24 lectures p p t
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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
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Overview: The “Mystery of Mysteries”
• In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth
Video: Galápagos Tortoise
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• 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
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• 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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LE 24-2LE 24-2
Anagenesis Cladogenesis
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Concept 24.1: The biological species concept emphasizes reproductive isolation
• Species is a Latin word meaning “kind” or “appearance”
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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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LE 24-3LE 24-3
Similarity between different species.
Diversity within a species.
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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
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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
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• 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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LE 24-4aLE 24-4a
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
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• Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes
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• Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers
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• Mechanical isolation: Morphological differences can prevent successful mating
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• 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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LE 24-4aaLE 24-4aa
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
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• Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult:
– Reduced hybrid viability
– Reduced hybrid fertility
– Hybrid breakdown
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• Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development
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• Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile
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• 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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LE 24-4abLE 24-4ab
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
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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
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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
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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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LE 24-5LE 24-5
Allopatric speciation Sympatric speciation
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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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LE 24-6LE 24-6
A. harrisi A. leucurus
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• To determine if allopatric speciation has occurred, reproductive isolation must have been established
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LE 24-7aLE 24-7a
Initial populationof fruit flies(Drosophila
pseudoobscura)
Mating experimentsafter several generations
Some fliesraised on
maltose medium
Some fliesraised on
starch medium
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LE 24-7bLE 24-7b
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
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Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes place in geographically overlapping populations
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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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LE 24-8LE 24-8
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
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• An allopolyploid is a species with multiple sets of chromosomes derived from different species
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LE 24-9LE 24-9
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
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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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LE 24-10LE 24-10
Normal light Monochromatic orange light
P. pundamilia
P. nyererei
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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
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Adaptive Radiation
• Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities
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• The Hawaiian archipelago is one of the world’s great showcases of adaptive radiation
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LE 24-12LE 24-12
KAUAI5.1
millionyears OAHU
3.7millionyears
HAWAII0.4
millionyears
1.3millionyears
MAUIMOLOKAI
LANAI Argyroxiphium sandwicense
Dubautia linearisDubautia scabra
Dubautia waialealae
Dubautia laxa
N
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Studying the Genetics of Speciation
• The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation
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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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LE 24-13LE 24-13
Time
Gradualism model Punctuated equilibrium model
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Concept 24.3: Macroevolutionary changes can accumulate through many speciation events
• Macroevolutionary change is cumulative change during thousands of small speciation episodes
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Evolutionary Novelties
• Most novel biological structures evolve in many stages from previously existing structures
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• Some complex structures, such as the eye, have had similar functions during all stages of their evolution
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LE 24-14LE 24-14
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
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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
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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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LE 24-15aLE 24-15a
Differential growth rates in a human
NewbornAge (years)
Adult2 5 15
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• Different allometric patterns contribute to the contrasting shapes of human and chimpanzee skulls
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LE 24-15bLE 24-15b
Chimpanzee fetus Chimpanzee adult
Human fetus Human adult
Comparison of chimpanzee and human skull growth
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• Heterochrony has also played a part in the evolution of salamander feet
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LE 24-16LE 24-16
Ground-dwelling salamander
Tree-dwelling salamander
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• 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
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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
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• 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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LE 24-18LE 24-18
Chicken leg bud
Region ofHox gene
expression
Zebrafish fin bud
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• Evolution of vertebrates from invertebrate animals was associated with alterations in Hox genes
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LE 24-19LE 24-19
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
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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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LE 24-20LE 24-20
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
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• 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