMonochromatic

orange light

P.pundamilia

P. nyererei


Allopatric and Sympatric Speciation: A Review

• In allopatric speciation, geographic isolation restricts gene flow between populations

• Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations

• Even if contact is restored between populations, interbreeding is prevented


• In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species

• Sympatric speciation can result from polyploidy, natural selection, or sexual selection


Concept 24.3: Hybrid zones provide opportunities to study factors that cause reproductive isolation

• A hybrid zone is a region in which members of different species mate and produce hybrids


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

Fig. 24-13

EUROPE

Fire-belliedtoad range

Hybrid zone

Yellow-belliedtoad rangeYellow-bellied toad,

Bombina variegata

Fire-bellied toad,Bombina bombina

Alle

le f

req

uen

cy (

log

sca

le)

Distance from hybrid zone center (km)

40 30 20 2010 100

0.01

0.1

0.5

0.9

0.99

Fig. 24-13a

Yellow-bellied toad,Bombina variegata

Fig. 24-13b

Fire-bellied toad, Bombina bombina

Fig. 24-13c

Fire-belliedtoad range

Yellow-belliedtoad range

Hybrid zone

All

ele

freq

uen

cy (

log

sca

le)

Distance from hybrid zone center (km)40 30 20 2010 100

0.01

0.1

0.5

0.9

0.99


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

Fig. 24-14-1

Gene flow

Population(five individualsare shown)

Barrier togene flow

Fig. 24-14-2

Gene flow


Barrier togene flow

Isolated populationdiverges

Fig. 24-14-3

Gene flow


Barrier togene flow


Hybridzone

Hybrid

Fig. 24-14-4

Gene flow


Barrier togene flow


Hybridzone

Hybrid

Possibleoutcomes:

Reinforcement

OR

OR

Fusion

Stability


Reinforcement: Strengthening Reproductive Barriers

• The reinforcement of 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

Fig. 24-15

Sympatric malepied flycatcher

Allopatric malepied flycatcher

Pied flycatchers

Collared flycatchers

Nu

mb

er o

f fe

mal

es

(none)

Females matingwith males from:

Ownspecies

Otherspecies

Sympatric males

Ownspecies

Otherspecies

Allopatric males

0

4

8

12

16

20

24

28

Fig. 24-15a

Sympatric malepied flycatcher

Allopatric malepied flycatcher

Fig. 24-15b

Pied flycatchers

Collared flycatchers

28

24

20

16

12

8

4

0

(none)

Nu

mb

er o

f fe

mal

es

Females matingwith males from:

Ownspecies

Otherspecies

Sympatric males

Ownspecies

Otherspecies

Allopatric males


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

Fig. 24-16

Pundamilia nyererei Pundamilia pundamilia

Pundamilia “turbid water,”hybrid offspring from a locationwith turbid water


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


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

• Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data


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 equilibrium to describe periods of apparent stasis punctuated by sudden change

• The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence

Fig. 24-17

(a) Punctuated pattern

(b) Gradual pattern

Time


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

Fig. 24-18

(a) The wild sunflower Helianthus anomalus

H. anomalus

H. anomalus

H. anomalus

(b) The genetic composition of three chromosomes in H. anomalus and in experimental hybrids

Chromosome 1

Chromosome 2

Chromosome 3

Experimental hybrid

Experimental hybrid

Experimental hybrid

Key

Region diagnostic forparent species H. petiolaris

Region diagnostic forparent species H. annuus

Region lacking information on parental origin

Fig. 24-18a

(a) The wild sunflower Helianthus anomalus

Fig. 24-18b

(b) The genetic composition of three chromosomes in H. anomalus and in experimental hybrids

Region lacking information on parental origin

Region diagnostic forparent species H. petiolaris

Region diagnostic forparent species H. annuus

Key

Experimental hybrid

Experimental hybrid

Experimental hybrid

Chromosome 3

Chromosome 2

Chromosome 1

H. anomalus

H. anomalus

H. anomalus


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

Fig. 24-19

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

• Macroevolution is the cumulative effect of many speciation and extinction events

Fig. 24-UN1

Original population

Allopatric speciation Sympatric speciation

Fig. 24-UN2Ancestral species:

Triticummonococcum(2n = 14)

AA BB

WildTriticum(2n = 14)

Product:

AA BB DD

T. aestivum(bread wheat)(2n = 42)

WildT. tauschii(2n = 14)

DD

Fig. 24-UN3


You should now be able to:

1. Define and discuss the limitations of the four species concepts

2. Describe and provide examples of prezygotic and postzygotic reproductive barriers

3. Distinguish between and provide examples of allopatric and sympatric speciation

4. Explain how polyploidy can cause reproductive isolation

5. Define the term hybrid zone and describe three outcomes for hybrid zones over time

ohhs ap bio chapter 24 presentation

Education

b b b b

b b diversity

different species b

populations gene flow

origin of species

d b terrestrialthamnophis

detected gene flow

b results pair of populations