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BIOL 4120: Principles of Ecology
Lecture 6: Evolution and
Adaptation
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: [email protected]
Introduction
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Major question in Ecology: What determines
distribution & abundance of species?
Two classes of answers
• Contemporary, local and regional factors
(biomes and PPT and T)
• Historical factors (= evolutionary ones)
 Why different species live in different
environments? (Adaptation and
evolution)
 E.g., grasslands; long necked giraffe in
savannas of Africa (widely dispersed,
umbrella-shaped trees); white coated
polar bear in Arctic (invisible to prey)
Evolutionary Ecology (Chapter 6)
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6.1 Phenotype is the outward expression of
an individual’s genotype
6.2 Adaptations result from natural selection
on heritable variation in traits that affect
evolutionary fitness
6.3 Evolutionary changes in allele frequencies
have been documented in natural populations
6.4 Individuals can respond to their
environments and increase their fitness
6.5 Phenotypic plasticity allows individuals to
adapt to environmental change
6.1 Phenotype is the outward
expression of an individual’s
genotype
Review concepts in Genetics:
1. Gene and genetic variation
2. Phenotype and genotype
3. Sources of genetic variation
4. Qualitative and quantitative traits
What are genes?
Genes: discrete subunit of chromosome,
carry genetic information
Chromosomes: the threadlike structures
where DNA is contained
DNA: Deoxyribonucleric acid. All DNA is
composed of the same 4 nucleotide (ATGC),
differ in sequence.
Alleles: different forms of a gene (A, a).
Locus: the position of an allele occupies on a
chromosome
Homozygous (AA, aa) vs heterozygous (Aa)
Dominance (A vs a), incomplete dominance
(Aa shows different trait to AA or aa)
How are genes transmitted?
Genotype: the sum of
genes carried by the
individual.
Gene pool: total
collection of genes
across all individual in
the population at any
one time
Phenotype: the
observed expression
of genotype (color etc)
Phenotypic plasticity
Phenotypic plasticity: the capability of an individual to exhibit
different responses and produce a range of phenotypic
expressions under different environmental conditions.
Sources of genetic variation
Genetic variation within a population is
absolutely necessary for natural selection to
occur
If all individuals are identical within a
population then their fitness will all be the
same
Sources of genetic variation
• Mutation: inheritable changes in a gene or a chromosome
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Gene mutation: (point mutation)
fibrosis
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Chromosome mutation
such as sickle-cell anemia, cystic
• deletion, duplication, inversion, translocation
• Genetic recombination
Sexual reproduction
two individuals produce haploid gametes (egg or sperm) – that
combine to form a diploid cell or zygote.
• Reassortment of genes provided by two parents in the offspring
• Increases dramatically the variation within a population by
creating new combinations of existing genes.
Asexual reproduction: less variation (only mutation)
Genetic basis of continuously
varying phenotypic traits
Many phenotypic traits show continuous variation (quantitative traits).
Traits such as sizes and rates of processes are often influenced by many
genes.
6.2 Adaptation result from natural
selection on heritable variation in
traits that affect evolutionary fitness
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Evolution pertains to any changes in a population’s
gene pool. When genetic factors cause differences
among individuals in survival and reproductive
success, evolutionary change comes about through
natural selection. Individuals whose traits enable
them to achieve higher rates of reproduction leave
more descendants, and therefore the alleles
responsible for those traits increase in the gene
pool of the population.
The process is often referred to as Adaptation.
Evolution by natural selection
What is Darwin’s natural selection?
The differential success (survival and
reproduction) of individuals within the
population that results from their interaction
with their environment.
“Survival of fitness, elimination of
‘inferior’ individual”
Three main ingredients of evolution by
natural selection:
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1. There is variation among individuals in a
population.
2. The Variation is heritable.
3. Differences in survival and reproductive success,
or fitness, related to that variation.
Survival and reproduction are not random, but are
related to variation among individuals. Organisms
with best characteristics are ‘naturally selected.’
If 3 conditions are met, the population will change
from one generation to the next. Evolution will
occur.
One example:
Evolutionary change in a
population may result from a
change in the environment.
Cyanide fumigation to kill scale
insects
Initially, very effective, killed
most non cyanide-resistant
individuals
Fumigation was not effective
Natural and artificial selection
(crops, domestic animals)
Evidence of natural selection
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Evolution of beak shape in Finches.
Peter and Rosemary Grant’s (and
colleagues) work on Medium Ground
Finch Geospiza fortis.
Natural
selection
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Darwin’s
Finches
Genetic
studies show
all arise from
a single
ancestral
species.
40-ha Daphne
Major island
Rosemary & Peter Grant
Is there a phenotypic variation in
beak size?
Is variation in beak size correlated with
variation in fitness?
In 1978, there was a
severe drought due to
La Nina, small seeds
declined more than
large seeds.
Small beak birds have
difficulty to find seeds,
and suffered heavy
mortality, especially
females.
post-drought
pre-drought
Beak size evolves
Conclusion: Nature selection indeed caused evolution in
beak size
Three types of selection
Disruptive selection increases
phenotypic variation in a
population
Black bellied seedcraker
6.3 Evolutionary changes in allele
frequencies have been documented in
natural populations
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Cyanide resistance in scale insects
Pesticide and herbicide resistance
among agricultural pests
Antibiotic resistance among
pathogenic bacteria (superbug)
Selection and change in frequency of
melanistic moths
Birds eaten
Normal Melanistic
Unpolluted woods
Polluted
woods
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Kettlewell (1950s)
Early in the nineteenth century, occasional dark, or melanistic,
speciemens of the peppered moth were collected. Over the next
hundred years, this dark form became increasing common in forests
near heavily industrialized region  industrial melanism.
England, started
pollution control
in the 1950s
6.4 Individuals can respond to
their environments and increase
their fitness
Evolution occurs through the replacement of less fit individuals by the
progeny of more fit individuals in a population over time.
Individuals do not benefit from evolution. It is the gene pool of
the population evolves, not individuals.
But individuals can undergo certain changes over space and time and
respond to the environmental changes.
E.g.: Global change or urbanization.
Animal: can move around.
Microhabitaes and microenvironments.
Example: Responses of Catcus wren to microhabitats.
BIOL 4120: Principles of Ecology
Lecture 6: Evolution and
Adaptation
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: [email protected]
Recap
Evolution by natural selection
Example of national selection: Beak size
Three types of selection
Individuals can respond to environmental
changes
6.5 Phenotypic plasticity allows
individuals to adapt to
environmental change
The set of phenotype
expressed by a single
genotype across a range
of environmental
conditions is referred to as
the norm of reaction
Reaction norm.
Norm of reaction
The set of phenotype expressed by a single genotype across a
range of environmental conditions is referred to as the norm of
reaction.
The reaction norms of
populations adapted to
different environments
may differ
Caterpillars of
swallowtail butterfly
were obtained from two
populations: one from
Alaska and one in
Michigan. Grow in two
temperature conditions
High T stimulated
growth, but in cold T,
caterpillars from Alaska
grow better under lower
T.
Norm of reaction
Reaction norms may be modified by
evolution
Reaction norms may
diverge when two
populations of the
same species exist
for long periods
under different
conditions. Very
often, an increase in
performance under
prevalent conditions
is accompanied by a
decrease in
performance when
exposed to
conditions outside
the population’s
normal range .
Acclimation
Adaptive phenotypic plasticity referred to as
Acclimation, such as growing thicker fur in winter,
producing smaller leaves during the dry season,
producing enzymes with different T optima at different
temperatures.
Acclimation may be thought as a shift in an individual’s
range of physiological tolerances. It is useful in
response to seasonal and other persistent changes in
conditions
Acclimation may takes days to weeks
Acclimation is reversible
Blue: 20oC
Red: 45oC
Larrea: creosote bush, subtropical desert plant, photosynthesis in both
winter and summer
Atriplx: saltbush, native to cool coastal region of CA
Irreversible developmental responses
Development responses:
When conditions persist for long
periods, the environment may
influence individual development
so as to modify the size or other
attributes of the individual for
long periods, even for its
remaining life time. These
changes are referred to as
Development Responses
Coloration of African grasshopper
Development responses are not reversible
Water fleas
Left was exposed to
predators and
survived, with a
helmet.
Genotype-environment interaction
Phenotypes = Genotypes + Environments
How to test if phenotypic variation is due to
genotype or environments?
Reciprocal transplant experiments
Reciprocal transplant experiment are used to
investigate the causes of differences between
populations
The growth rate of fence lizards reveal both genetic
determination and phenotypic plasticity
The End