Chapter 14jfalabella.weebly.com/.../2/5/2/4/25249222/14_lecture_presentation.pdf · Chapter 14...

© 2015 Pearson Education, Inc.

PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE • TAYLOR • SIMON • DICKEY • HOGAN

Chapter 14

Lecture by Edward J. Zalisko

The Origin of Species


Introduction

• Bowerbirds, native to New Guinea and Australia, are named for the structure, called a bower, that the male weaves from twigs and grasses to attract females.

• After building his bower, the male collects objects such as fruits, seeds, insect parts, rocks, flowers, and leaves and arranges them artfully by color and type.


Figure 14.0-1


Figure 14.0-2

Chapter 14: Big Ideas

Defining Species Mechanisms of Speciation


Introduction

• Females •  tour the bowers of local males, inspecting each

bower carefully while its owner courts her with a song and dance, and

• may visit promising candidates multiple times before finally mating with one.


Introduction

• Not all Vogelkop bowerbirds construct displays like the one in the photo.

• The males of another population build a simpler structure consisting of sticks loosely woven around a central sapling.

• Researchers hypothesize that this divergence in display preferences has started the two populations on separate evolutionary paths, with each path leading to a new species, or speciation.


Introduction

• 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.


DEFINING SPECIES


14.1 The origin of species is the source of biological diversity

• Darwin was eager to explore landforms newly emerged from the sea when he came to the Galápagos Islands.

• He noted that these volcanic islands, despite their geologic youth, were teeming with plants and animals found nowhere else in the world.

• He realized that these species, like the islands, were relatively new.



• 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.

• Each time speciation occurs, the diversity of life increases.


Figure 14.1



• Over the course of 3.5 billion years, •  an ancestral species first gave rise to two or more

different species, • which then branched to new lineages, • which branched again, •  until we arrive at the millions of species that live, or

once lived, on Earth.


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.

•  In many cases, the differences between two species are obvious. In other cases, the differences between two species are not so obvious.


Figure 14.2a-0


Figure 14.2a-1


Figure 14.2a-2


14.2 There are several ways to define a species • How similar are members of the same species?

• Whereas the individuals of many species exhibit fairly limited variation in physical appearance, certain other species—our own, for example—seem extremely varied.


Figure 14.2b


14.2 There are several ways to define a species • 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 (offspring that themselves can reproduce).

• Thus, members of a biological species are united by being reproductively compatible, at least potentially.


14.2 There are several ways to define a species • Reproductive isolation

•  prevents genetic exchange (gene flow) and • maintains a boundary between species.

• But there are some pairs of clearly distinct species that do occasionally interbreed.

•  The resulting offspring are called hybrids. •  An example is the grizzly bear (Ursus arctos) and

the polar bear (Ursus maritimus), whose hybrid offspring have been called “grolar bears.”


Figure 14.2c-0

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


14.2 There are several ways to define a species • There are other instances in which applying the

biological species concept is problematic. •  There is no way to determine whether organisms

that are now known only through fossils were once able to interbreed.

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

•  Therefore, alternate species concepts can be useful.


14.2 There are several ways to define a species • 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.


14.2 There are several ways to define a species • The ecological species concept

•  defines a species by its ecological 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 the depth of water in which they are usually found.


14.2 There are several ways to define a species •  The phylogenetic species concept defines a species

as the smallest group of individuals that share a common ancestor and thus form one branch of the tree of life.

•  Biologists trace the phylogenetic history of a species by comparing its

•  morphology, •  DNA sequences, or •  biochemical pathways.

• However, agreeing on the amount of difference required to establish separate species remains a challenge.


14.3 VISUALIZING THE CONCEPT: 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.


14.3 VISUALIZING THE CONCEPT: Reproductive barriers keep species separate • Five types of prezygotic barriers prevent mating

or fertilization between species. 1.  In habitat isolation, there is a lack of opportunity

for mates to encounter each other. 2.  In temporal isolation, there is breeding at different

times or seasons.


Figure 14.3-0

Habitat isolation (different habitats)

Temporal isolation (breeding at different times)

Behavioral isolation (different courtship rituals)

Mechanical isolation (incompatible reproductive parts)

Gametic isolation (incompatible gametes)

Reduced hybrid vitality (short-lived hybrids)

Reduced hybrid fertility (sterile hybrids)

Hybrid breakdown (fertile hybrids with

sterile offspring)

PREZYGOTIC BARRIERS

POSTZYGOTIC BARRIERS


Figure 14.3-1

Habitat isolation (lack of opportunities to encounter each other)

The garter snake Thamnophis atratus lives mainly in water.

The garter snake Thamnophis sirtalis lives on land.


Figure 14.3-9


Figure 14.3-10


Figure 14.3-2

Temporal isolation (breeding at different times or seasons)

The eastern spotted skunk (Spilogale putorius) breeds in late winter. The western spotted skunk

(Spilogale gracilis) breeds in the fall.


Figure 14.3-11


Figure 14.3-12


14.3 VISUALIZING THE CONCEPT: Reproductive barriers keep species separate

3.  In behavioral isolation, there is failure to send or receive appropriate signals.

4.  In mechanical isolation, there is physical incompatibility of reproductive parts.

5.  In gametic isolation, there is molecular incompatibility of eggs and sperm or pollen and stigma.


Video: Blue-Footed Boobies Courtship Ritual


Video: Albatross Courtship Ritual


Video: Giraffe Courtship Ritual


Figure 14.3-3

Behavioral isolation (different courtship rituals)

The blue-footed booby (Sula nebouxii) performs an elaborate courtship dance.

The masked booby (Sula dactylatra) performs a different courtship ritual.


Figure 14.3-13


Figure 14.3-14


Figure 14.3-4

Mechanical isolation (physical incompatibility of reproductive parts)

Heliconia pogonantha is pollinated by hummingbirds with long, curved bills.

Heliconia latispatha is pollinated by hummingbirds with short, straight bills.


Figure 14.3-15


Figure 14.3-16


Figure 14.3-5

Gametic isolation (molecular incompatibility of eggs and sperm

or pollen and stigma)

Purple sea urchin (Strongylocentrotus purpuratus)

Red sea urchin (Strongylocentrotus franciscanus)


Figure 14.3-17


Figure 14.3-18


14.3 VISUALIZING THE CONCEPT: Reproductive barriers keep species separate • Three types of postzygotic barriers operate after

hybrid zygotes have formed. 1.  In reduced hybrid viability, interaction of parental

genes impairs the hybrid’s development or survival.

2.  In reduced hybrid fertility, hybrids are vigorous but cannot produce viable offspring.

3.  In hybrid breakdown, hybrids are viable and fertile, but their offspring are feeble or sterile.


Figure 14.3-6

Reduced hybrid viability (hybrid development or survival impaired

by interaction of parental genes)

Some salamander species can hybridize, but their offspring do not develop fully or are frail and will not survive long enough to reproduce.


Figure 14.3-19


Figure 14.3-7

Reduced hybrid fertility (vigorous hybrids that cannot

produce viable offspring)

A mule is the sterile hybrid offspring of a horse and a donkey.


Figure 14.3-20


Figure 14.3-8

Hybrid breakdown (viable and fertile hybrids with feeble

or sterile offspring)

The rice hybrids on the left and right are fertile, but plants of the next generation (middle) are sterile.


Figure 14.3-21


MECHANISMS OF SPECIATION


14.4 In allopatric speciation, geographic isolation leads to speciation

• A key event in the origin of a new species is the separation of a population from other populations of the same species.

• With its gene pool isolated, the splinter population can follow its own evolutionary course.

• Changes in allele frequencies caused by natural selection, genetic drift, and mutation will not be diluted by alleles entering from other populations (gene flow).



•  In allopatric speciation, the initial block to gene flow may come from a geographic barrier that isolates a population.



• Several geologic processes can isolate populations.

•  A mountain range may emerge and gradually split a population of organisms that can inhabit only lowlands.

•  A large lake may subside until there are several smaller lakes, isolating certain fish populations.

• Continents themselves can split and move apart. •  Allopatric speciation can also occur when

individuals colonize a remote area and become geographically isolated from the parent population.



• How large must a geographic barrier be to keep allopatric populations apart?

•  The answer depends on the ability of the organisms to move.

•  Birds, mountain lions, and coyotes can easily cross mountain ranges.

•  In contrast, small rodents may find a canyon or a wide river a formidable barrier. The Grand Canyon and Colorado River separate two species of antelope squirrels.


Figure 14.4a-0

South rim North rim

A. harrisii A. leucurus


Figure 14.4a-1

A. harrisii


Figure 14.4a-2

A. leucurus



•  Thirty species of snapping shrimp in the genus Alpheus live off the Isthmus of Panama, the land bridge that connects South and North America.

•  Morphological and genetic data group these shrimp into 15 pairs of species, with the members of each pair being each other’s closest relative.

•  In each case, one member of the pair lives on the Atlantic side of the isthmus, while the other lives on the Pacific side.

•  This strongly suggests that geographic separation of the ancestral species of these snapping shrimp led to allopatric speciation.


Figure 14.4b

A. panamensis

A. nuttingi A. formosus

A. millsae

Isthmus of Panama

ATLANTIC OCEAN

PACIFIC OCEAN


14.5 Reproductive barriers can evolve as populations diverge

• How do reproductive barriers arise? • The environment of an isolated population may

include •  different food sources, •  different types of pollinators, and •  different predators.

• As a result of natural selection acting on preexisting variations (or as a result of genetic drift or mutation), a population’s traits may change in ways that also establish reproductive barriers.


14.5 Reproductive barriers can evolve as populations diverge

• Researchers have successfully documented the evolution of reproductive isolation with laboratory experiments.

• 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

Number of matings in experimental groups

Mating experiments

Female Results Starch

Number of matings In starch control groups

Female

Maltose Population

#1 Population

#2

Mal

e Star

ch

Mal

tose

Mal

e Po

p#2

Pop#

1

22

8

9

20

18

12

15

15


Figure 14.5b-0 Pollinator choice in typical monkey flowers

Pollinator choice after color allele transfer

Typical M. lewisii (pink)

M. lewisii with red-color allele

Typical M. cardinalis (red)

M. cardinalis with pink-color allele


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 (red)


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 its 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 originated from sympatric speciation that occurs when accidents during cell division result in extra sets of chromosomes.

• New species formed in this way are polyploid, in that their 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).


Figure 14.6a-1

Parent species 2n = 6

Tetraploid cells

4n = 12

1


Figure 14.6a-2


Tetraploid cells

4n = 12 Diploid

gametes 2n = 6

1 2

3


Figure 14.6a-3

Self- fertilization


Tetraploid cells

4n = 12 Diploid

gametes 2n = 6

Viable, fertile tetraploid species 4n = 12

1 2

3


Figure 14.6b-1

Species A 2n = 4

Species B 2n = 6

Gamete n = 2

Gamete n = 3


Figure 14.6b-2

Species A 2n = 4 1

2 Species B 2n = 6

Gamete n = 2

Chromosomes cannot pair

Gamete n = 3

Sterile hybrid n = 5

Can reproduce asexually


Figure 14.6b-3

Species A 2n = 4 1

2

3

Species B 2n = 6

Gamete n = 2

Chromosomes cannot pair

Gamete n = 3

Sterile hybrid n = 5

Can reproduce asexually

Viable, fertile hybrid species

2n = 10


14.7 EVOLUTION CONNECTION: The origin of most plant species can be traced 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, perhaps because of the adaptive advantage of the diverse genes a hybrid inherits from different parental species.



• Polyploid plants include •  cotton, •  oats, •  potatoes, •  bananas, •  peanuts, •  barley,

•  plums, •  apples, •  sugarcane, •  coffee, and • wheat.


Figure 14.7-3



• 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 14.7-0

Wild Triticum (14 chromosomes)

Domesticated Triticum monococcum (14 chromosomes)

Sterile hybrid (14 chromosomes)

T. turgidum Emmer wheat (28 chromosomes)

Wild T. tauschii (14 chromosomes)

T. aestivum Bread wheat (42 chromosomes)


1

2

3

4

Hybridization

Cell division error and self-fertilization

Hybridization


AA BB

AABB

AB

DD

ABD

AABBDD


Figure 14.7-1

1

2

Wild Triticum (14 chromosomes)

Domesticated Triticum monococcum (14 chromosomes)




Hybridization


AA BB

AABB

AB

DD


Figure 14.7-2

3

4

Hybridization




T. aestivum Bread wheat (42 chromosomes)


ABD

AABBDD

AABB DD


14.8 Isolated islands are often showcases of speciation

•  Isolated island chains are often inhabited by unique collections of species.

•  Islands that have physically diverse habitats and that are far enough apart to permit populations to evolve in isolation but close enough to allow occasional dispersions to occur are often the sites of multiple speciation events.

• The evolution of many diverse species from a common ancestor is known as 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 from

5 million to 1 million years ago, • 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 birds •  share many finchlike traits, •  differ in their feeding habits and their beaks,

specialized for what they eat, and •  arose through adaptive radiation.


Figure 14.8-0

Cactus-seed-eater (cactus finch)

Tool-using insect-eater (woodpecker finch)

Seed-eater (large 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 (large ground finch)


14.9 SCIENTIFIC THINKING: Lake Victoria is a living laboratory for studying speciation

• We can see speciation occurring. • The species living today represent a snapshot, a

brief instant in this vast span of time. • The environment continues to change, sometimes

rapidly due to human impact, and natural selection continues to act on affected populations.

• Researchers have documented at least two dozen cases in which populations are diverging as they exploit different food resources or breed in different habitats.



• Sexual selection is a form of natural selection in which individuals with certain traits are more likely to obtain mates.

•  In addition to the bowerbirds already discussed, biologists have identified several other animal populations that are diverging as a result of differences in how males attract females or how females choose mates.



•  Biologists can also test hypotheses about the process of speciation by studying species that arose recently.

• Cichlids are a family of fishes that live in tropical lakes and rivers.

•  They come in all colors of the rainbow. •  They are renowned for the spectacular adaptive

radiations that stocked the large lakes of East Africa with more than a thousand species of cichlids in less than 100,000 years.

•  In the largest of these lakes, Lake Victoria, roughly 500 species evolved in about 15,000 years.


Figure 14.9a

Uganda Kenya

Lake Victoria

Tanzania

Indian Ocean



•  In Lake Victoria, there are pairs of closely related cichlid species that differ in color but nothing else.

•  Breeding males of Pundamilia nyererei have a bright red back and dorsal fin.

•  Breeding males of Pundamilia pundamilia males are metallic blue-gray.


Figure 14.9b

Pundamilia nyererei

Pundamilia pundamilia



•  Pundamilia females prefer brightly colored males. • Mate-choice experiments performed in the laboratory

showed that •  P. nyererei females prefer red males over blue males, •  P. pundamilia females prefer blue males over red males, •  the vision of P. nyererei females is more sensitive to red

light than blue light, and •  the vision of P. pundamilia females is more sensitive to

blue light than red light.

• Researchers also demonstrated that this color sensitivity is heritable.



• As light travels through water, suspended particles selectively absorb and scatter the shorter (blue) wavelengths, so light becomes increasingly red with increasing depth.

• Thus, in deeper waters, P. nyererei males are pleasingly apparent to females with red-sensitive vision but virtually invisible to P. pundamilia females.



• When biologists sampled cichlid populations in Lake Victoria, they found that

•  P. nyererei breeds in deep water, while •  P. pundamilia inhabits shallower habitats where the

blue males shine brightly. • As a consequence of their mating behavior, the two

species encounter different environments that may result in further divergence.


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.

• Figure 14.10A illustrates the formation of a hybrid zone, starting with the ancestral species.


Figure 14.10a

Population Gene flow

Barrier to gene flow

Gene flow

Hybrid individual

Hybrid zone

Newly formed species

Three populations of a species

4

3

2 1



• Reinforcement • When hybrid offspring are less fit than members of

both parent species, we might expect •  natural selection to strengthen, or reinforce,

reproductive barriers, thus reducing the formation of unfit hybrids, and

•  that barriers between species should be stronger where the species overlap (that is, where the species are sympatric).

•  The closely related collared flycatcher and pied flycatcher are an example of reinforcement.


Figure 14.10b-0 Allopatric populations

Sympatric populations

Male collared flycatcher

Male pied flycatcher

Pied flycatcher from allopatric population

Pied flycatcher from sympatric population


Figure 14.10b-1

Allopatric populations

Sympatric populations

Male collared flycatcher

Male pied flycatcher


Figure 14.10b-2

Pied flycatcher from allopatric population


Figure 14.10b-3

Pied flycatcher from sympatric population



• Fusion • What happens when the reproductive barriers

between species are not strong and the species come into contact in a hybrid zone?

•  So much gene flow may occur that the speciation process reverses, causing the two hybridizing species to fuse into one.

•  Such a situation has been occurring among the cichlid species in Lake Victoria.



• Pollution caused by development along the shores of Lake Victoria has turned the water murky.

• What happens when P. nyererei or P. pundamilia females can’t tell red males from blue males?

•  The behavioral barrier crumbles. • Many viable hybrid offspring are produced by

interbreeding. •  The once isolated gene pools of the parent species

are combining, with two species fusing into a single hybrid species.


Figure 14.10c

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 change relatively little for the rest of their existence.

2.  Other species appear to have evolved more gradually.

• The time interval between speciation events varies from a few thousand years to tens of millions of years.


Animation: Macroevolution


Figure 14.11

Punctuated pattern

Gradual pattern

Time


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.  Explain how new species of fish have evolved in Lake Victoria.

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

Reinforcement


Figure 14.UN02

Fusion


Figure 14.UN03

Stability


Figure 14.UN04

Reinforcement Fusion Stability


Figure 14.UN05

Zygote

Gametes Viable, fertile

offspring Prezygotic barriers •  Habitat isolation •  Temporal isolation •  Behavioral isolation •  Mechanical isolation •  Gametic isolation

Postzygotic barriers •  Reduced hybrid

viability •  Reduced hybrid

fertility •  Hybrid breakdown


Figure 14.UN06

Original population

a. b.


Figure 14.UN07

Species

reproductive barriers

a few hybrids

continue to be produced

species seperate

speciation is reversed

a.

b. c. d.

e. f.

may interbreed in a

outcome may be

when

are

keeps and

when when

are

Chapter 14jfalabella.weebly.com/.../2/5/2/4/25249222/14_lecture_presentation.pdf · Chapter 14...

Documents

Transcript of Chapter 14jfalabella.weebly.com/.../2/5/2/4/25249222/14_lecture_presentation.pdf · Chapter 14...