how did this flightless bird come to live on the isolated
TRANSCRIPT
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Food for thoughtHow did this flightless bird come to live on the isolated
Galápagos Islands?
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EVOLUTION & SPECIATION
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What species
is this?
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Equus asinus× Equus caballusMules and hinnies have 63 chromosomes,
a mixture of the horse's 64 and the donkey's 62
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How did this flightless bird come to live on the isolated Galápagos Islands?
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© 2011 Pearson Education, Inc.
Animation: Macroevolution Right-click slide / select “Play”
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VOCABULARY REVIEW
• EVOLUTION – CHANGE OVER TIME
• NATURAL SELECTION - INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT ARE ABLE TO SURVIVE & REPRODUCE.
• A.K.A. “SURVIVAL OF THE FITTEST”
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NEW VOCABULARY
• POPULATION – GROUP OF INDIVIDUALS OF SAME SPECIES THAT INTERBREED
• GENE POOL – COMMON GROUP OF ALL GENES PRESENT IN A POPULATION
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Gene Pool
Combined genetic info. of all members
Allele frequency is # of times alleles occur
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Variation in Populations
2 processes can
lead to this:
Mutations -
change in DNA
sequence
Gene Shuffling –
from sexual
reproduction
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Genetic Drift changes populations…….
• Random change in allele frequency causes an allele to become common
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• Founder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population
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• Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)
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• Nonrandom mating: inbreeding and assortive mating (both shift frequencies of different genotypes)
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• Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment
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Sexual selection• Sexual dimorphism:
secondary sex characteristic distinction
• Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism
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Evolution of Populations
Occurs when there is a change in relative frequency of alleles
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Generation 1: 1.00 not resistant0.00 resistant
Resistance to antibacterial soap
How natural selection works
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Resistance to antibacterial soap
Generation 1: 1.00 not resistant0.00 resistant
How natural selection works
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Resistance to antibacterial soap
mutation!
Generation 1: 1.00 not resistant0.00 resistant
Generation 2: 0.96 not resistant0.04 resistant
How natural selection works
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Resistance to antibacterial soap
Generation 1: 1.00 not resistant0.00 resistant
Generation 2: 0.96 not resistant0.04 resistant
Generation 3: 0.76 not resistant0.24 resistant
How natural selection works
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Resistance to antibacterial soap
Generation 1: 1.00 not resistant0.00 resistant
Generation 2: 0.96 not resistant0.04 resistant
Generation 3: 0.76 not resistant0.24 resistant
Generation 4: 0.12 not resistant0.88 resistant
How natural selection works
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Phenotype Expression
• Depends on how many genes control that trait
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Single-Gene vs. Polygenic Traits
Single-Gene:
2 Distinct Phenotypes
Polygenic:
Many Phenotypes
(EG: tongue rolling)
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Allele Frequencies
Natural Selection Genetic Drift
Single Gene
Traits
Polygenic
Traits
Directional
Selection
Stabilizing Selection
Disruptive Selection
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Natural Selection on Polygenic Traits
• Shifts to
middle range
• Shifts to
2 extremes
• Shifts to
1 extreme
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Conditions needed for Genetic Equilibrium
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SPECIATION
• THE FORMATION OF NEW SPECIES
• AS NEW SPECIES EVOVLVE, POPULATIONS BECOME REPRODUCTIVELY ISOLATED
• REPRODUCTIVE ISOLATION – the existence of a barrier that prevents 2 populations from breeding…
• MEMEBERS OF 2 POPULATIONS CANNOT INTERBREED & PRODUCE FERTILE OFFSPRING.
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Scale of evolution:
• Microevolution consists of changes in allele frequency in a population over time
• Macroevolution refers to broad patterns of evolutionary change above the species level
© 2011 Pearson Education, Inc.
Process of species change
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What defines a species?
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The biological species concept emphasizes reproductive isolation
• Biological Species Concept (one way to divide species):
• A species is a group of populations whose members can breed and produce viable, fertile offspring• Ability to mate = formation of a species
• Gene flow between populations holds together the phenotype of a population (ongoing exchange of alleles)
© 2011 Pearson Education, Inc.
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It’s all about ability to breed
(a) Similarity between different species
(b) Diversity within a species
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Reproductive Isolation is the driving force behind Speciation
• A new species will form when reproductive isolationoccurs
• Absence of gene flow
• Reproductive Isolation:• The existence of biological factors (barriers) that prevent two
individuals of a species from mating and producing viable and fertile offspring
© 2011 Pearson Education, Inc.
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Figure 24.3_b
Prezygotic barriers
Habitat
Isolation
Temporal
Isolation
Behavioral
Isolation
Mechanical
Isolation
Gametic
Isolation
Individuals of
differentspecies
MATINGATTEMPT
FERTILIZATION
(a) (c) (e) (f)
(b)
(g)
(d)
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Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
FERTILIZATION
VIABLE,FERTILE
OFFSPRING
Postzygotic barriers
(k)
(h) (i)
(j)
(l)
Figure 24.3_c
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Limitations of the Biological Species Concept
• The biological species concept (BSC) cannot be applied to fossils or asexual organisms (including all prokaryotes)
• The biological species concept emphasizes absence of gene flow
However, gene flow can occur between distinct species
• HYBRIDS: For example, grizzly bears and polar bears can mate to produce “grolar bears”
© 2011 Pearson Education, Inc.
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Figure 24.4Grizzly bear (U. arctos)
Polar bear (U. maritimus)
Hybrid “grolar bear”
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Other Definitions of Species2. morphological species concept:
• A species is characterized by its body shape
• It applies to sexual and asexual species but relies on subjective criteria
3. ecological species concept:• A species is characterized by its ecological niche
• It applies to sexual and asexual species and emphasizes the role of disruptive selection
4. phylogenetic species concept:• A species is the smallest group of individuals that share a
common ancestor
• It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species
© 2011 Pearson Education, Inc.
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Bellwork:
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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
• What do the route words mean?
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Figure 24.5
(a) (b)Allopatric speciation.
A population forms a
new species while
geographically isolated
from its parent population.
Sympatric speciation.
A subset of a population
forms a new species
without geographic
separation.
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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
• For example, the flightless cormorant of the Galápagos likely originated from a flying species on the mainland
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The Process of Allopatric Speciation
• The definition of barrier depends on the ability of a population to disperse
• For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen
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A. harrisii A. leucurus
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ALLOPATRIC SPECIATION
A. formosus
Atlantic Ocean
A. nuttingi
Isthmus of Panama
Pacific Ocean
A. panamensis A. millsae
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Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes place in geographically overlapping populations
• In a sympatric speciation, various factors can limit gene flow:
• Polyploidy• Habitat differentiation• Sexual selection
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Reproductive Isolation Mechanism• BEHAVIORAL ISOLATION- CAPABLE OF
BREEDING BUT HAVE DIFFERENCES IN COURTSHIP RITUALS (EX. MEADOWLARKS)
• GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE RIVERS, MOUNTAINS, OR BODIES OF WATER (EX. SQUIRREL)
• TEMPORAL ISOLATION – 2 OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES.
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Table 23.1a
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Tigon
Result of male tiger and female lion mating incaptivity. Offspring are infertile.
Separated both geographically and ecologically.
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Liger
Result of male lion and female tiger mating in captivity. Offspring are infertile.
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Table 23.1b
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Fig. 23.6
Four species of leopard frogs: differ in their mating calls. Hybrids are inviable.
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These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation.
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Hawaiian Honeycreepers
FOUNDER SPECIES
An example of adaptive radiation –these species all diverged from acommon ancestor (founder species)
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SPECIATION IN DARWIN’SFINCHES
• SPECIAITON IN THE GALAPAGOS FINCHES OCCURRED BY:
- FOUNDING OF A NEW POPULATION,
- GEOGRAPHIC ISOLATION which led to -- REPRODUCTIVE ISOLATION and
CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.
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