Lecture AP Biology Chapter 24 The origin of species

This chapter define and discuss the limitations of the four species concepts, describe and provide examples of prezygotic and postzygotic reproductive barriers, distinguish between and provide examples of allopatric and sympatric speciation, explain how polyploidy can cause reproductive isolation, define the term hybrid zone and describe three outcomes for hybrid zones over time.

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

▫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

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:

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)

y Allopolyploid

y

•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

Foundin

g 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

N

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”

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