Download VI. Levels of Selection

VI. Levels of Selection
Selection can occur wherever there is differential reproduction among variable
entities.
Usually identified by outcomes contradictory to predictions at the individual
level.
VI. Levels of Selection
A. Gene Selection
1. Meiotic Drive (Sandler and Novitski 1957):
‘Tailless’ in mice
VI. Levels of Selection
Selection can occur wherever there is differential reproduction among variable
entities.
A. Gene Selection
1. Meiotic Drive (Sandler and Novitski 1957):
Heterozygous males often produce gametes with unequal frequencies of genes.
In mice:
‘tt’ males die; ‘tt’ females are fine.
95% of sperm from heterozygous males (Tt) = ‘t’ tailless allele.
It is a ‘segregation distortion’ allele.
Natural Selection:
Reduces survival of males
Skews sex ratio
Reduces fecundity of heterozygous males
Should be selected against
Frequency maintained by diff. rep. of gene
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 and C.
whitei (Presgraves, et al.1997).
• X(d) meiotic drive element on the X chromosome
causes female-biased sex ratios
• spermatid degeneration of Y-bearing sperm 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 Ybearing sperm, and on average, production of 63%
male progeny.
X(d) Y
95% X
XY, XY(m)
50:50
X(d)Y(m)
63% Y
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.
VI. Levels of Selection
Selection can occur wherever there is differential reproduction among variable
entities.
A. Gene Selection
1. Meiotic Drive:
2. Transposable Elements
- alter gene expression of other genes
- can induce cancers
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
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')
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
VI. Levels of Selection
Selection can occur wherever there is differential reproduction among variable
entities.
A. Gene Selection
B. Organelle Selection
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.
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.
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.
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.
VI. Levels of Selection
Selection can occur wherever there is differential reproduction among variable
entities.
A. Gene Selection
B. Organelle Selection
C. Cell Selection
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).
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)
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. Kin Selection
1. Darwin’s Dilemma
…bees make me sad…
2. W. D. Hamilton - 1964
- related individuals that help one another increase their OWN fitness, because
their alleles occur within THOSE relatives.
2. W. D. Hamilton - 1964
- related individuals that help one another increase their OWN fitness, because
their alleles occur within THOSE relatives.
a. Inclusive Fitness
several relatives have more of
YOUR genes, cumulatively, than
YOU do!
1/2
1/2
½ + ½ + ½ >1
1/2
1
a. Inclusive Fitness
1/2
1/2
1/2
1
If I save myself…
AAAAAAAAA !!!!!
XX
X X
XX
I save one “set” of my
genes…
1/2
1/2
1/2
1
1
If I save my relatives… I save 1.5 sets of my genes. If this has a
genetic basis, selection will favor altruism among relatives.
What a guy!
…ow…
1/2
1/2
1/2
1/2
1
1/2
1/2
3. Examples
1. Helping among relatives – a function of kin selection
3. Examples
1. Helping among relatives – a function of kin selection
3. Examples
1. Helping among relatives – a function of kin selection
3. Examples
2. Haplodiploidy and Social Insects
W. D. Hamilton – 1964
Hamilton’s Rule:
r*b > c
r = coefficient of relatedness
b = benefit to relatives
c = cost to donor
…bees make me sad…
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. Kin Selection
F. Group Selection (Wynne-Edwards)
VI. Levels of Selection
Selection can occur wherever there is differential reproduction among variable
entities.
C. Altruism
Among non-relatives
F. Group2.Selection
(Wynne-Edwards)
Group Selection
Bacterial mats composed of:
individuals that make proteins that help colony float
“cheaters” that spend energy on their own reproduction and not protein production.
Pseudomonas flourescens
Colonies with high concentration
of mat-builders (expensive
proteins) float; if cheaters
increase in number, colony sinks
and dies.
Problem:
To show group selection, distinct from individual selection, it must be shown
that a net ‘cost’ to the individual is outweighed by a net ‘benefit’ to the group,
without invoking relatedness and kin selection.
This is different than an individual benefiting MORE by helping the group than
by acting selfishly. THIS is still maximizing individual fitness.
PRO GROUP: Wilson
ANTI GROUP: Pinker
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. Kin Selection
F. Group Selection (Wynne-Edwards)
G. Species Selection
G. Species Selection
G. Species Selection
Species are analogous to organisms:
births are speciation events
deaths are extinctions
Species that last the longest and spawn the most new species create
evolutionary trends
Speciation rate:
small pops > large pops
Srour, 2012.
Extinction rate:
small pops < large pops
Speciation rate:
Specialized < generalist
G. Species Selection
- Selection for sexually reproducing species:
Parthenogenesis arises spontaneously, but extinctions are rapid due to lack of
variation and Muller's rachet.
In fact, in Daphnia pulex, asexual lineages accumulate deleterious
amino acid substitutions at 4x the rate of sexual lineages (Paland and Lynch
2006, Science 311:990-992).
G. Species Selection
- Selection for sexually reproducing species:
Fig. 1 Maximum likelihood tree of
phylogenetic relationships among
356 species of Solanaceae.
Found that self-incompatible
lineages (turquoise) had
higher rates of speciation
than self-compatible (purple)
lineages.
Emma E. Goldberg et al. Science 2010;330:493-495
Published by AAAS
G. Species Selection
- Certain lineage are more likely to speciate (beetles – character states of:
small, tough, and easily isolated...)