Download Species

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
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
Types of Reproductive Barriers
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY
HYBRID BREAKDOWN
Types of Reproductive Barriers
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY
HYBRID BREAKDOWN
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
Sympatric Speciation
“other” “homeland”
“together” “homeland”
Geographically isolated
populations
Overlapping populations within
home range
• Caused by geologic events
or processes
• Evolves by natural selection
& genetic drift
Gene flow between
subpopulations blocked by:
• polyploidy
• sexual selection
• habitat differentiation
Eg. Squirrels on N/S rims of
Grand Canyon
Eg. polyploidy in crops (oats,
cotton, potatoes, wheat)
Allopatric speciation of antelope squirrels
on opposite rims of the Grand Canyon
Sympatric Speciation by Polyploidy
• Autopolyploid: extra sets of chromosomes
▫ Failure of cell division (2n  4n)
2n = 6
2n
4n = 12
Autopolyploid Speciation
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
Adaptive Radiation: Hawaiian plants descended from
ancestral tarweed from North America 5 million years ago
1.3
Dubautia laxa
million
years
KAUAI
5.1
million
years
MOLOKAI
MAUI
OAHU
3.7 LANAI
million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Hybrid Zones
• Incomplete reproductive barriers
• Possible outcomes: reinforcement, fusion, stability
Grizzly
“Grolar” or
“Pizzly”
Polar
Tempo of Evolution
Gradualism
• Common ancestor
• Slow, constant change
Punctuated Equilibium
• Eldridge & Gould
• Long period of stasis
punctuated by short bursts of
significant change