the origin of species - los angeles mission college 24 - lecture/24... · •speciation, the origin...

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

PowerPoint® Lecture Presentations for

BiologyEighth Edition

Neil Campbell and Jane Reece

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

Chapter 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 Tortoise

Chap 24 - Tortoise.mpg

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

Macroevolution

Chap 24 - Macroevolution.html


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 to

alleles 2, 3, and 4 than to

alleles 5, 6, and 7.

Inference: Gene flow occurred.

Alleles 5, 6, and 7 are more closely

related to one another than to

alleles in population A.

Inference: No gene flow occurred.

Pair of

populations

with detected

gene flow

Estimated minimum

number of gene flow

events to account for

genetic patterns

Distance between

populations (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 to

alleles 2, 3, and 4 than to

alleles 5, 6, and 7.

Inference: Gene flow occurred.

Alleles 5, 6, and 7 are more closely

related to one another than to

alleles in population A.

Inference: No gene flow occurred.

Fig. 24-3b

RESULTS

Pair of

populations

with detected

gene flow

Estimated minimum

number of gene flow

events to account for

genetic patterns

Distance between

populations (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

Individuals

of 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 Ritual

Video: Giraffe Courtship Ritual

Video: Albatross Courtship Ritual

Chap 24 - Boobie Courtship.mpg



Chap 24 - Giraffe Courtship.mpg

Chap 24 - Albatross Courtship.mpg

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 with

stunted 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 0

1 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)

De

gre

e o

f re

pro

du

cti

ve

is

ola

tio

n

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. 24-9

EXPERIMENT

RESULTS

Initial population

Some fliesraised on

starch medium Mating experiments

after 40 generations

Some fliesraised on

maltose medium

FemaleFemale

Starch

Starch Starch

Maltose population 1 population 2

Male S

tarc

hM

alt

ose 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

Fig. 24-9a

EXPERIMENT

Initial population

Some flies

raised onstarch medium Mating experiments

after 40 generations

Some fliesraised on

maltose medium

Fig. 24-9b

RESULTS

FemaleFemale

Starch

Starch Starch

Maltose population 1 population 2

Male S

tarc

hM

alt

ose 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 tetraploid

tissue.

Fig. 24-10-2

2n = 6 4n = 12


tissue.

2n

Gametesproducedare diploid..

Fig. 24-10-3

2n = 6 4n = 12


tissue.

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 range

Yellow-bellied toad,

Bombina variegata

Fire-bellied toad,

Bombina bombina

Allele

fre

qu

en

cy (

log

scale

)

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

fre

qu

en

cy (

log

scale

)

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

of

fem

ale

s

(none)

Females mating

with males from:Ownspecies

Other

species

Sympatric males

Own

speciesOther

species

Allopatric males

0

4

8

12

16

20

24

28

Fig. 24-15a

Sympatric male

pied flycatcher

Allopatric male

pied flycatcher

Fig. 24-15b

Pied flycatchers

Collared flycatchers

28

24

20

16

12

8

4

0

(none)

Nu

mb

er

of

fem

ale

s

Females mating

with males from:

Own

species

Other

species

Sympatric males

Own

species

Other

species

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 location

with 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 for

parent species H. petiolarisRegion diagnostic for

parent 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-UN2

Ancestral 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

the origin of species - los angeles mission college 24 - lecture/24... · •speciation, the origin...

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