Download VI. Levels of Selection

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.
VI. Levels of Selection
Selection can occur wherever there is differential reproduction among variable
entities.
A. Gene Selection
1. Meiotic Drive:
2. Transposable Elements
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
3. 'Selfish' Genes (Richard Dawkins)
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
rb > c
…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)
F. Group Selection (Wynne-Edwards)
- Can groups replace one another simply by reproductive success??
F. Group Selection (Wynne-Edwards)
- Can groups replace one another simply by reproductive success??
- First, it would have to be recognized by it's contradiction with organismal
selection.
F. Group Selection (Wynne-Edwards)
- Can groups replace one another simply by reproductive success??
- First, it would have to be recognized by it's contradiction with organismal
selection.
- (Sacrifice of fitness at the organismal level with increase at the level of the
group).
F. Group Selection (Wynne-Edwards)
- Can groups replace one another simply by reproductive success??
- First, it would have to be recognized by it's contradiction with organismal
selection.
- (Sacrifice of fitness at the organismal level with increase at the level of the
group).
- Altruism is a possible example - sacrifice reproduction for benefit of the group...
but it usually doesn't work because f(altruism) declines within the pop if
organisms are unrelated!
F. Group Selection (Wynne-Edwards)
- But – there are caveats with kin selection, too
Naked mole-rats:
• Live for 31 years
• Don’t get cancer; division inhibited by cellcell contact, and have an odd hyaluronan
protein…5x larger than humans and
cancer-prone species in which the normal
form increases rate of metastasis.
• MUCH lower mutation rate
• Only mammals that are
thermoconformers
• Eusocial: one ‘queen’, 2-3 males, the rest
sterile workers in two size castes.
• “Vertebrate of the Year” in 2013
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
- Selection for sexually reproducing species:
Parthenogenesis arises spontaneously, but extinctions are rapid due to lack of
variation and Muller's rachet.
Muller's ratchet is the continuous accumulation of mutations in a lineage.
In sexual reproduction, since only 1/2 of the genes are passed from each parent,
there is a 50% chance that a deleterious new mutation will be purged from the
genome just by chance. And also, even if it is expressed, there will be other
organisms in the pop that did NOT receive it and have higher fitness. So,
selection can purify this sexual population of the deleterious alleles.
But in an asexual lineage, all offspring get the whole genome - even a new
deleterious allele. So, there is no way to purge it from the genome.
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:
- Parthenogenesis arises spontaneously, but extinctions are rapid due to lack of
variation and Muller's rachet.
So, extinction rates in parthenogenetic lineages are high... and so most lineages
that radiate and produce lots of descendant species are sexual.
G. Species Selection
- Selection for sexually reproducing species:
- Certain lineage are more likely to speciate (beetles - small, tough, and easily
isolated...)
G. Species Selection
- Selection for sexually reproducing species:
- Certain lineage are more likely to speciate (beetles - small, tough, and easily
isolated...)
SO, as a consequence of survival and speciation rate (reproduction), sexual
lineages and also more rapidly speciating lineages will leave more species and
replace other lineages that die out over time.