Chapter 14 The Origin of Species - Edl · 14.1 The origin of species is the source of biological...

PowerPoint Lectures for

Campbell Biology: Concepts & Connections, Seventh Edition

Reece, Taylor, Simon, and Dickey

Chapter 14 The Origin of Species

Many species of cormorants around the world can

Cormorants on the Galápagos Islands cannot fly.

How did these flightless cormorants get to the

Galápagos Islands?

Why are these flightless cormorants found

nowhere else in the world?

Introduction

Figure 14.0_1

Defining Species Mechanisms

of Speciation

Chapter 14: Big Ideas

Figure 14.0_2

An ancestral cormorant species is thought to have

flown from the Americas to the Galápagos Islands

more than 3 million years ago.

Terrestrial mammals could not make the trip over

the wide distance, and no predatory mammals

naturally occur on these islands today.

Without predators, the environment of these

cormorants favored birds with smaller wings,

perhaps channeling resources to the production of

offspring.

Introduction

DEFINING SPECIES

14.1 The origin of species is the source of biological diversity

Microevolution is the change in the gene pool of a population from one generation to the next.

Speciation is the process by which one species splits into two or more species.

– Every time speciation occurs, the diversity of life increases.

– The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago.

Figure 14.1

14.2 There are several ways to define a species

The word species is from the Latin for “kind” or “appearance.”

Although the basic idea of species as distinct life-forms seems intuitive, devising a more formal definition is not easy and raises questions.

– How similar are members of the same species?

– What keeps one species distinct from others?

The biological species concept defines a species as

– a group of populations,

– whose members have the potential to interbreed in nature, and

– produce fertile offspring.

– Therefore, members of a species are similar because they reproduce with each other.

Reproductive isolation

– prevents members of different species from mating with each other,

– prevents gene flow between species, and

– maintains separate species.

– Therefore, species are distinct from each other because they do not share the same gene pool.

Figure 14.2A

Figure 14.2A_1

Figure 14.2A_2

Figure 14.2B

The biological species concept can be problematic.

– Some pairs of clearly distinct species occasionally interbreed and produce hybrids.

– For example, grizzly bears and polar bears may interbreed and produce hybrids called grolar bears.

– Melting sea ice may bring these two bear species together more frequently and produce more hybrids in the wild.

– Reproductive isolation cannot usually be determined for extinct organisms known only from fossils.

– Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually.

– Therefore, alternate species concepts can be useful.

Figure 14.2C

Grizzly bear Polar bear

Hybrid “grolar” bear

Figure 14.2C_1

Grizzly bear

Figure 14.2C_2

Polar bear

Figure 14.2C_3

Hybrid “grolar” bear

The morphological species concept

– classifies organisms based on observable physical traits and

– can be applied to

– asexual organisms and

– fossils.

– However, there is some subjectivity in deciding which traits to use.

The ecological species concept

– defines a species by its ecological role or niche and

– focuses on unique adaptations to particular roles in a

biological community.

– For example, two species may be similar in appearance

but distinguishable based on

– what they eat or

– where they live.

The phylogenetic species concept

– defines a species as the smallest group of individuals that

shares a common ancestor and thus

– forms one branch of the tree of life.

– Biologists trace the phylogenetic history of a species by

comparing its

– morphology or

– DNA.

– However, defining the amount of difference required to

distinguish separate species is a problem.

14.3 Reproductive barriers keep species separate

Reproductive barriers

– serve to isolate the gene pools of species and

– prevent interbreeding.

Depending on whether they function before or after zygotes form, reproductive barriers are categorized as

– prezygotic or

– postzygotic.

Figure 14.3A

Individuals of different species

Prezygotic Barriers

Habitat isolation

Temporal isolation

Behavioral isolation

Mechanical isolation

Gametic isolation

Fertilization

Postzygotic Barriers

Reduced hybrid viability

Reduced hybrid fertility

Hybrid breakdown

Viable, fertile offspring

Five types of prezygotic barriers prevent mating or

fertilization between species.

1. In habitat isolation, two species live in the same general

area but not in the same kind of place.

2. In temporal isolation, two species breed at different times

(seasons, times of day, years).

Video: Giraffe Courtship Ritual

Video: Albatross Courtship Ritual

Video: Blue-footed Boobies Courtship Ritual

Figure 14.3B

Figure 14.3B_1

Figure 14.3B_2

Figure 14.3C

Figure 14.3C_1

Figure 14.3C_2

Prezygotic Barriers, continued

3. In behavioral isolation, there is little or no mate

recognition between females and males of different

species.

4. In mechanical isolation, female and male sex organs are

not compatible.

5. In gametic isolation, female and male gametes are not

compatible.

Figure 14.3D

Figure 14.3E

Figure 14.3F

Three types of postzygotic barriers operate after

hybrid zygotes have formed.

1. In reduced hybrid viability, most hybrid offspring do not

survive.

2. In reduced hybrid fertility, hybrid offspring are vigorous

but sterile.

3. In hybrid breakdown,

– the first-generation hybrids are viable and fertile but

– the offspring of the hybrids are feeble or sterile.

Figure 14.3G

Horse Donkey

Figure 14.3G_1

Figure 14.3G_2

Donkey

Figure 14.3G_3

MECHANISMS

OF SPECIATION

14.4 In allopatric speciation, geographic isolation leads to speciation

In allopatric speciation, populations of the same

species are geographically separated, isolating their

gene pools.

Isolated populations will no longer share changes in

allele frequencies caused by

– natural selection,

– genetic drift, and/or

– mutation.

Gene flow between populations is initially prevented

by a geographic barrier. For example

– the Grand Canyon and Colorado River separate two

species of antelope squirrels, and

– the Isthmus of Panama separates 15 pairs of snapping

shrimp.

14.4 In allopatric speciation, geographic isolation leads to speciation

Figure 14.4A

South rim

A. harrisii

North rim

A. leucurus

Figure 14.4A_1

A. harrisii

Figure 14.4A_2

A. leucurus

Figure 14.4B

Isthmus of Panama

A. millsae

A. nuttingi A. formosus

A. panamensis

ATLANTIC OCEAN

PACIFIC OCEAN

14.5 Reproductive barriers can evolve as populations diverge

How do reproductive barriers arise?

Experiments have demonstrated that reproductive

barriers can evolve as a by-product of changes in

populations as they adapt to different environments.

These studies have included

– laboratory studies of fruit flies and

– field studies of monkey flowers and their pollinators.

Figure 14.5A

Starch medium Maltose medium

Initial sample

of fruit flies

Mating experiments

Female Female

Results Population

Population

#2 Starch Maltose

9 18 15

15 12 Ma

Number of matings

in experimental groups

Number of matings

in starch control groups

Figure 14.5B

Pollinator choice in

typical monkey flowers

Typical M. lewisii

(pink)

M. lewisii with

red-color allele

Typical M. cardinalis

(red) M. cardinalis with

pink-color allele

Pollinator choice after

color allele transfer

Figure 14.5B_1

Typical M. lewisii

(pink)

Figure 14.5B_2

M. lewisii with

red-color allele

Figure 14.5B_3

Typical M. cardinalis

Figure 14.5B_4

M. cardinalis with

pink-color allele

14.6 Sympatric speciation takes place without geographic isolation

Sympatric speciation occurs when a new species

arises within the same geographic area as a parent

species.

How can reproductive isolation develop when

members of sympatric populations remain in contact

with each other?

Gene flow between populations may be reduced by

– polyploidy,

– habitat differentiation, or

– sexual selection.

Many plant species have evolved by polyploidy in

which cells have more than two complete sets of

chromosomes.

Sympatric speciation can result from polyploidy

– within a species (by self-fertilization) or

– between two species (by hybridization).

14.6 Sympatric speciation takes place without geographic isolation

Figure 14.6A_s1

Parent species 2n = 6

Tetraploid cells

4n = 12

Figure 14.6A_s2

Tetraploid cells

4n = 12

Diploid gametes 2n = 6

Figure 14.6A_s3

Tetraploid cells

4n = 12

Diploid gametes 2n = 6

Viable, fertile tetraploid species 4n = 12

Self- fertilization

Figure 14.6B_s1

Species A 2n = 4

Gamete n = 2

Gamete n = 3

Species B 2n = 6

Figure 14.6B_s2

Species A 2n = 4

Gamete n = 2

Gamete n = 3

Species B 2n = 6

Chromosomes cannot pair

Can reproduce asexually

Sterile hybrid n = 5

Figure 14.6B_s3

Species A 2n = 4

Gamete n = 2

Gamete n = 3

Species B 2n = 6

Chromosomes cannot pair

Can reproduce asexually

Sterile hybrid n = 5

Viable, fertile hybrid species

2n = 10

14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation

Plant biologists estimate that 80% of all living plant species are descendants of ancestors that formed by polyploid speciation.

Hybridization between two species accounts for most of these species.

Polyploid plants include

– cotton,

– oats,

– potatoes,

– bananas,

– peanuts,

– barley,

– plums,

– apples,

– sugarcane,

– coffee, and

– bread wheat.

– has been domesticated for at least 10,000 years and

– is the most widely cultivated plant in the world.

Bread wheat, Triticum aestivum, is

– a polyploid with 42 chromosomes and

– the result of hybridization and polyploidy.

Figure 14.7_3

Figure 14.7

Domesticated

Triticum monococcum

(14 chromosomes)

DD AABB

Wild Triticum

(14 chromo-

somes)

Hybridization

Sterile hybrid (14 chromosomes)

Cell division error and self-fertilization

Hybridization

Wild T. tauschii (14 chromosomes)

T. turgidum Emmer wheat (28 chromosomes)

Cell division error

and self-fertilization

AABBDD

T. aestivum Bread wheat (42 chromosomes)

Figure 14.7_1

Domesticated

Triticum monococcum

(14 chromosomes)

DD AABB

Hybridization

2 Cell division error and self-fertilization

Wild Triticum

(14 chromo-

somes)

Figure 14.7_2

3 Hybridization

Cell division error

and self-fertilization

AABBDD

T. aestivum Bread wheat (42 chromosomes)

14.8 Isolated islands are often showcases of speciation

Most of the species on Earth are thought to have originated by allopatric speciation.

Isolated island chains offer some of the best evidence of this type of speciation.

Multiple speciation events are more likely to occur in island chains that have

– physically diverse habitats,

– islands far enough apart to permit populations to evolve in isolation, and

– islands close enough to each other to allow occasional dispersions between them.

The evolution of many diverse species from a common ancestor is adaptive radiation.

The Galápagos Archipelago

– is located about 900 km (560 miles) west of Ecuador,

– is one of the world’s great showcases of adaptive radiation,

– was formed naked from underwater volcanoes,

– was colonized gradually from other islands and the South America mainland, and

– has many species of plants and animals found nowhere else in the world.

The Galápagos islands currently have 14 species of

closely related finches, called Darwin’s finches,

because Darwin collected them during his around-

the-world voyage on the Beagle.

These finches

– share many finchlike traits,

– differ in their feeding habits and their beaks, specialized

for what they eat, and

– arose through adaptive radiation.

Figure 14.8

Cactus-seed-eater (cactus finch)

Tool-using insect-eater (woodpecker finch)

Seed-eater (medium ground finch)

Figure 14.8_1

Cactus-seed-eater (cactus finch)

Figure 14.8_2

Tool-using insect-eater (woodpecker finch)

Figure 14.8_3

Seed-eater (medium ground finch)

Peter and Rosemary Grant have worked

– for more than three decades,

– on medium ground finches, and

– on tiny, isolated, uninhabited Daphne Major in the Galápagos Islands.

14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches

Medium ground finches and cactus finches occasionally interbreed. Hybrids

– have intermediate bill sizes,

– survive well during wet years, when there are plenty of soft, small seeds around,

– are outcompeted by both parental types during dry years, and

– can introduce more genetic variation on which natural selection acts.

14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches

Figure 14.9

Larger

Smaller

Large beaks can

crack large

Severe

drought

1980 1985 1990

Smaller beaked

G. fortis can feed

on small seeds

Severe

drought

1995 2000

Competitor species,

G. magnirostris

Arrival of

new species

1975 2005

14.10 Hybrid zones provide opportunities to study reproductive isolation

What happens when separated populations of

closely related species come back into contact with

each other?

Biologists try to answer such questions by studying

hybrid zones, regions in which members of different

species meet and mate to produce at least some

hybrid offspring.

14.10 Hybrid zones provide opportunities to study reproductive isolation

Over time in hybrid zones

– reinforcement may strengthen barriers to reproduction,

such as occurs in flycatchers, or

– fusion may reverse the speciation process as gene flow

between species increases, as may be occurring among

the cichlid species in Lake Victoria.

In stable hybrid zones, a limited number of hybrid

offspring continue to be produced.

populations

of a species

Figure 14.10A

Newly formed

species

Population Barrier to

gene flow

Hybrid

individual

Hybrid

zone 1 2

Gene flow

Figure 14.10B

collared

flycatcher

Allopatric

populations

Sympatric

populations

Pied flycatcher

from allopatric

population

Pied flycatcher

from sympatric

population

Figure 14.10B_1

collared

flycatcher

Allopatric

populations

Sympatric

populations

Figure 14.10B_2

Pied flycatcher

from allopatric

population

Figure 14.10B_3

Pied flycatcher

from sympatric

population

Figure 14.10C

Pundamilia nyererei Pundamilia pundamilia

Hybrid: Pundamilia “turbid water”

14.11 Speciation can occur rapidly or slowly

There are two models for the tempo of speciation.

1. The punctuated equilibria model draws on the fossil

record, where species

– change most as they arise from an ancestral species and then

– experience relatively little change for the rest of their existence.

2. Other species appear to have evolved more gradually.

Animation: Macroevolution

Figure 14.11

Punctuated pattern

Gradual pattern

14.11 Speciation can occur rapidly or slowly

What is the total length of time between speciation

events (between formation of a species and

subsequent divergence of that species)?

– In a survey of 84 groups of plants and animals, the time

ranged from 4,000 to 40 million years.

– Overall, the time between speciation events averaged 6.5

million years.

You should now be able to

1. Distinguish between microevolution and speciation.

2. Compare the definitions, advantages, and disadvantages of the different species concepts.

3. Describe five types of prezygotic barriers and three types of postzygotic barriers that prevent populations of closely related species from interbreeding.

4. Explain how geologic processes can fragment populations and lead to speciation.

5. Explain how reproductive barriers might evolve in

isolated populations of organisms.

6. Explain how sympatric speciation can occur, noting

examples in plants and animals.

7. Explain why polyploidy is important to modern

agriculture.

8. Explain how modern wheat evolved.

9. Describe the circumstances that led to the adaptive

radiation of the Galápagos finches.

10. Describe the discoveries made by Peter and

Rosemary Grant in their work with Galápagos

finches.

11. Explain how hybrid zones are useful in the study

of reproductive isolation.

12. Compare the gradual model and the punctuated

equilibrium model of evolution.

Figure 14.UN01

Zygote

Gametes Prezygotic barriers Postzygotic barriers

Viable,

fertile

offspring • Habitat isolation

• Temporal isolation

• Behavioral isolation

• Mechanical isolation

• Gametic isolation

• Reduced hybrid

viability

• Reduced hybrid

fertility

• Hybrid breakdown

Figure 14.UN02

Original population

Figure 14.UN03

Species

may interbreed in a

b. c. d.

outcome may be

reproductive barriers

a few hybrids

continue to be produced

species separate

speciation is reversed

keeps and

Figure 14.UN03_1

Species

may interbreed in a

b. c. d.

outcome may be

Figure 14.UN03_2

b. c. d.

reproductive barriers

a few hybrids

continue to be produced

species separate

speciation is reversed

keeps and

Figure 14.10UN

Fusion Reinforcement Stability

Figure 14.10UN_1

Reinforcement

Figure 14.10UN_2

Fusion

Figure 14.10UN_3

Stability

Chapter 14 The Origin of Species - Edl · 14.1 The origin of species is the source of biological...

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