chapter 14 the origin of species - napa valley college 110/14...initial sample starch medium of...

Copyright © 2009 Pearson Education, Inc.

PowerPoint Lectures for

Biology: Concepts & Connections, Sixth Edition

Campbell, Reece, Taylor, Simon, and Dickey

Chapter 14 The Origin of Species

Lecture by Joan Sharp

Until recently, over 500 species of cichlid fishes lived in East Africa’s Lake Victoria

– Where did these species come from?

– Why are they disappearing?


Introduction: The Rise and Fall of Cichlids

LakeTanganyika

Africa

Tanzania

KenyaUganda

LakeVictoria

LakeMalawi

Lake Victoria’s cichlids diversified 100,000 years ago

– Different species of cichlid have specialized mouthparts that allow them to specialize on different food sources

– The bright colors of the males vary with species, as females chose males with specific colors

Groups isolated by diet or female mate choice may have lost the ability to interbreed




A species can be defined as a group of organisms whose members can breed and produce fertile offspring, but who do not produce fertile offspring with members of other groups



Two closely related species of cichlid, Pundamilia nyererei and Pundamilia pundamilia, feed at different depths

The males of the two species differ in color


Pundamilia nyererei Pundamilia pundamilia


Females of each species prefer brightly colored males with the ―right‖ color

How do females benefit from this choice?



Over the last 30 years, 200 species of cichlids have disappeared from Lake Victoria

– Some were eaten by the Nile perch, an introduced predator

In the polluted waters of Lake Victoria, it is more difficult for females to choose brightly colored males of the right species

– As a result, the gene pools of separate species are mixing, as two species fuse back into one



14.1 The origin of species is the source of biological diversity

Speciation is the emergence of new 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 3.6 billion years ago


CONCEPTS OF SPECIES


14.2 There are several ways to define a species

Taxonomy is the branch of biology that names and classifies species and groups them into broader categories

Carolus Linnaeus developed the binomial system of naming organisms using physical characteristics to distinguish over 11,000 species

Similarities between some species and variation within species can make defining species difficult


The biological species concept defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce fertile offspring

Reproductive isolation prevents gene flow and maintains separate species



Can the biological species concept always distinguish species from each other?



The morphological species concept classifies organisms based on observable phenotypic traits

It can be applied to asexual organisms, fossils, and in cases when we donít know about possible interbreeding

There is some subjectivity in deciding which traits to use



The ecological species concept defines a species by its ecological role or niche

– Consider the cichlids, which are similar in appearance but feed at different depths in the lake



The phylogenetic species concept defines a species as a set of organisms representing a specific evolutionary lineage

– Morphological or DNA similarities or differences can be used to define a species

– 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 a species gene pool and prevent interbreeding

Reproductive barriers are categorized as prezygotic or postzygotic, depending on whether they function before or after zygotes form

Prezygotic Barriers

– Prezygotic barriers prevent mating or fertilization between species

– In temporal isolation, two species breed at different times (seasons, times of day, years)

– In habitat isolation, two species live in the same general area but not in the same kind of place


Video: Blue-footed Boobies Courtship Ritual

Video: Albatross Courtship Ritual

Video: Giraffe Courtship Ritual


14_03BBoobiesCourtship_SV.mpg

14_03BAlbatrossCourtship_SV.mpg

14_03BGiraffeCourtship_SV.mpg


Prezygotic Barriers

– In behavioral isolation, there is little or no sexual attraction between species, due to specific behaviors

– In mechanical isolation, female and male sex organs are not compatible

– In gametic isolation, female and male gametes are not compatible



Postzygotic Barriers

– Postzygotic barriers operate after hybrid zygotes are formed

– In reduced hybrid viability, most hybrid offspring do not survive

– In reduced hybrid fertility, hybrid offspring are vigorous but sterile

– In hybrid breakdown, the first-generation hybrids are viable and fertile, but the offspring of the hybrids are feeble or sterile

– The process of speciation depends on whether reproductive barriers prevent gene flow between populations



If two related species live in the same area, would natural selection favor the evolution of prezygotic or postzygotic reproductive isolating mechanisms?



MECHANISMS OF SPECIATION


14.4 In allopatric speciation, geographic isolation leads to speciation

In allopatric speciation, populations of the same species are geographically separated, separating their gene pools

Changes in the allele frequencies of each population may be caused by natural selection, genetic drift, and mutation, unaffected by gene flow from other populations


Gene flow between populations is initially prevented by a geographic barrier

– The Grand Canyon and Colorado River separate two species of antelope squirrels


A. leucurusA. harrisi

South North


Likelihood of allopatric speciation increases when a population is small and isolated

– A small population may have a different gene pool due to the founder effect

– Genetic drift and natural selection may have a greater effect in a small population in a new habitat



14.5 In sympatric speciation, speciation takes place without geographic isolation

In sympatric speciation, new species may arise within the same geographic area as a parent species

Gene flow between populations may be reduced by factors such as polyploidy, habitat differentiation, or sexual selection


Many plant species have evolved by polyploidy, the multiplication of the chromosome number due to errors in cell division

A tetraploid (4n) plant can arise from a diploid parent


Parent species2n = 6

Tetraploidcells

4n = 12

1


Tetraploidcells

4n = 12

1

Diploidgametes

2n = 6

2


Tetraploidcells

4n = 12

1

Diploidgametes

2n = 6

2

Viable, fertiletetraploidspecies4n = 12

Self-fertilization

3


Most polyploids arise from hybridization of two different species

Haploid gametes from two different species combine to produce a sterile hybrid

– Why is the hybrid sterile? How can it reproduce?

Chromosome duplications may produce a fertile polyploid species

– What is the chromosome number of the new species


Species A2n = 4

Gameten = 2

Species B2n = 6

Gameten = 3

Species A2n = 4

Gameten = 2

1 2

Species B2n = 6

Gameten = 3

Sterile hybridn = 5

Chromosomes nothomologous(cannot pair)

Species A2n = 4

Gameten = 2

1 2

Species B2n = 6

Gameten = 3

Sterile hybridn = 5

Chromosomes nothomologous(cannot pair)

Viable, fertilehybrid species

2n = 10

3


Sympatric speciation in animals more commonly occurs through habitat differentiation and sexual selection

– Remember the cichlids in Lake Victoria!



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

80% of all living plant species are the descendants of ancestors that formed by polyploid speciation

Hybridization between two species accounts for most of these species

– What advantage might there be to hybridization?

Polyploid food plants include oats, potatoes, bananas, peanuts, barley, plums, apples, sugarcane, coffee, and bread wheat

Cotton is also polyploid


Wheat has been domesticated for 11,000 years

– It is the most widely cultivated plant in the world

Bread wheat, Triticum aestivum, is a polyploid with 42 chromosomes

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

Triticum monococcum

(14 chromosomes)Hybridization

AA BB

AB

Sterile hybrid

(14 chromosomes)

1

2

´

Cell division error

and self-fertilization

Wild

Triticum

(14 chromo-

somes)

AA BB DD´

Sterile hybrid

(21 chromosomes)

ABD

Hybridization3

4 Cell division error


T. tauschii

(wild)

(14 chromosomes)

T. turgidum

Emmer wheat

(28 chromosomes)

AA BB DD

T. aestivum

Bread wheat

(42 chromosomes)

Triticum monococcum(14 chromosomes)

Hybridization

AA BB

AB

Sterile hybrid

(14 chromosomes)

1

´

Cell division errorand self-fertilization

WildTriticum(14 chromo-somes)

AA BB

T. turgidumEmmer wheat(28 chromosomes)

2

AA BB DD´

Sterile hybrid(21 chromosomes)

ABD

Hybridization3

4 Cell division error


T. tauschii(wild)(14 chromosomes)

T. turgidumEmmer wheat(28 chromosomes)

AA BB DD

T. aestivumBread wheat(42 chromosomes)


14.7 Reproductive barriers may evolve as populations diverge

How do reproductive barriers arise?

Initial sampleof fruit flies Maltose mediumStarch medium

Mating frequenciesin experimental groups

Starch

Mating frequenciesin starch control groups

Maltose

Mating experiments

ResultsFemale

Female

Sta

rch

Ma

lto

se

22 9

8 20Ma

le

Population Population

Po

p#1

Po

p#2

18 15

12 15M

ale

#1 #2


14.8 Hybrid zones provide opportunities to study reproductive isolation

What happens when isolated populations renew contact?

In hybrid zones, members of different species meet and mate to produce hybrid offspring

Ancestralspecies

21

Gene flow

Population(five individualsare shown)

Barrier togene flow

Newspecies

Hybridzone

Hybrid

Gene flow

3

4

Reinforcement StabilityFusion

Malecollaredflycatcher

Malepiedflycatcher

Allopatricpopulations

Sympatricpopulations

Pied flycatcher fromallopatric population

Pied flycatcher fromsympatric population

Malecollaredflycatcher

Malepiedflycatcher

Allopatricpopulations

Sympatricpopulations

Pied flycatcher fromallopatric population

Pied flycatcher fromsympatric population


What may happen in a hybrid zone?

Reinforcement: If hybrids are less fit than parent species, natural selection strengthens reproductive barriers

Fusion: Weak reproductive barriers between the two species, with considerable gene flow, reverses speciation and two species become one again



Stability: Many hybrid zones are stable, continuing to produce hybrids; this allows some gene flow between populations, but each species maintains its own integrity

– Which of these three outcomes—reinforcement, fusion, or stability—is happening to the Pundamilia species of cichlids in Lake Victoria?



Peter and Rosemary Grant have worked on medium ground finches on tiny, isolated, uninhabited Daphne Major in the Galapágos Islands for 35 years

Medium ground finches and cactus finches occasionally interbreed

– Hybrid offspring have intermediate bill sizes and survive well during wet years, when there are plenty of soft, small seeds around

– During dry years, hybrids are outcompeted by both parental types

14.9 TALKING ABOUT SCIENCE: Peter and Rosemary Grant study the evolution of Darwin’s finches


The occasional hybridization between finch species introduces new genes into both populations

During drought years, hybrids die out

– This keeps medium ground finches and cactus finches on separate evolutionary paths

14.9 TALKING ABOUT SCIENCE: Peter and

Rosemary Grant study the evolution of

Darwin’s finches

Cactus-seed-eater(cactus finch)

Seed-eater(medium ground finch)

Tool-using insect-eater(woodpecker finch)

Cactus-seed-eater(cactus finch)

Seed-eater(medium ground finch)

Tool-using insect-eater(woodpecker finch)


14.10 Adaptive radiation may occur when new opportunities arise

In adaptive radiation, many diverse species evolve from a common ancestor

Adaptive radiations occur

– When a few organisms colonize new unexploited areas

– After a mass extinction

Adaptive radiations are linked to new opportunities: lack of competitors, varying habitats and food sources, evolution of new structures


14.11 Speciation may 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 and rarely took less than 50,000 years

Animation: Macroevolution

14_11Macroevolution_A.html

Prezygotic barriers

• Temporal isolation

• Habitat isolation

• Behavioral isolation

• Mechanical isolation

• Gametic isolation

Zygote

Gametes Postzygotic barriers

•

•

•

Viable,fertile

offspringReduced hybrid

viability

Reduced hybrid

fertility

Hybrid breakdown

Species

may interbreedin

outcome may be

a.

a fewhybrids

continue tobe produced

f.e.

b. c. d.

speciesseparate

speciationreversed

reproductivebarriers

when

are

keeps

whenwhen

are

and


You should now be able to

1. Explain how the diverse assemblage of cichlid species evolved in Lake Victoria; explain why many of these species no longer exist

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 belonging to closely related species from interbreeding


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

5. Explain how sympatric speciation can occur, noting examples in plants and animals

6. Explain why polyploidy is important to modern agriculture; explain how modern wheat evolved

7. Explain how reproductive barriers might evolve in isolated populations of organisms



8. Explain how hybrid zones are useful in the study of reproductive isolation

9. Explain the conditions that can lead to adaptive radiation


chapter 14 the origin of species - napa valley college 110/14...initial sample starch medium of...

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