biology sylvia s. mader michael windelspecht chapter 17 speciation and macroevolution lecture...
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BiologySylvia S. Mader
Michael Windelspecht
Chapter 17Speciation and MacroevolutionLecture Outline
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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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How New Species Evolve
• 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
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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
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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
How New Species Evolve
• 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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How New Species Evolve
• 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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ogle
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el fr
og
gree
n fr
og
bullf
rog
high
low
Ma
tin
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March 1 April 1 May 1 June 1 July 1
Prezygotic Isolating Mechanism
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© Barbara Gerlach/Visuals Unlimited
How New Species Evolve
• 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
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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
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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
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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
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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
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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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Principles of Macroevolution
• 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
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(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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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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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Principles of Macroevolution
• 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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Principles of Macroevolution
• 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