Biology Sylvia S. Mader Michael Windelspecht Chapter 17 Speciation and Macroevolution Lecture...

BiologySylvia S. Mader

Michael Windelspecht

Chapter 17Speciation and MacroevolutionLecture Outline

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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17.1 How New Species Evolve• Macroevolution is best observed within

the fossil record Requires the origin of species, also called

speciation. Speciation is the final result of changes in

the gene pool’s allelic and genotypic frequencies.

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How New Species Evolve

• Every species has its own evolutionary history

• Species Concepts Refers to the different ways in which a

species is defined.

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• Morphological species concept Based on analysis of diagnostic traits

distinguishing one species from another.• Can be distinguished anatomically• Method used by Linnaeus• Most species are described this way

4

How New Species Evolve• The evolutionary species concept

distinguishes species from one another based on morphological (structural) traits Critical traits for distinguishing species are

called diagnostic traits

• The phylogenetic species concept relies on the identification of species based on common ancestry. A common ancestor for two or more

different groups. 5

Evolutionary

Species Concept

6


Orcinus orca

Rodhocetus kasrani

Ambulocetus natans

Pakicetus attocki

Hindlimbs tooreduced for walkingor swimming

Hindlimbs usedfor both walkingon land andpaddling in water

Tetrapod with limbsfor walking


• Biological Species Concept• Populations of the same species breed only

among themselves• Experience reproductive isolation from other

such populations• Very few species are actually tested for

reproductive isolation

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• Reproductive isolating mechanisms inhibit gene flow between species

• Two general types: (1) Prezygotic Isolating Mechanisms – prevent

mating attempts or make it unlikely that fertilization will be successful

• Habitat Isolation - species occupy different habitats• Temporal Isolation - each reproduces at a different time • Behavioral Isolation - courtship patterns for recognizing

mates• Mechanical Isolation - incompatible animal genitalia or plant

floral structures• Gamete Isolation - gametes that meet do not fuse to

become a zygote

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Reproductive Barriers

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MatingPremating

Postzygotic Isolating MechanismsPrezygotic Isolating Mechanisms

Fertilization

species 1

species 2

Habitat isolationSpecies at same localeoccupy different habitats.

Temporal isolationSpecies reproduce atdifferent seasons ordifferent times of day.

Behavioral isolationIn animal species,courtship behavior differs,or individuals respond todifferent songs, calls,pheromones, or othersignals.

Gamete isolationSperm cannot reachor fertilize egg.

Mechanical isolationGenitalia betweenspecies are unsuitablefor one another.

Zygote mortalityFertilization occurs, butzygote does not survive.

Hybrid sterilityHybrid survives but is sterile and cannotreproduce.

F2 fitnessHybrid is fertile, but F2 hybridhas reduced fitness.

hybridoffspring

Temporal Isolation

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woo

d fr

ogle

opar

d fr

ogpi

cker

el fr

og

gree

n fr

og

bullf

rog

high

low

Ma

tin

g A

ctiv

ity

March 1 April 1 May 1 June 1 July 1

Prezygotic Isolating Mechanism

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© Barbara Gerlach/Visuals Unlimited


• Reproductive Isolating Mechanisms (cont.)

Postzygotic Isolating Mechanisms - Prevent hybrid offspring from developing or breeding

• Hybrid Inviability - hybrid zygote is not viable and dies

• Hybrid Sterility - hybrid zygote develops into a sterile adult

12

Postzygotic Isolating Mechanism

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top left: © Creatas/PunchStock RF; top right: © Photodisc Collection/Getty RF; bottom : © Jorg & Petra Wegner/Animals Animals

horse

mating

fertilization

mule(hybrid)mule(hybrid)

Usually mules cannot reproduce (are sterile).If mules doproduce an offspring,it usually is sterile.

Offspring

donkey

Parents

17.2 Modes of Speciation

• Speciation: 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

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Allopatric Speciation

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Ensatina eschscholtzi picta

Ensatina eschscholtzi platensis

1

2

3

Members of a northern ancestral population migrated southward.

Ensatina eschscholtzioregonensis

Subspecies are separated by California’s Central Valley .Some interbreeding between populations does occur.

Ensatina eschscholtzixanthoptica Ensatina eschscholtzi

croceater

Ensatina eschscholtzieschscholtzii

Ensatina eschscholtziklauberi

Evolution has occurred, and in the south, subspecies do not interbreed even though they live in the same environment.

CentralValleyBarrier

Allopatric Speciation Among Sockeye Salmon

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Lake female

Lake male River male

River female

a. Sockeye salmon at Pleasure Point Beach, Lake Washington b. Sockeye salmon in Cedar River .The river connects with Lake Washington.

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Modes of Speciation

• Two modes (continued): (2) Sympatric Speciation

• One population develops into two or more reproductively isolated groups

• No prior geographic isolation• In plants, sympatric speciation often involves

polyploidy (a chromosome number beyond the diploid [2n] number)

– Tetraploid hybridization in plants» Results in self fertile species that are reproductively

isolated from either parental species

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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.

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Autoploidy

Clarkia concinna Clarkia virgata

hybrid

2n = 14 2n = 10

2n = 24

doubling of chromosome number

Clarkia pulchella (C. pulchella): © J. L. Reveal; (C. concinna): © Gerald & Buff Corsi/Visuals Unlimited; (C. virgata): ©: Dr. Dean Wm. Taylor/Jepson Herbarium, UC Berkeley


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Modes of Speciation

• Adaptive Radiation

Occurs 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

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Adaptive Radiation in Hawaiian Honeycreepers


Amakihi

Akepa

Akiapolaau

Nukupuu

*Akialoa

* Extinct species or subspecies

Maui parrot bill

Palila

Ou

* Lesser Koa finch

Laysanfinch

* Greater Koa finch

* Kona finch

* Kauai akialoa

Alauwahio(Hawaiiancreeper)

Anianiau(lesseramakihi)

Greatamakihi(greensolitaire)

Genus Psittirostra

Genus Loxops

Genus Hemignathus

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Modes of Speciation

• Convergent Evolution

Occurs when a similar biological trait evolves in two unrelated species as a result of exposure to similar environments.

• Traits evolving in this manner are termed analogous traits.

– Similar function, but different origin

– Ex: bird wing vs. bat wing

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Convergent Evolution of Africa Lake Fish


Lake Tanganyika

Lake Malawi

Lake MalawiLake TanganyikaReprinted by permission from Macmillan Publishers Ltd on behalf of Cancer Research UK: RC Albertson, TD Kocher (2006) Genetic and developmental basis of cichlid trophic diversity. Heredity vol. 97 (3) pp. 211-221

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17.3 Principles of Macroevolution

• Macroevolution Evolution at the species or higher level of

classification Some evolutionists support a gradualistic

model• Evolution at the species level occurs gradually• Speciation occurs after populations become isolated • Each group continues its own evolutionary pathway • The gradualistic model suggests that it is difficult to

indicate when speciation occurred

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Principles of Macroevolution

• Macroevolution Some paleontologists support the punctuated

equilibrium model• Species can appear quite suddenly

– Species then remain essentially unchanged phenotypically during a period of stasis (sameness) until they undergo extinction.

• This model states that periods of equilibrium are punctuated by speciation

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Gradualistic and Punctuated Equilibrium Models


transitional link

a. Gradualistic model b. Punctuated equilibrium

stasis

newspecies 1

newspecies 1

ancestralspecies

ancestralspecies

ancestralspecies

newspecies 2

newspecies 2

Time Time

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• 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 a 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.

– Pax6 in eye development– Tbx5 in limb development– Hox genes in development of overall shape

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Pax6 Gene and Eye Development


(Left): © Carolina Biological Supply/Photo Researchers, Inc.; (Center): © Vol. OS02/PhotoDisc/Getty Images; (Right): © Aldo Brando/Peter Arnold, Inc.

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Study of Pax6 Gene

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


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Hox6 GenesCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(Both): © A. C. Burke, 2000

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• Macroevolution is not goal-oriented The evolution of the horse (Equus)

• Studied since the 1870s • Model for gradual, straight-line evolution with the

modern-horse as its goal• Three trends were particularly evident during the

evolution of the horse:– Increase in overall size– Toe reduction– Change in tooth size and shape

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• Macroevolution is not goal-oriented Discovery of more fossils has led to recognition

that:• The lineage of a horse is complicated by the

presence of many ancestors with varied traits– The direct ancestor of Equus is not known– Each ancestral species was adapted to its

environment• Speciation, diversification, and extinction are

common occurrences in the fossil record

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Simplified Family Tree of EquusCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 MYA

4 MYA

12 MYA

15 MYA

17 MYA

23 MYA

25 MYA

35 MYA

40 MYA

45 MYA

50 MYA

55 MYA

Equus

Dinohippus

NeohipparionHipparion

Megahippus

Miohippus

Palaeotherium

Hyracotherium

Merychippus

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Biology Sylvia S. Mader Michael Windelspecht Chapter 17 Speciation and Macroevolution Lecture...

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