Report
Natural selection - Coursework Materials
-
University:
Amherst College -
Course:
BIOL 321 | Evolutionary Biology with Lab Academic year:
2006
-
Views:
221
Pages:
41
Author:
lilipaloulihx4
Natural selection...
a difference, on average, in the survival or fecundity of
individuals with certain phenotypes compared to
individuals with alternative phenotypes
Geospiza fortis
Four tenets of natural selection…
(1)! Individuals within populations are variable
(2)! Variation is heritable
(3)! Organisms differ in their ability to survive and reproduce
(4)! Survival & reproduction are non-random Divergent Induced Responses to an
Invasive Predator in Marine
Mussel Populations SCIENCE
AUGUST 2006
Mytilus edulis, Blue mussel!
1988
1817!
Respond to presence of predators by thickening shells
– defense response is inducible –!
Nation! ( 2002 ) laboratory
P = 0.001
IIn
Hemigrapsus sanguineus
Asian shore crab!
Carcinus maenas
European green crab!
I*
i
P = 0.573
Caro s
'*
P = 0.011
r*i
P = 0.145! Rapid Temporal Reversal in
Predator-Driven Natural Selection
Anolis sagrei
Anolis sagrei typically terrestrial
(longer legs ~ faster escape from predators)
Invasion by Leiocephalus carinatus causes
Anolis sagrei to be arboreal
…predicted that leg length would
DECREASE in arboreal populations
of Anolis sagrei lizards following
invasion by Leiocephalus carinatus!
Leiocephalus carinatus Rapid Temporal Reversal in
Predator-Driven Natural Selection
Anolis sagrei
CONTROL!
All Anolis sagrei individuals tagged / measured
Leiocephalus carinatus were introduced on 6 islands
INTRODUCED!
Censused after 6 (and 12) months to record survival
Six INTRODUCTION islands !
Six CONTROL islands !
Longer legs!
CONTROL!
Shorter legs!
May Nov 03
Nov 03 May 04 Components of natural selection
Gamete recognition systems
w ZYGOTES
1I . Viability selection
5. Compatibility
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ADULTS
Females Males
GAMETES
Segregation distortion
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M
4. Gametic
selection
3. Fecundity
selection
Average number viable offspring
Probability of survival before and
during the reproductive period
2’ Sexual selection
PARENTS
Mating success Natural selection is an average difference in the survival or
fecundity of individuals with certain phenotypes
Demonstrating adaptation
What is a trait for? Do individuals that possess the
trait contribute more offspring to future generations?
How does a trait develop? Who has it?
Adaptation
Any heritable trait (structure, physiological ability, behavior)
that makes an organism better able to survive & reproduce
The evolutionary process leading to the persistence of
such a trait in populations Natural selection is the differential contribution of offspring
to the next generation by certain genotypes
Demonstrating adaptation
What is a trait for? Do individuals that possess the
trait contribute more offspring to future generations?
How does a trait develop? Who has it?
Adaptation
Any heritable trait (structure, physiological ability, behavior)
that makes an organism better able to survive & reproduce
The evolutionary process leading to the persistence of
such a trait in populations NATURAL SELECTION ALONG AN
ENVIRONMENTAL GRADIENT: A CLASSIC
CLINE IN MOUSE PIGMENTATION
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The genetic basis of adaptive melanism in
pocket mice
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(Upper) Collecting localities, substrate color, and mouse
color. Sample sizes at each site are given.
Pie charts are the proportion of light and dark mice at
each site. Rectangles indicate substrate color.
(Lower) Light and dark C. intermedius from the Pinacate
locality on light and dark rocks.
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The genetic basis of adaptive melanism in
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Mouse phenotype
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Genotype
DD
in mammals
Association studies using markers in candidate
pigmentation genes (Agouti & Mc1r)
Genotype-phenotype association between Mcr1
alleles & coat color in animals from Pinacate.
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Light
Dark
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0 The Genetic Basis of Phenotypic Convergence in Beach Mice: Similar Pigment
Patterns but Different Genes
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Sceloporus undulatus
Aspidoscelis inornata
Biochemical studies indicate a
different molecular mechanisms
for the derived mutations
Intracellular
Derived amino acid replacements
(1 in each species) are
statistically associated with
blanched coloration
• Integration of receptor into membrane
• Receptor signaling
Hiv”*Tyr substitution for Scctoporus undubtus
Thr 17°ll« siibstitution for Asp ctosce/is inomara
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Lo*Q A pre-adaptation is an existing feature that serves a NOVEL function
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Radial sesamoid There are two main groups of bony fish: the Actinopterygians < wh>ch include
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nearly all modern fish) and the Sarcopterygians (from which humans, and all other tetrapods
)
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evolved. Cartilaginous fish are a related group. Modified from Strickberger 1990 . Reprinted
by permission of the publisher.
Figure 13.4
Reptaea brds.
and mammals
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Perch
Bowlin
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HeopteryQiam
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Chondnchlhyes
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Agnatharis
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Osteichthyes
(bony fish)
Swoopterygans
(iobc limed fish)
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:. The fitness of a genotype is the average lifetime contribution
of individuals of that genotype to future generations
(1)! probability of survival to reproductive age
(2)! average number of offspring produced
Probability and average refer to groups of organisms, thus
fitness is usually defined for a set of individuals
(e.g., members of a particular genotype)
Absolute fitness
Lifetime total fitness (= total number of offspring)
Relative fitness
Degree to which individuals with a particular genotype fare
compared to other genotypes in the population GENETIC ESTIMATES OF ANNUAL AND LIFETIME
REPRODUCTIVE SUCCESS IN MALE RED-WINGED
BLACKBIRDS
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FIG . 1 . True annual reproductive success (no . fledglings
sired) relative to apparent annual reproductive success (no .
young fledged from territory) for male Red- winged Blackbirds for all six years .
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APPARENT SUCCESS
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APPARENT SUCCESS
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FIG . 5 . True lifetime reproductive success ( no . fledglings
sired ) relative to apparent lifetime reproductive success ( no .
young fledged from territory ) for males . , *
r = 0.21
n = 30
P = 0.25
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Absolute w
AA = 10
Aa = 8
aa = 8
Relative iv
10/10 = 1.0
8/10 = 0.8
8/10 = 0.8
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Modeling natural selection...
Allele frequencies among gametes
Genotype frequencies among zygotes
Genotype frequencies among surviving adults
2
2
wpop = P WAA + 2 pqwAa + q waa
Allele frequencies among mating adults
Genotype frequencies among offspring
AA = ZP
2
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AA
=
Wpop
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Aa = PQWta
w pop
aa =
<
vv
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2 Patterns of natural selection
Strength of selection (selection coefficients)
Allele frequencies
Dominance relationships
Heterozygotes & Homozygotes
Frequency dependence (positive & negative)
Interactions with other evolutionary forces (coming up…) Strength of selection – selection coefficients
Time to fixation
s = 0.2
s = 0.2
Selection scheme
s = 0.02
Strong
Percent surviving
8;8; 8782
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Weak
s = 0.02 Emerging Infectious Diseases • Vol. 10, No. 3, March 2004
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Antibiotic
Selection Pressure
and Resistance in
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Macrolide use (DDD/ 1, 000 pop/ day )
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Macrolide use (DDD/1,000 pop/ day )
PtgurB 2. A Relationship between macro.de use In the outpatient setting (honzonlal axis) are) prevalence ol macrOtde-resistant
Streptococcus pneumoniae ( vertical arcs) in 16 industrialized countries A regression line was Titled with 95% confidence bands (r * 0 88;
p < 0 001 ) B. Relationship between macrolide use m trie outpatient setting (Horizontal axis) and prevalence of macrobde-resistant S.
pyogenes (vertical axis) in 14 industrialzed countries A regression ine was fitted with 95% confidence bands (r 0.71; p •0 004).
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Total antibiotic use (DDD/ 1,000 pop/ day )
Figure 1. Total antibiotic use in the outpatient setting (vertical axis)
versus prevalence of penicillin-nonsusceptible Streptococcus
pneumoniae (horizontal axis) in 20 industrialized countries , A
regression line was fitted with 95% confidence bands (r = 0.75; p
< 0.001). Dominance relationships interact with allele frequencies
(a) Selection against a recessive allele and for a dominant allele
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Fraction surviving:
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Generation
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An adaptive landscape graphs the mean fitness of a
population as a function of allele frequency
– where is a population is heading –
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Frequency of A
1.0 Dominance relationships interact with allele frequencies
(b) Selection for a recessive allele and against a dominant allele
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Equilibrium
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Sickle cell anemia
Malaria (Plasmodium falciparum)
Normal RBC (A)
Vector-borne infectious disease
caused by protozoan parasite
Sickled RBC (S)
Complex life cycle: reproduces
inside human RBCs
Critical public health concern
Normal
A/A
Susceptible to malaria
Slightly afflicted by SCA
A/S
Slightly protected from malaria
Afflicted by SCA
S/S
Protected from malaria Ward Watt, Colias butterflies
Phosphoglucose isomerase (PGI) plays a key
role in allocating carbohydrates among
biochemical pathways
Butterflies are ectothermic & fly only when body
temperature is high
Selection should favor PGI variants with high
catalytic efficiency (i.e., those that enable
butterflies to metabolize glucose efficiently &
allow them to fly quickly)
Allozymes differ in their functional properties &
are correlated with the prevalence of genotypes
in different environments
Do the allozyme alleles affect the
fitness of Colias butterflies?
Colias meadii (high elevation sp.)
alleles 2, 3 common
2/2 & 2/3 relatively high
activity @ low temps., but
lose activity @ high temps.
Tested enzyme activity of
genotypes @ various
temperatures (10–50°)
heterozygous genotypes (esp.
3/4) had high efficiencies
alleles 3, 4 common
Colias philodice, C. eurytheme (lower elevations) Allozymes differ in their functional properties &
are correlated with the prevalence of genotypes
in different environments
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Do the allozyme alleles affect the
fitness of Colias butterflies?
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Given biochemistry, 3/4 genotypes should…
(1) fly more frequently
(2) fly a greater span of the day
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babies & genotyped all offspring
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Frequency p of A allele
1
Frequency p of A \ allele Positive frequency dependence
Heliconius erato
Unpalatable species with many distinctive geographic varieties,
each variety is monomorphic
Adjacent varieties breed in zones only a few kilometers wide
!
Predators learn to avoid butterflies of the most COMMON pattern, but
attack (eat?) butterflies of UNCOMMON patterns they do not recognize Negative frequency dependence
Frequency-Dependent Natural Selection in the
Handedness of Scale-Eating Cichlid Fish
SCIENCE
•
VOL. 260
•
9 APRIL 1993
Right-handed (dextral)
feed on LEFT flank of prey
Left-handed (sinistral) feed
on RIGHT flank of prey
Four tenets of natural selection…
(1)! Individuals within populations are variable
(2)! Variation is heritable
(3)! Organisms differ in their ability to survive and reproduce
(4)! Survival & reproduction are non-random Dactylorhiza sambucina
Pollinated by bumblebees, but flowers are rewardless
Orchids make pollinia (making pollen unavailable) &
there is no nectar
– pollination by deceit –
5
7
3
2
1
4
6
What does such movement mean for the number
of times each type (color) is visited?
On average, which morph will receive more visits?
How will such visitation affect fitness? Relative male reproductive success
P)
0
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Relative female reproductive success
P
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b Probability of survival
Number
Contrasting selection
can maintain genetic
diversity
Number
Multiple niches & polymorphism
Lower mandible width (mm) 13.3°C I
8.9°C|
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0 - 4.4°Cl
White indicates
proportion of plants
not
producing cyanide
Red indicates
proportion of plants
producing cyanide
^
o
Natural selection - Coursework Materials
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