Chapter 22
description
Transcript of Chapter 22
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Chapter 22The Origin of Species
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What You Need to Know:• The difference between microevolution and
macroevolution.• The biological concept of a species.• Prezygotic and postzygotic barriers that
maintain reproductive isolation in natural populaitons.
• How allopatric and sympatric speciation are similar and different.
• How autopolyploid or an allopolyploid chromosomal change can lead to sympatric speciation.
• How punctuated equilibrium and gradualism describe two different tempos of speciation.
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Speciation = origin of species
•Microevolution: changes within a single gene pool
•Macroevolution: evolutionary change above the species level▫cumulative effects of speciation over long
periods of time
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•Species = population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring▫Reproductively compatible
•Reproductive isolation = barriers that prevent members of 2 species from producing viable, fertile hybrids
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Prezygotic Barriers:▫Impede
mating/fertilizationTypes:
▫Habitat isolation▫Temporal isolation▫Behavioral isolation▫Mechanical
isolation▫Gametic isolation
Postzygotic Barriers:▫Prevent hybrid
zygote from developing into viable adult
Types:▫Reduced hybrid
viability▫Reduced hybrid
fertility▫Hybrid breakdown
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REDUCED HYBRIDVIABILITY
REDUCED HYBRIDFERTILITY
HYBRID BREAKDOWN
Types of Reproductive Barriers
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REDUCED HYBRIDVIABILITY
REDUCED HYBRIDFERTILITY
HYBRID BREAKDOWN
Types of Reproductive Barriers
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Other definitions of species:
•Morphological – by body shape, size, and other structural features
•Ecological – niche/role in community
•Phylogenetic – share common ancestry, branch on tree of life
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Two main modes of speciation
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Two main modes of speciation:Allopatric Speciation
“other” “homeland”
Geographically isolated populations
• Caused by geologic events or processes
• Evolves by natural selection & genetic drift
Eg. Squirrels on N/S rims of Grand Canyon
Sympatric Speciation
“together” “homeland”
Overlapping populations within home range
Gene flow between subpopulations blocked by:
• polyploidy• sexual selection• habitat differentiation
Eg. polyploidy in crops (oats, cotton, potatoes, wheat)
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Allopatric speciation of antelope squirrels on opposite rims of the Grand
Canyon
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2n = 6 4n = 12 4n2n
Autopolyploid Speciation
Sympatric Speciation by Polyploidy•Autopolyploid: extra sets of chromosomes
▫Failure of cell division (2n 4n)
▫Eg. Strawberries are 4n, 6n, 8n, 10n (decaploid)!
•Allopolyploid: 2 species produce a hybrid▫Species A (2n=6) + Species B (2n=4)
Hybrid (2n=10)
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Allopolyploidy
Allopolyploidy
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•Many new species arise from a single common ancestor
•Occurs when: A few organisms make way to new,
distant areas (allopatric speciation) Environmental change extinctions
new niches for survivors•Eg. Hawaiian archepelago
Founding
Parents
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KAUAI5.1
millionyears OAHU
3.7millionyears
HAWAII0.4
millionyears
1.3millionyears
MAUIMOLOKAI
LANAI Argyroxiphium sandwicense
Dubautia linearisDubautia scabra
Dubautia waialealae
Dubautia laxa
N
Adaptive Radiation: Hawaiian plants descended from ancestral tarweed from North America 5 million years ago
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Hybrid Zones• Incomplete reproductive barriers•Possible outcomes: reinforcement, fusion, stability
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“Grolar” or “Pizzly”
Grizzly Polar
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Gradualism• Common ancestor• Slow, constant
change
Punctuated Equilibium• Eldridge & Gould• Long period of stasis
punctuated by short bursts of significant change
Tempo of Evolution
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