24 Lectures P P T

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 24Chapter 24

The Origin of Species


Overview: The “Mystery of Mysteries”

• In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth

Video: Galápagos Tortoise



• Speciation, the origin of new species, is at the focal point of evolutionary theory

• Evolutionary theory must explain how new species originate and how populations evolve

• Microevolution consists of adaptations that evolve within a population, confined to one gene pool

• Macroevolution refers to evolutionary change above the species level


• Two basic patterns of evolutionary change:

– Anagenesis (phyletic evolution) transforms one species into another

– Cladogenesis (branching evolution) is the splitting of a gene pool, giving rise to one or more new species

Animation: Macroevolution

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Anagenesis Cladogenesis


Concept 24.1: The biological species concept emphasizes reproductive isolation

• Species is a Latin word meaning “kind” or “appearance”


The Biological Species Concept

• Members of a biological species are reproductively compatible, at least potentially; they cannot interbreed with other populations.

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Similarity between different species.

Diversity within a species.


Reproductive Isolation

• Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile hybrids

• Two types of barriers: prezygotic and postzygotic


• Prezygotic barriers impede mating or hinder fertilization if mating does occur:

– Habitat isolation

– Temporal isolation

– Behavioral isolation

– Mechanical isolation

– Gametic isolation


• Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers

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Prezygotic barriers impede mating or hinder fertilization if mating does occur

Postzygotic barriers prevent a hybrid zygote fromdeveloping into a viable, fertile adult

REDUCED HYBRIDVIABILITY

REDUCED HYBRIDFERTILITY

HYBRID BREAKDOWN

HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION GAMETIC ISOLATION

Reducedhybrid

viability

FertilizationViable,fertile

offspring

Reducedhybridfertility

Hybridbreakdown

Matingattempt

Gameticisolation

Fertilization

Mechanicalisolation

Behavioralisolation

Temporalisolation

Habitatisolation

Individualsof

differentspecies


• Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes




• Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers



• Mechanical isolation: Morphological differences can prevent successful mating



• Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species

Video: Blue-footed Boobies Courtship Ritual

Video: Giraffe Courtship Ritual

Video: Albatross Courtship Ritual


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Prezygotic barriers impede mating or hinder fertilization if mating does occur

HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION GAMETIC ISOLATION

Matingattempt

Gameticisolation

Fertilization

Mechanicalisolation

Behavioralisolation

Temporalisolation

Habitatisolation

Individualsof

differentspecies


• Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult:

– Reduced hybrid viability

– Reduced hybrid fertility

– Hybrid breakdown


• Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development



• Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile



• Hybrid breakdown: Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile


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Postzygotic barriers prevent a hybrid zygote fromdeveloping into a viable, fertile adult

REDUCED HYBRIDVIABILITY

REDUCED HYBRIDFERTILITY

HYBRID BREAKDOWN

Reducedhybrid

viability

FertilizationViable,fertile

offspring

Reducedhybridfertility

Hybridbreakdown


Limitations of the Biological Species Concept

• The biological species concept does not apply to

– Asexual organisms

– Fossils

– Organisms about which little is known regarding their reproduction


Other Definitions of Species

• Morphological: defines a species by structural features

• Paleontological: focuses on morphologically discrete species known only from the fossil record

• Ecological: views a species in terms of its ecological niche

• Phylogenetic: defines a species as a set of organisms with a unique genetic history


Concept 24.2: Speciation can take place with or without geographic separation

• Speciation can occur in two ways:

– Allopatric speciation

– Sympatric speciation

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Allopatric speciation Sympatric speciation


Allopatric (“Other Country”) Speciation

• In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations

• One or both populations may undergo evolutionary change during the period of separation

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A. harrisi A. leucurus


• To determine if allopatric speciation has occurred, reproductive isolation must have been established

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Initial populationof fruit flies(Drosophila

pseudoobscura)

Mating experimentsafter several generations

Some fliesraised on

maltose medium

Some fliesraised on

starch medium

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FemaleFemale

Starch Maltose

Sta

rch

Mal

toseM

ale

Samepopulation

Differentpopulations

Mal

e

208

Mating frequenciesin experimental group

Mating frequenciesin control group

18 15

1512

Sam

ep

op

ula

tio

nD

iffe

ren

tp

op

ula

tio

ns

922


Sympatric (“Same Country”) Speciation

• In sympatric speciation, speciation takes place in geographically overlapping populations


Polyploidy

• Polyploidy is presence of extra sets of chromosomes due to accidents during cell division

• It has caused the evolution of some plant species

• An autopolyploid is an individual with more than two chromosome sets, derived from one species

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Failure of cell division in a cell of a growing diploid plant after chromosome duplication gives rise to a tetraploid branch or other tissue.

Gametes produced by flowers on this tetraploid branch are diploid.

Offspring with tetraploid karyo-types may be viable and fertile—a new biological species.

2n = 64n = 12 4n

2n


• An allopolyploid is a species with multiple sets of chromosomes derived from different species

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Species B2n = 6

Species A2n = 4

Normal gameten = 3

Normal gameten = 3

2n = 10

Unreduced gametewith 4 chromosomes

Unreduced gametewith 7 chromosomes

Hybrid with7 chromosomes

Viable fertile hybrid(allopolyploid)

Meiotic error;chromosomenumber notreduced from2n to n


Habitat Differentiation and Sexual Selection

• Sympatric speciation can also result from the appearance of new ecological niches

• In cichlid fish, sympatric speciation has resulted from nonrandom mating due to sexual selection

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Normal light Monochromatic orange light

P. pundamilia

P. nyererei


Allopatric and Sympatric Speciation: A Summary

• In allopatric speciation, a new species forms while geographically isolated from its parent population

• In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species


Adaptive Radiation

• Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities



• The Hawaiian archipelago is one of the world’s great showcases of adaptive radiation

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KAUAI5.1

millionyears OAHU

3.7millionyears

HAWAII0.4

millionyears

1.3millionyears

MAUIMOLOKAI

LANAI Argyroxiphium sandwicense

Dubautia linearisDubautia scabra

Dubautia waialealae

Dubautia laxa

N


Studying the Genetics of Speciation

• The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation


The Tempo of Speciation

• The fossil record includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then apparently disappear

• Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change

• The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence

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Time

Gradualism model Punctuated equilibrium model


Concept 24.3: Macroevolutionary changes can accumulate through many speciation events

• Macroevolutionary change is cumulative change during thousands of small speciation episodes


Evolutionary Novelties

• Most novel biological structures evolve in many stages from previously existing structures


• Some complex structures, such as the eye, have had similar functions during all stages of their evolution

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Complex camera-type eye

Pinhole camera-type eye Eye with primitive lens

Patch of pigmented cells Eyecup

Pigmented cells(photoreceptors)

Epithelium

Nerve fibers

Fluid-filled cavity

Epithelium

Pigmentedlayer (retina)

Opticnerve

Pigmentedcells

Nerve fibers

CorneaCellularfluid(lens)

Optic nerve

Cornea

Lens

Optic nerve

Retina


Evolution of the Genes That Control Development

• Genes that program development control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult


Changes in Rate and Timing

• Heterochrony is an evolutionary change in the rate or timing of developmental events

• It can have a significant impact on body shape

• Allometric growth is the proportioning that helps give a body its specific form

Animation: Allometric Growth

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Differential growth rates in a human

NewbornAge (years)

Adult2 5 15


• Different allometric patterns contribute to the contrasting shapes of human and chimpanzee skulls

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Chimpanzee fetus Chimpanzee adult

Human fetus Human adult

Comparison of chimpanzee and human skull growth


• Heterochrony has also played a part in the evolution of salamander feet

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Ground-dwelling salamander

Tree-dwelling salamander


• In paedomorphosis, the rate of reproductive development accelerates compared with somatic development

• The sexually mature species may retain body features that were juvenile structures in an ancestral species



Changes in Spatial Pattern

• Substantial evolutionary change can also result from alterations in genes that control the placement and organization of body parts

• Homeotic genes determine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged


• The products of one class of homeotic genes called Hox genes

• Hox genes provide positional information in the development of fins in fish and limbs in tetrapods

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Chicken leg bud

Region ofHox gene

expression

Zebrafish fin bud


• Evolution of vertebrates from invertebrate animals was associated with alterations in Hox genes

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Hypothetical vertebrateancestor (invertebrate)with a single Hox cluster

First Hox duplication

Hypothetical earlyvertebrates (jawless)with two Hox clusters

Second Hox duplication

Vertebrates (with jaws)with four Hox clusters


Evolution Is Not Goal Oriented

• The fossil record often shows apparent trends in evolution that may arise because of adaptation to a changing environment

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Pleistocene

Sinohippus

Recent

Pliocene

AnchitheriumMiocene

Paleotherium

Oligocene

Propalaeotherium

Eocene Pachynolophus

Hyracotherium

Mesohippus

Miohippus

Orohippus

Epihippus

Key

Grazers

Browsers

Hypohippus

Parahippus

Archaeohippus

Merychippus

CallippusMegahippus

Pliohippus

Nannippus

Hipparion Neohipparion

Hippidion and other generaEquus


• According to the species selection model, trends may result when species with certain characteristics endure longer and speciate more often than those with other characteristics

• The appearance of an evolutionary trend does not imply that there is some intrinsic drive toward a particular phenotype