SPECIATION

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SPECIATION

• Review for Lecture 221

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Info for advising

• Science majors should sign up for
• Biol 201 (Invertebrate zoology with Dr. Martin)
• Chem 112 (only if youre taking chem 111 now)
• Math 121 or 206 and/or foreign language
• CORE maybe honors
• English 120 (freshmen), maybe PE
• maybe exploring other departments or biology
  seminar (BIOL 460)
• See 103 web site for links to more info

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most important concept

•      
• DNA -gtmore DNA --gt RNA -gt adaptation
• This "central dogma" of today's molecular biology
  has applications
• in natural selection and speciation.

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Reviewing Chapter 20 21

• Natural Selection survival and reproduction of
  the fittest.
• Individuals have variations
• Variations are genetic
• only some offspring survive and reproduce
• Biologists measure evolution with changes in gene
  frequencies

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Mechanisms of Evolutionary Change

• Mechanisms that change allele frequencies in
  populations
• Natural selection
• Mutation
• Gene flow
• Genetic drift
• Natural selection is the only mechanism that
  results in adaptation and leads to increased
  fitness.

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Hardy-Weinberg equilibrium no evolution

• conditions
• no mutation
• no migration ( no gene flow)
• large population with no genetic drift
• random mating
• no selection no genetic advantage in survival
  or reproduction

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Hardy-Weinberg equilibrium no evolution

• The factors which can change the Hardy-Weinberg
  equilibrium give biologists
• a method of measuring the rate of evolution and
• they guide biologists to focus on the possible
  sources of changes in frequency distribution
  (like increased mortality in bigger babies)

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Mechanisms of Evolutionary Change

• Mechanisms that change allele frequencies in
  populations
• Natural selection
• Mutation
• Gene flow
• Genetic drift
• Natural selection is the only mechanism that
  results in adaptation and leads to increased
  fitness.

9
RANDOM mating?

• In nature, matings between individuals are
  seldom, if ever, random.
• In small populations, matings between relatives
  are common. This is known as inbreeding.

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Table 22.3
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The Importance of Genetic Diversity

• Evolution cannot occur without genetic diversity
  since there would be no variation for natural
  selection to act on.

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Figure 22.5
SURVEYING ALLELIC DIVERSITY IN POPULATIONS
1. Take blood samples from many individuals and
isolate proteins.
2. Load protein samples from different
individuals into wells in gel.
3. Put gel into an electric field. Proteins
separate according to charge and mass.
4. Treat gel with a solution that stains a
specific enzyme. One band implies that the
individual is homozygous at the locus for the
enzyme. Two bands imply that the individual is
heterozygous at this locus.
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RANDOM mating?

• In nature, matings between individuals are
  seldom, if ever, random.
• In small populations, matings between relatives
  are common. This is known as inbreeding.

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Sexual Selection

• a continuing controversy.
• Darwin invented this term to explain cases in
  which bright colors and fancy equipment, like a
  peacock's tail, seem to evolve simply to attract
  mates despite their probable disadvantages in
  survival.

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Figure 22.10 a,b,c
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Figure 22.11a
Males compete for the opportunity to mate with
females.
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Figure 22.11b
Variation in reproductive success is greater for
males than females.
100
Males
75
Percentage males born
50
25
0
81-100
41-50
11-20
1-10
0
75
Females
50
Percentage females born
25
0
0
1
2
3
4
5
6
7
8
9
10
Number of offspring weaned
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Darwin's four postulates

• Individuals have variations
• Variations are genetic
• only some offspring survive and reproduce
• Natural Selection survival and reproduction of
  the fittest.

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Mechanisms of Evolutionary Change

• Evolution is defined as a change in allele
  frequencies over time.
• Natural selection acts on individuals, but
  evolutionary change occurs in populations.

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EVIDENCE WE CAN OBSERVE

• Extinctions
• fossils
• structural homologies
• developmental homologies
• genetic homologies
• vestigial traits
• changes in adaptations
• repeated patterns in all of the above

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Analyzing Allele Frequency Change The
Hardy-Weinberg Model

• If no evolution is occurring, then allele
  frequencies will be the same in a parental and
  offspring generation.

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Figure 22.3
DERIVING THE HARDY-WEINBERG PRINCIPLE-A NUMERICAL
EXAMPLE
P1 frequency of allele A1 0.7
1. Suppose that the allele frequencies in the
parental generation were 0.7 and 0.3.
P2 frequency of allele A2 0.3
Gametesfrom parent generation
2. 70 of the gametes in the gene pool carry
allele A1 and 30 carry allele A2 .
3. Pick two gametes at random from the gene pool
to form offspring. Three genotypes are possible.
A2
A1
A1
A2
A1
A1
A2
A2
.07 x 0.30.21
.03 x 0.70.21
0.7 x 0.7 0.49
0.3 x 0.3 0.09
0.21 0.21 0.42
Homozygous
Heterozygous
Homozygous
4. Calculate the frequencies of these three
combinations of alleles.
Gametesfrom offspring generation
5. When the offspring breed, imagine that their
gametes go into a gene pool.
6. Calculate the frequencies of the two alleles
in this gene pool.
42 of the gametes are from A1A2 parents. Half of
these carry A1and half carry A2
49 of the gametes are from A1A1 parents. All of
these carry A1
9 of the gametes are from A2A2 parents. All of
these carry A2
BEHOLD! The allele frequencies of A1and A2 have
not changed from parent generation to offspring
generation. Evolution has not occurred.
P1 frequency of allele A1 (0.49 1/2(0.42))
(0.49 0.21) 0.7
P2 frequency of allele A2 (1/2(0.42) 0.09)
(0.21 0.09) 0.3
Genotype frequencies will be given by p12
2p1p2 p22 as long as all Hardy-Weinberg
assumptions are met
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Figure 22.4
1. Start long-term experiment by placing 10 mL of
identical growth medium and a genetically
identical E. coli cell to many replicate tubes.
2. Incubate overnight. Average population in each
tube is now 5 x 108 cells.
3. Remove 0.1 mL from each tube and move to 10
mL of fresh medium. Freeze remaining cells for
later analysis.
4. Take cells from generation 1 and add a genetic
marker so that they can be identified.
5. Put an equal number of cells from generation 1
and a later generation in fresh growth medium.
6. Incubate overnight and count the cells. Which
are more numerous?
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most important concept

•      
• Darwins theory NATURAL SELECTION

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most important concept for Chapter 23

•     
• Scientists' theories about species and speciation
  are evolving, but natural selection in isolated
  gene pools is still the main focus.

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What is a species?

• Ideal types Before Darwin, scientists thought
  of species as recognizable descendents of an
  "ideal type" created by God, and even today
  scientists often use "species" to mean a visibly
  distinctive group of plants or animals
  (morphospecies).

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Ideal types Not

• One of Darwins greatest contributions
• Variation is natural, not degenerate

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What is a species?

• Ideal types and morphospecies?
• Morphospecies differs from ideal type in that
  genetic variation is expected.
• After Darwin, scientists realized that many
  species have so much genetic diversity it becomes
  impossible to define the "ideal" or even
  "typical" member.

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What is a species?

• From the only
• illustration in
• Darwins
• Origin of
• Species

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What is a species?

• As scientists learned more about genetics, they
  began to define a species as all the members of a
  gene pool.
• (Biological species concept)

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What is a species?

• And as scientists learned more about evolutionary
  details, they began to define a species as all
  the members of a gene pool (Biological species
  concept) with monophyletic ancestry
• (phylogenetic species)

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Figure 23.2
B
C
D
E
F
G
H
J
I
A
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phylogenetic species?

• the trendy concept among taxonomists today
• Tree of Life web page
• Phylotree web page
• http//www.ucmp.berkeley.edu/alllife/
• but there are problems.

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Figure 23.10
Hybrids inherit species-specific mtDNA sequences
from their mothers.
Hybrids have intermediate characteristics.
Townsends warbler
All individuals have Townsends mtDNA
Some individuals have Townsends mtDNA, others
have hermit mtDNA
Townsends-hermit hybrid
Pacific Ocean
Hermit warbler
All individuals have hermit mtDNA
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Can a hybrid be a phylogenetic species?

• K?

B
C
D
E
G
H
J
I
A
F
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What is a species?

• its a fluid concept
• should we think of gene pools separating and
  merging like bubbles so that you have a
  phylo-web?

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Table 23.1
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Speciation requires isolation

• isolation of gene pools (always)
• change in genes (always)genetic change is caused
  by
• genetic drift in small gene pools usually
• natural selection usually
• mutations (including ploidies) usually

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Figure 23.8 left
DISPERSAL AND COLONIZATION
1. Start withone continuouspopulation.Then, a
colonistfloats to anisland on a raft.
Island
Continent
2. Finish withtwo populationsisolated fromone
another.
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Figure 23.8 right
VICARIANCE
1. Start withone continuouspopulation.Then a
chanceevent occursthat changesthe landscape
(river changes course).
River
2. Finish withtwo populationsisolated fromone
another.
River changes course
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Isolation in Allopatry is Spatial

• Allopatric speciation begins when sub-populations
  become physically separated from each other.
• Then divergent genetic changes accumulate.

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Isolation in Sympatry is Biological

• Sympatric speciation begins in populations that
  occupy the same geographic area but become
  reproductively isolated by a biological factor,
  like food or a genetic change which affects
  reproduction.
• Then, with two gene pools, more changes evolve.

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Chapter 23
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Figure 23.5a
Beak length correlates with fruit size.
Balloon vine (native species)
Flat-poddedgolden rain tree(non-native species)

Short-beaked populationgrowing on
non-nativeplants
12
Long-beaked populationgrowing on native plants
8
4
0
Frequency
2
3
6
7
8
9
10
11
12
Beak length (mm)
8
Non-native plant(small fruit)
Native plant(large fruit)
4
0
2
3
6
7
8
9
10
11
12
Fruit radius (mm)
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Figure 23.6
Diploid parent
Tetraploid parent
(Four copies of each chromosome)
(Two copies of each chromosome)
Meiosis
Mating
Diploid gametes
Haploid gametes
(One copy of each chromosome)
(Two copies of each chromosome)
Triploid zygote
Meiosis
(Three copies of each chromosome)
When these gametes combine, most offspring have
incorrect number of chromosomes.
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Sympatric speciation is still a little
controversial

• Its often instant like polyploidy or even
  smaller chromosomal mutations or even point
  mutations affecting reproduction.
• Its harder to understand unless you can imagine
  many examples of reproductive isolation.

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Applying Darwin's ideas

• Did some skypilots inherit adaptations which
  helped them survive and reproduce better than
  others in a specific habitat?

48
Figure 21.7 a,b
In tundra habitats above timberline, the alpine
skypilot is pollinated primarily by bumblebees.
28 24 20 16 12 8 4 0
Number of individuals
10 12 14 16 18 20 22
Tundra flower big and sweet-smelling
Flower size (mm)
In forested habitats below timberline, the alpine
skypilot is pollinated primarily by flies.
10
8
6
Number of individuals
4
2
0
10 12 14 16 18 20 22
Below-timberline flower small and
skunky-smelling
Flower size (mm)
49
Applying Darwin's ideas

• Are skypilots diverging into separate species?
• Would this be an example of allopatry or sympatry?

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Applying Darwin's ideas

• Are human races diverging into separate species?
  
• The book describes some interpretations of human
  races. What is Freeman's point?
• In your own opinion, why does it matter?
• Should we encourage research about genetic
  differences among different ethnic groups

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most important concept

•     
• Scientists' theories about species and speciation
  are evolving, but natural selection in isolated
  gene pools is still the main focus.
• Species and speciation are fluid concepts.

52
Preview of Mondays Assignment

•      

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History of Life on Earth
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Mechanisms of Evolutionary Change

• Evolution is defined as a change in allele
  frequencies over time.
• Natural selection acts on individuals, but
  evolutionary change occurs in populations.

55
EVIDENCE WE CAN OBSERVE

• Extinctions
• fossils
• structural homologies
• developmental homologies
• genetic homologies
• vestigial traits
• changes in adaptations
• repeated patterns in all of the above

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Major topics in the History of Life Chapter

•      
• Fossils, including isotope-based dating
• Phylogenies based on genetic homologies

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Figure 23.2
B
C
D
E
F
G
H
J
I
A
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Box 23.1, Figure 1
Cow
Deer
Whale
Hippo
Pig
Peccary
Camel
8, 11, 14, 15
4, 5, 6, 7
19, 20
10, 12
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I have recently read that chimp DNA is 95 the
same as that of humans and the recently decoded
mouse genome is about 97 the same as humans. If
this is the case, what could it mean genetics
wise in our relationship?

• The two studies were using different analyses of
  DNA so it's hard to know which figures are
  right. Other studies have said chimp DNA is more
  than 99 the same as human DNA. So you have to
  figure what they mean by the percentages
• are they based on total base sequences (very
  likely not)?
• homologous genes? Or SNPs in selected genes?
  
• functional mutations only or also silent
  mutations?
• only coding DNA or analyses including introns,
  SINES, LINES, etc.?
• A lot of this sort of information comes from
  indirect evidence like estimates based on
  centrifuge-calculated weights of hybridized
  DNA/RNA (like in probes).
• So you can't compare two studies unless you know
  what both studies used to calculate their
  percentages.

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Figure 22.9b
For example, only juvenile blackbellied
seedcrackers with very longor very short beaks
survived long enough to breed.
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20
Number of individuals
10
0
11
6
7
10
8
9
Beak length (mm)
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Figure 23.1
Large ground finch
Small ground finch
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Darwin's concept

• Natural Selection survival and reproduction of
  the fittest.

63
Darwin's four postulates

• Individuals have variations
• Variations are genetic
• only some offspring survive and reproduce
• Natural Selection survival and reproduction of
  the fittest.

64
MORE ABOUT

• Darwin http//www.queens.edu/faculty/jannr/darwin.
  htm
• Creationism
• http//www.queens.edu/faculty/jannr/creationism.ht
  m
• Evolution
• http//www.queens.edu/faculty/jannr/evolution.htm