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