Chapters 1

1
Chapters 12

• Principles of evolution
• Natural Selection

2
The paradigm of biology

• Evolution is the paradigm of modern biology
• A paradigm is a set of fundamental principles in
  a particular field that governs how every
  scientist views the world
• At any given time, the paradigm represents the
  consensus of all working scientists on the known
  truths about the physical world.

3
Evolution ecology

• "The Ecological Theatre and the Evolutionary
  Play"
• Evolution by natural selection is always guided
  by the ecological setting in which a population
  occurs.
• Darwin was the first real ecologist!
• Much of what ecologists study is meaningful only
  in the context of evolution

4
Evolution natural selection

• Definition of evolution
• Evolution is genetic change in a population over
  time.
• Specifically
• Evolution is the change
• in allele frequencies in a population
• alleles different versions of each gene
• as individuals possessing those alleles
• are born, die or disperse.

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The Genetic Code

• Genes are composed of nucleotide sequences along
  DNA molecules.
• Cytosine,Guanine,Thymine,Adenine
• C,G,T,A are letters in the genetic language
• Together three nucleotides code for each amino
  acid in a protein and for the regulation of genes
• A gene codes for a trait or characteristic
• A gene is a word in the genetic language
• All the genes (genome) make up a book of
  instructions on how to make 1 individual organism

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(No Transcript)
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DNA provides instructions for all cellular
functions
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Genetic terminology

• The position of the nucleotide sequence trait
  of a gene on the chromosome is called its locus
  (plural loci).
• Most organisms have pairs of chromosomes with the
  same overall gene loci (i.e, two copies of each
  gene). (diploid)
• Different forms (different nucleotide sequences)
  for the same genes are termed alleles.
• Alleles are created by mistakes in the
  transcriptions of genesthese mistakes are called
  mutations.
• These features of the genetic code lead to
  genetic variation among individuals

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Examples of traits determined by different alleles
http//www.athro.com/evo/gen/inherit1.html
The genetic instructions for eye color are
simple 2 loci/2 alleles.
The genetic instructions to make an eye are very
complex! They involve dozens if not hundreds of
genes.
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Phenotypic vs. genotypic variation

• Genotypic variation differences in the genetic
  makeup of individuals cause
• Phenotypic variation differences in the
  expression of genes--
• morphological, physiological or behavioral
  characteristics between different individuals in
  a population.

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What genetic phenotypic variation in a
population looks like
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Picture of population variation
13
Sources of genetic variation

• Mutation a change in the sequence or structure
  of a gene.
• SEX
• Recombination of chromosomal segments during
  meiosis (Fig. 1.9) leading to new combinations of
  alleles on chromosomes.
• The shuffling of chromosomes with gamete
  formation and fertilization.

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Evolution happens

• When the frequencies (relative numbers) of
  alleles at different loci change with time in a
  population
• HOW?
• Mutation
• think about this for a minute

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Allele frequencies
Aa aa Aa AA Aa aa Aa Aa AA AA aa Aa
AA AA AA Aa AA aa Aa Aa Aa Aa Aa AA aa
aa AA Aa What is the frequency of A and a
alleles?
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Allele frequencies
AA Aa AA AA Aa aa Aa Aa AA AA Aa Aa
AA AA AA Aa AA Aa Aa AA AA Aa AA AA Aa
aa AA Aa Did the frequency of A and a
alleles change?
Generations later..
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Evolution happened

• The frequency of A and a alleles changed with
  time
• specifically over at least one generation (some
  individuals died and new individuals were born)
• What change occurred?
• A or a more frequent than before?

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Mechanisms of evolution

• What causes gene frequencies to change?
• Mutation
• Gene flow
• Genetic drift
• Selection

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Natural selection requires

• a character to be inherited the phenotype of an
  individual must be a result of its genotype.
• genetic variation phenotypic differences among
  individuals must be the result of genotypic
  differences.
• differential reproduction and survival
• genotypic differences between individuals make
  some individuals more likely to survive OR allow
  some individuals to have more offspring than
  others.

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Allele frequencies
AA Aa AA AA Aa aa Aa Aa AA AA Aa Aa
AA AA AA Aa AA Aa Aa AA AA Aa AA AA Aa
aa AA Aa The frequency of A alleles
increased
Generations later..
because more offspring with A alleles survived
and grew up to reproduce.
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Allele frequencies
AA AA AA AA AA AA AA AA AA AA AA AA
AA AA AA AA AA AA AA AA AA AA AA AA AA
AA AA AA The frequency of A alleles
increased even more..
Can evolution occur in this population through
time?
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Results of natural selection

• Adaptation The frequency of alleles enhancing
  survival and reproduction increases in a
  population with time.
• Individuals with traits coded by those alleles
  get more common in a population with time. A
  trait enhancing survival or reproduction can also
  be called an adaptation.
• With environmental change, the frequency of
  alleles can only change if there is more than 1
  type of a gene (more than one allele) in a
  population genetic variation for the trait.

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Allele frequencies
AA AA AA AA AA AA AA AA AA AA AA AA
AA AA AA AA AA AA AA AA AA AA AA AA AA
AA AA AA The frequency of A alleles
increased through time
An A allele promotes survival and
reproduction Adaptation has occurred.
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Adaptation
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Adaptation
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Evolution in Anolis lizards
Jonathan Losos student
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Ecomorphs

• Crown-Giant
• Trunk-Crown
• Trunk
• Twig
• Trunk-Ground
• Grass-Bush

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Evidence that ecomorphs arise from natural
selection
Variation within a species gives the potential
for natural selection Lizards on islands with
larger perches on average have longer hind limbs
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Ecotypes geographically isolated ecomorphs

• When populations become isolated on different
  islands, that have different environments
• Adaptation occurs and results in different
  ecotypes

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Ecotypes

• An ecotype is a locally adapted population
• that is, an ecotype is a population adapted to
  local ecological conditions.
• Ecotypes are more likely to form under three
  conditions

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3 conditions lead to formation of ecotypes

• Geographic variation in environmental conditions.
• Natural selection on a character related to that
  environmental variable
• Limit or barriers to gene flow, so that local
  adaptation is possible

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More examples of ecotypesKiller Whales

• Killer whales are predators of large prey. Like
  wolves they are highly social, live in stable
  groups (pods) and cooperate to hunt.
• These whales are cooperating to kill a dolphin
  (actually they are using the dolphin to teach a
  young killer whale how to capture this prey).

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More examples of ecotypesKiller Whales

• However, killer whales do not all prey on marine
  mammals.
• There are two ecotypes of killer whales
• Fish-eating killer whales
• Marine-mammal eating killer whales
• What do you think maintains the ecotypes?

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Killer whale ecotypes

• What conditions maintain the two killer whale
  ecotypes?
• Environmental variation in what?
• Selection on what character?
• What limits gene flow?

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Example of ecotypesDarwins finches (Geospiza)
Chapter 11 13
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The seed eating finches Geospiza
G. fortis
G. fulginosa
Each eat seeds of different sizes
G. magnirostris
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Summary

• Genetic variation allows natural selection to to
  be possible.
• In general, genetic variation is beneficial
  because it allows some offspring to succeed when
  environments change in time and space

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Summary

• Natural selection is the most powerful force
  causing allele frequencies to change with time in
  a population (on average)
• Natural selection arises from the interaction
  between an organisms genotype/phenotype and the
  environment
• Therefore natural selection is intimately related
  to ecology ecological processes.