Lecture AP Biology Chapter 24 The origin of 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


HHMI Video Clip:
Reproductive Isolation and Speciation
Running Time: 2:38 min


• 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


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
“other” “homeland”

Sympatric Speciation
“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


• 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

N

1.3
million
years

Dubautia laxa
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



HHMI Short Film:
Lizards in an Evolutionary Tree
Topic: Adaptive Radiation
Running Time: 17:50 min