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Ch. 23 Warm-Up
Use the following information to help you answer the question below:
Population = 1000 people AA = 160 Aa = 480 aa = 360 1. What are the genotypic frequencies? Allele frequencies? 2. Use directional, stabilizing or disruptive selection to
answer the following: a) The mice in the Arizona desert have either dark or
light fur. b) Birds produce 4-5 eggs per clutch c) Average human baby weighs 7 lbs. d) Darwin's finches and beak size during drought
Chapter 24 The Origin of Species
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.
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
HHMI Video Clip: Reproductive Isolation
and Speciation
Running Time: 2:38 min
Biological Species Concept
• 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
Types of Reproductive Barriers
Prezygotic Barriers:
▫ Impede mating/fertilization
Types:
▫ 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
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY HYBRID BREAKDOWN
Types of Reproductive Barriers
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY HYBRID BREAKDOWN
Types of Reproductive Barriers
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
Two main modes of speciation
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)
Allopatric speciation of antelope squirrels
on opposite rims of the Grand Canyon
2n = 6 4n = 12 4n
2n
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)
Allopolyploidy
Adaptive Radiation
• 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
KAUAI 5.1
million years
OAHU 3.7
million years
HAWAII 0.4
million years
1.3 million years
MAUI MOLOKAI
LANAI Argyroxiphium sandwicense
Dubautia linearis Dubautia scabra
Dubautia waialealae
Dubautia laxa
Adaptive Radiation: Hawaiian plants descended from
ancestral tarweed from North America 5 million years ago
Hybrid Zones
• Incomplete reproductive barriers
• Possible outcomes: reinforcement, fusion, stability
“Grolar” or
“Pizzly”
Grizzly Polar
Gradualism
• Common ancestor
• Slow, constant change
Punctuated Equilibium
• Eldridge & Gould
• Long period of stasis punctuated by short bursts of significant change
Tempo of Evolution
HHMI Short Film:
Lizards in an Evolutionary Tree
Topic: Adaptive Radiation
Running Time: 17:50 min