IV. Variation in Quantitative Traits

1
IV. Variation in Quantitative Traits A.
Quantitative Effects B. Partitioning Variance
C. Selection on Quantitative Traits - Traits
affected by many genes have a higher probability
of including a pleiotrophic gene a gene that
affects more than one trait. So, we might expect
complex, quantitative traits to be CORRELATED to
other traits. If selection is acting on both
traits in different ways, neither will be
optimized. Adaptations will be a compromise,
depending on the relative strengths of the
selective pressures, the relative values of the
adaptive traits, and their heritabilities (ease
with which they can respond to selection).
2
Consider the Grants work on medium ground
finches during the drought of 76-77. Birds
with deep and narrow beaks had the greatest
fitness.
3
Consider the Grants work on medium ground
finches during the drought of 76-77. Birds
with deep and narrow beaks had the greatest
fitness. But beak depth and beak width are
POSITIVELY CORRELATED (probably developmentally).
4
Consider the Grants work on medium ground
finches during the drought of 76-77. Birds
with deep and narrow beaks had the greatest
fitness. But beak depth and beak width are
POSITIVELY CORRELATED (probably developmentally).
So, although selection should have pushed the pop
along the blue line, it went along the green
line, because there is greater benefit to a deep
bill rather than a narrow bill.
5
IV. Variation in Quantitative Traits A.
Quantitative Effects B. Partitioning Variance
C. Selection on Quantitative Traits D.
Selection and Genetic Variation
6
IV. Variation in Quantitative Traits A.
Quantitative Effects B. Partitioning Variance
C. Selection on Quantitative Traits D.
Selection and Genetic Variation - modes of
selection and phenotypic variation
7

• modes of selection
• - directional changes the mean phenotype and
  tends to reduce variation.

8

• modes of selection
• - stabilizing does not change the mean but
  reduces variation.

9

• modes of selection
• - disruptive does not change the mean but
  increases variation.

10
Directional
11
Stabilizing
12
Disruptive
African seedcrackers disruptive selection due to
efficiencies on large or small seeds.
13
D. Selection and Genetic Variation - modes of
selection and phenotypic variation if most
selection is directional and stabilizing, then
variation is reduced including genetic variation
(these are quantitative traits, not single genes
maintained by heterozygote advantage at one
locus).
14
D. Selection and Genetic Variation - modes of
selection and phenotypic variation if most
selection is directional and stabilizing, then
variation is reduced including genetic variation
(these are quantitative traits, not single genes
maintained by heterozygote advantage at one
locus). But, even for very adaptive traits,
there is usually still phenotypic and genetic
variation. Why?
15
D. Selection and Genetic Variation - modes of
selection and phenotypic variation - sources
of variation - new adaptive mutations are
constantly produced and are increasing in
frequency in the population.
16
D. Selection and Genetic Variation - modes of
selection and phenotypic variation - sources
of variation - new adaptive mutations are
constantly produced and are increasing in
frequency in the population. - deleterious
mutations are maintained at low frequency
especially for genes contributing to quantitative
traits where the selective pressure on any one
locus may be weak.
17
D. Selection and Genetic Variation - modes of
selection and phenotypic variation - sources
of variation - new adaptive mutations are
constantly produced and are increasing in
frequency in the population. - deleterious
mutations are maintained at low frequency
especially for genes contributing to quantitative
traits where the selective pressure on any one
locus may be weak, or recessive alleles. -
disruptive, frequency dependent, multiple niche
polymorphisms, etc., in which the adaptive value
of existing alleles changes through time or
across space within the population.
18
IV. Variation in Quantitative Traits V. Selection
and Adaptation
19
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions
20
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions - selection
differential reproductive success
21
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions - selection
differential reproductive success - fitness
reproductive success
22
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions - selection
differential reproductive success - fitness
reproductive success - adaptation a trait or
suite of traits that increases reproductive
success.
23
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions - selection
differential reproductive success - fitness
reproductive success - adaptation a trait or
suite of traits that increases reproductive
success. - exaptation an adaptation
co-opted for a new function. (flight feathers are
an exaptation of thermoregulatory feathers, which
may be an exaptation of feathers initially
adaptive as sexual ornaments).
24
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues
25
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues -
all traits are NOT adaptations spandrels of
San Marco (Gould and Lewontin) even if we can
envision a function for them.
26
(No Transcript)
27
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues -
all traits are NOT adaptations spandrels of
San Marco (Gould and Lewontin) even if we can
envision a function for them. - some are due
to drift in different populations - some are
correlated or linked to adaptive genes
28
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues C. How
do we identify adaptations?
29
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues C. How
do we identify adaptations? 1. Experiment
30
Zonosemata flies (Family Tephritidae) wave their
banded wings when threatened. Why?
31
Zonosemata flies (Family Tephritidae) wave their
banded wings when threatened. Are they mimicking
spiders to deter other predators, mimicking
spiders to deter spider predators, or does it
have nothing to do with predation? (Waving for
courtship?)
32
(No Transcript)
33
Housefly..no waving
34
Responses of other preds.
35
ALL EATEN!!!
36
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues C. How
do we identify adaptations? 1. Experiment 2.
Observational Studies - Do desert lizards
thermoregulate behaviorally? can define the
physiological relationships between temp and
metabolism and activity in the lab, but do they
choose areas that maintain their temp in this
range? Go look in an environment with variable
temps, and see if choice meets the adaptive
expectation.
37
Natural distribution
38
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues C. How
do we identify adaptations? 1. Experiment 2.
Observational Studies 3. Comparative Method
39
In some species of bats, males have
disproportionately large testis. And some
evolutionary biologists are interested in knowing
why. Is it related to sperm competition and
social group size? - Females in larger groups
would have the chance to mate with more males, so
there would be greater benefit to producing more
sperm
40
Looks good, but..!
41
Data points need to be independent, and these are
NOT phylogenetically independent if we make them
so, the data set decays to just two points... Not
too conclusive.
42
Compare sister taxa When divergence occurs, does
the one with a bigger social group have big
testes?
43
Compare sister taxa When diverge occurs, does
the one with a bigger social group have big
testes? Then, slide each relationship to the
origin, standardizing the divergence to 0. Are
the endpoints correlated? This controls for
phylogenetic correlations.
44
Hosken 1998
45
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues C. How
do we identify adaptations? D. Constraints on
the POWER of selection - physical
constraints why do flying fish return to
water?
46
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues C. How
do we identify adaptations? D. Constraints on
the POWER of selection - physical
constraints - contradictory selective
pressures Leaf size
47
Photosynthetic Potential
Water retention
Leaf Size
48
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues C. How
do we identify adaptations? D. Constraints on
the POWER of selection - physical
constraints - contradictory selective
pressures - historical constraints (extant
genome, physiology, anatomy, behavior)
49
IV. Variation in Quantitative Traits V. Selection
and Adaptation A. Definitions B. Issues C. How
do we identify adaptations? D. Constraints on
the POWER of selection - physical
constraints - contradictory selective
pressures - historical constraints (extant
genome, physiology, anatomy, behavior) - lack
of genetic variation
50
IV. Variation in Quantitative Traits V. Selection
and Adaptation VI. Levels of Selection
51
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities.
52
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection
53
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive
54
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive In some organisms, the
heterozygote produces a preponderance of one
gamete type - this is called "segregation
distortion". This gene is at a selective
advantage over other genes at this locus. Of
course, as it increases in frequency and more
organisms are homozygous for it, the differential
reproduction drops. However, this can be balanced
by the reduced number of gametes these organisms
produce.
55
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive In some organisms, the
heterozygote produces a preponderance of one
gamete type - this is called "segregation
distortion". This gene is at a selective
advantage over other genes at this locus. Of
course, as it increases in frequency and more
organisms are homozygous for it, the differential
reproduction drops. However, this can be balanced
by the reduced number of gametes these organisms
produce. An example is the t-allele in mice.
Heterozygotes only produce gametes with the 't'
allele - no 'T' gametes.
56
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive In some organisms, the
heterozygote produces a preponderance of one
gamete type - this is called "segregation
distortion". This gene is at a selective
advantage over other genes at this locus. Of
course, as it increases in frequency and more
organisms are homozygous for it, the differential
reproduction drops. However, this can be balanced
by the reduced number of gametes these organisms
produce. An example is the t-allele in mice.
Heterozygotes only produce gametes with the 't'
allele - no 'T' gametes. However, the rise in
frequency of the 't' allele is balanced at the
organismal level by selection against the
homozygote - 'tt' is lethal. So, the allele can
not increase in frequency and is dependent upon
other alleles in the population.
57
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive

• - Stalk-eyed flies, Cyrtodiopsis dalmanni
• (Presgraves, et al.1997).
• X(d) meiotic drive element on the X chromosome
  causes female-biased sex ratios in natural
  populations of both species.

58
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive

• - Stalk-eyed flies, Cyrtodiopsis dalmanni
• (Presgraves, et al.1997).
• X(d) meiotic drive element on the X chromosome
  causes female-biased sex ratios in natural
  populations of both species.
• spermatid degeneration in male carriers of
  X(d).

59
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive

• - Stalk-eyed flies, Cyrtodiopsis dalmanni
• (Presgraves, et al.1997).
• X(d) meiotic drive element on the X chromosome
  causes female-biased sex ratios in natural
  populations of both species.
• spermatid degeneration in male carriers of
  X(d).
• balanced by Y-linked and autosomal factors that
  decrease the intensity of meiotic drive.

60
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive

• - Stalk-eyed flies, Cyrtodiopsis dalmanni
• (Presgraves, et al.1997).
• X(d) meiotic drive element on the X chromosome
  causes female-biased sex ratios in natural
  populations of both species.
• spermatid degeneration in male carriers of
  X(d).
• balanced by Y-linked and autosomal factors that
  decrease the intensity of meiotic drive.
• Even a Y-linked polymorphism for resistance to
  drive which reduces the intensity and reverses
  the direction of meiotic drive.

61
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive

• - Stalk-eyed flies, Cyrtodiopsis dalmanni
• (Presgraves, et al.1997).
• X(d) meiotic drive element on the X chromosome
  causes female-biased sex ratios in natural
  populations of both species.
• spermatid degeneration in male carriers of
  X(d).
• balanced by Y-linked and autosomal factors that
  decrease the intensity of meiotic drive.
• Even a Y-linked polymorphism for resistance to
  drive which reduces the intensity and reverses
  the direction of meiotic drive.
• When paired with X(d), modifying Y chromosomes
  (Y(m)) cause the transmission of predominantly
  Y-bearing sperm, and on average, production of
  63 male progeny.

62
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive 2. Transposable Elements
63
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive 2. Transposable Elements these
genes replicate themselves independently of cell
division... they are gene parasites that make
nothing for the cell. yet they increase in
frequency relative to other genes in the genome.
64
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive 2. Transposable Elements 3.
'Selfish' Genes (Richard Dawkins)
65
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive 2. Transposable Elements 3.
'Selfish' Genes (Richard Dawkins) - genes are
the fundamental replicators
66
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive 2. Transposable Elements 3.
'Selfish' Genes (Richard Dawkins) - genes are
the fundamental replicators - genes which
confer an advantage, when averaged across other
genetic backgrounds, will be selected for.
(Analogy of 'crews')
67
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection 1.
Meiotic Drive 2. Transposable Elements 3.
'Selfish' Genes (Richard Dawkins) - genes are
the fundamental replicators - genes which
confer an advantage, when averaged across other
genetic backgrounds, will be selected for.
Analogy of 'crews') - co-adaptive assemblages
and non-additive effects are not explained
68
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection
69
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection - some mitochondria in
yeast are non-respiring parasites - they survive
but don't produce much energy for the cell. They
reproduce fast in a cell.
70
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection - some mitochondria in
yeast are non-respiring parasites - they survive
but don't produce much energy for the cell. They
reproduce fast in a cell. - In small populations
of yeast, where selection at the organismal level
is weak, there is no cost to the cell to
reproducing slowly and the parasitic mitochondria
dominate within cells.
71
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection - some mitochondria in
yeast are non-respiring parasites - they survive
but don't produce much energy for the cell. They
reproduce fast in a cell. - In small populations
of yeast, where selection at the organismal level
is weak, there is no cost to the cell to
reproducing slowly and the parasitic mitochondria
dominate within cells. - In large populations,
where aerobic respiration is advantageous at a
cellular level, cells with parasites are selected
against and the frequency of parasitic
mitochondria is reduced.
72
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection - some mitochondria in
yeast are non-respiring parasites - they survive
but don't produce much energy for the cell. They
reproduce fast in a cell. - In small populations
of yeast, where selection at the organismal level
is weak, there is no cost to the cell to
reproducing slowly and the parasitic mitochondria
dominate within cells. - In large populations,
where aerobic respiration is advantageous at a
cellular level, cells with parasites are selected
against and the frequency of parasitic
mitochondria is reduced. - There is a balance of
selection at different levels that must be
understood to explain the different frequency of
parasitic mitochondria.
73
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection C. Cell Selection
74
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection C. Cell Selection -
Cancerous Tumour - cell division increases, and
the effects may be balanced at a higher level
(organism).
75
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection C. Cell Selection D.
Organism Selection (Darwinian)
76
VI. Levels of Selection Selection can occur
wherever there is differential reproduction among
variable entities. A. Gene Selection B.
Organelle Selection C. Cell Selection D.
Organism Selection (Darwinian) E. Group
Selection
77
Nowak, M. A. 2006. Five rules
for the evolution of cooperation. Science
3141560-1563.
Pseudomonas flourescens
Colonies with high concentration of mat-builders
(expensive proteins) float if cheaters increase
in number, colony sinks and dies.
78
(No Transcript)