1. Biology, 9th ed,Sylvia Mader
Chapter 18
Processes of Evolution
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
Ensatina eschscholtzi picta 1
Members of a northern ancestral
population migrated southward.
Ensatina eschscholtzi
oregonensis
horse
mating
donkey 2
Subspecies are separated by
California’s Central Valley .Some
interbreeding between populations
does occur.
fertilization
Central
Valley
Barrier
Ensatina eschscholtzi platensis
Ensatina eschscholtzi
xanthoptica
Ensatina eschscholtzi
croceater
Usually
mules cannot
offspring
If an
reproduce.
it cannot
does result,
mule (hybrid)
Ensatina eschscholtzi
eschscholtzii
(Stallion): © Superstock, Inc.; (Donkey): © Robert J. Erwin/Photo Researchers, Inc.; (Mule): © Jorg & Petra Wegner/Animals Animals/Earth Scenes;
Offspring
Ensatina eschscholtzi
klauberi 3
Evolution has occurred, and in the south, subspecies do not interbreed even though they live in the same environment.

2. Outline Separation of the Species Modes of Separation Macroevolution
Allopatic speciation
Adaptive radiation
Sympatric speciation
Macroevolution

3. Separation of the Species
Macroevolution is best observed within the fossil record,
Requires the origin of species, also called speciation.
Speciation is the final result of changes in gene pool allelic and genotypic frequencies.

4. Species Definitions Every species has its own evolutionary history
Binomial nomenclature, is used to name various species
The two-part scientific name, when translated from the Latin, often tells you something about the organism.
Scientific name of the dinosaur, Tyrannosaurus rex, means “tyrant-lizard king.”

5. Species Definitions
Evolutionary species concept distinguish species from one another based on:
Morphological (structural) traits,
Biological species concept relies primarily on reproductive isolation rather than trait differences to define a species.

6. Species Definitions Species Definitions Morphological
Can be distinguished anatomically
Specialist decides what criteria probably represent reproductively isolated populations
Most species described this way

7. Evolutionary Species Concept
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Orcinus orca
Hindlimbs too
reduced for walking
or swimming
Rodhocetus kasrani
Ambulocetus natans
Hindlimbs used
for both walking
on land and
paddling in water
Tetrapod with limbs
for walking
Pakicetus attocki

8. Species Definitions Species Definitions Biological
Populations of the same species breed only among themselves
Are reproductively isolated from other such populations
Very few actually tested for reproductive isolation

9. Biological Species Concept
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pit-see
fitz-bew
che-bek or che-bek
Acadian flycatcher , Empidonax virescens
Willow flycatcher, Empidonax trailli
Least flycatcher, Empidonax minimus
(Acadian): © Karl Maslowski/Visuals Unlimited; (Willow): © Ralph Reinhold/Animals Animals/Earth Scenes; (Least): © Stanley Maslowski/Visuals Unlimited.

10. Human Populations
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(Left): © Sylvia S. Mader; (Right): © B & C Alexander/Photo Researchers, Inc.

11. Reproductive Isolating Mechanisms
Reproductive isolating mechanisms inhibit gene flow between species
Two general types:
(1) Prezygotic Mechanisms – prevents matting attempts
Habitat Isolation - species occupy different habitats,
Temporal Isolation - each reproduces at a different time
Behavioral Isolation
Mechanical Isolation
Gamete Isolation

12. Reproductive Barrier Prezygotic Isolating Mechanisms
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Prezygotic Isolating Mechanisms
Postzygotic Isolating Mechanisms
Premating
Mating
Fertilization
Habitat isolation
Species at same locale
occupy different habitats.
Zygote mortality
Fertilization occurs, but
zygote does not survive.
species 1
Mechanical isolation
Genitalia between
species are unsuitable
for one another.
hybrid
offspring
Temporal isolation
Species reproduce at
different seasons or
different times of day.
Hybrid sterility
Hybrid survives but is
sterile and cannot
reproduce.
species 2
Behavioral isolation
In animal species,
courtship behavior differs,
or individuals respond to
different songs, calls,
pheromones, or other
signals.
Gamete isolation
Sperm cannot reach
or fertilize egg.
F2 fitness
Hybrid is fertile, but F2 hybrid
has reduced fitness.

13. Temporal Isolation high low March 1 April 1 May 1 June 1 July 1
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high
leopard frog
pickerel frog
wood frog
green frog
bullfrog
Mating Activity
low
March 1
April 1
May 1
June 1
July 1

14. Prezygotic Isolating Mechanism
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© Barbara Gerlach/Visuals Unlimited

15. Reproductive Isolating Mechanisms
Two general types:
(2) Postzygotic Mechanisms - Prevent hybrid offspring from developing or breeding
Zygote Mortality
Hybrid Sterility
Reduced F2 Fitness

16. Postzygotic Isolating Mechanism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
horse
donkey
mating
fertilization
Usually
mules cannot
reproduce.
If an
offspring
does result,
it cannot
mule (hybrid)
Offspring
(Stallion): © Superstock, Inc.; (Donkey): © Robert J. Erwin/Photo Researchers, Inc.; (Mule): © Jorg & Petra Wegner/Animals Animals/Earth Scenes;

17. Modes of Speciation Speciation: Two modes:
The splitting of one species into two, or
The transformation of one species into a new species over time
Two modes:
(1) Allopatric Speciation
Two geographically isolated populations of one species
Become different species over time
Can be due to differing selection pressures in differing environments

18. Allopatric Speciation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ensatina eschscholtzi picta 1
Members of a northern ancestral
population migrated southward.
Ensatina eschscholtzi
oregonensis 2
Subspecies are separated by
California’s Central Valley .Some
interbreeding between populations
does occur.
Central
Valley
Barrier
Ensatina eschscholtzi platensis
Ensatina eschscholtzi
xanthoptica
Ensatina eschscholtzi
croceater
Ensatina eschscholtzi
eschscholtzii
Ensatina eschscholtzi
klauberi 3
Evolution has occurred, and in the south, subspecies do not interbreed even though they live in the same environment.

19. Allopatric Speciation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lake male
River male
Lake female
River female
a. Sockeye salmon at Pleasure Point Beach, Lake Washington
b. Sockeye salmon in Cedar River .The river connects with
Lake Washington.
Salmon that matured at Pleasure Point Beach do not reproduce with those that matured in the Cedar River.

20. Modes of Speciation Two modes: (2) Sympatric Speciation
One population develops into two or more reproductively isolated groups
No prior geographic isolation
It involves polyploidy (a chromosome number beyond the diploid [2n] number)
Tetraploid hybridization in plants
Results in self fertile species
Reproductively isolated from either parental species 20

21. Modes of Speciation (2) Sympatric Speciation
A polyploid plant can reproduce with itself, but cannot reproduce with the 2n population because not all the chromosomes would be able to pair during meiosis.
Two types of polyploidy are known:
Autoploidy - diploid plant produces diploid gametes due to nondisjunction during meiosis.
If diploid gamete fuses with a haploid gamete, a triploid plant results.
A triploid (3n) plant is sterile and cannot produce offspring because the chromosomes cannot pair during meiosis.
Alloploidy - more complicated process than autoploidy
Requires two different but related species of plants Hybridization is followed by doubling of the chromosomes. 21

22. Alloploidy no seeds seeds diploid banana (2n) polyploid banana 22
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. no
seeds
seeds
diploid
banana (2n)
polyploid
banana 22

23. Autoploidy 23 Clarkia concinna Clarkia virgata hybrid
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2n = 14
2n = 10
Clarkia concinna
Clarkia virgata
hybrid
doubling of chromosome number
2n = 24
Clarkia pulchella
(C. pulchella): © J. L. Reveal; (C. concinna): © Gerald & Buff Corsi/Visuals Unlimited; (C. virgata): ©: Dr. Dean Wm. Taylor/Jepson Herbarium, UC Berkeley 23

24. Adaptive Radiation Adaptive Radiation
When members of a species invade several new geographically separate environments
The populations become adapted to the different environments
Many new species evolve from the single ancestral species
This is an example of allopatric speciation 24

25. Adaptive Radiation 25 Genus Pseudonestor Genus Loxops
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
* Lesser Koa finch
Palila
Laysan
finch
* Greater
Koa finch
Genus Psittirostra Ou
Maui parrot bill
* Kona
finch
Genus Pseudonestor
Akiapolaau
* Kauai
akialoa
Nukupuu
Genus Loxops *
Akialoa
Genus Loxops
Genus Hemignathus
Great
amakihi
(green
solitaire)
Anianiau
(lesser
amakihi)
* Extinct species or subspecies
Alauwahio
(Hawaiian
creeper)
Akepa
Amakihi 25

26. Principles of Macroevolution
Evolution at the species or higher level of classification
Occurs gradually
Evolutionists support a gradualistic model
Speciation occurs after populations become isolated
Each group continuing its own evolutionary pathway
The gradualistic model suggests that it is difficult to indicate when speciation occurred 26

27. Principles of Macroevolution
Some paleontologists believe that
Species can appear quite suddenly
Remain essentially unchanged phenotypically during a period of stasis (sameness) until they undergo extinction.
Based on these findings, they developed a punctuated equilibrium model to explain the pace of evolution. 27

28. Gradualistic and Punctuated Equilibrium Models
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
new
species 1
new
species 1
ancestral
species
ancestral
species
transitional link
stasis
ancestral
species
new
species 2
new
species 2
Time
Time
a. Gradualistic model
b. Punctuated equilibrium 28

29. Developmental Genes and Macroevolution
Genes can bring about radical changes in body shapes and organs.
Gene Expression Can Influence Development
A change in gene expression could stop developmental process or continue it beyond its normal time.
Using modern technology researchers discovered genes whose differential expression can bring about changes in body shapes and organs. 29

30. Pax6 Gene and Eye Development
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(Left): © Carolina Biological Supply/Photo Researchers, Inc.; (Center): © Vol. OS02/PhotoDisc/Getty Images; (Right): © Aldo Brando/Peter Arnold, Inc. 30

31. Study of Pax6 Gene
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Courtesy Walter Gehring, reprinted with permission from Induction of Ectopic Eyes by Target Expression of the Eyeless Gene in Drosophila, G. Halder, P. Callaerts, Walter J. Gehring, Science Vol. 267, © 24 March 1995 American Association for the Advancement of Science 31

32. Hox6 Gene
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(Both): © A. C. Burke, 2000 32

33. Macroevolution Is Not Goal-Oriented
The evolution of the horse (Equus)
Studied since the 1870s
Model for gradual, straight-line evolution
Modern horse, had been achieved as a goal
Three trends were particularly evident during the evolution:
Increase in overall size,
Toe reduction, and
Change in tooth size and shape. 33

34. Simplified Family Tree of Equus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2 MYA
4 MYA
Equus
Neohipparion
Hipparion
12 MYA
Dinohippus
15 MYA
Megahippus
Merychippus
17 MYA
23 MYA
25 MYA
35 MYA
Miohippus
40 MYA
Palaeotherium
45 MYA
50 MYA
Hyracotherium
55 MYA 34

35. Review Separation of the Species Modes of Separation Macroevolution
Allopatic speciation
Adaptive radiation
Sympatric speciation
Macroevolution 35

36. Processes of Evolution
Biology, 9th ed,Sylvia Mader
Chapter 18
Slide #36
Processes of Evolution
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
Ensatina eschscholtzi picta 1
Members of a northern ancestral
population migrated southward.
Ensatina eschscholtzi
oregonensis
horse
mating
donkey 2
Subspecies are separated by
California’s Central Valley .Some
interbreeding between populations
does occur.
fertilization
Central
Valley
Barrier
Ensatina eschscholtzi platensis
Ensatina eschscholtzi
xanthoptica
Ensatina eschscholtzi
croceater
Usually
mules cannot
offspring
If an
reproduce.
it cannot
does result,
mule (hybrid)
Ensatina eschscholtzi
eschscholtzii
(Stallion): © Superstock, Inc.; (Donkey): © Robert J. Erwin/Photo Researchers, Inc.; (Mule): © Jorg & Petra Wegner/Animals Animals/Earth Scenes;
Offspring
Ensatina eschscholtzi
klauberi 3
Evolution has occurred, and in the south, subspecies do not interbreed even though they live in the same environment. 36