Conflict

1
The evolution of conflict and cooperation
Lecture in the population biology and population
genetics seminar seriesTom Wenseleers, 2001
2
Major transitions in evolution
Szathmary Maynard Smith

• Gene Genome
• Prokaryotes Eukaryotes
• Genomes Genome-alliances
• (diploidy, sex)
• Unicellularity Multicellularity
• Individual organisms Societies

3
Why cooperate?

• Two approaches
• - game theory cooperation is only a good
  strategy when it has mutual or delayed benefits
  (false altruism)
• - kin selection cooperation also possible when
  it has personal costs, but only when interactants
  are genetically related (true altruism)

4

• Delayed benefitshelpers at the nest
• Young individuals stay at home and help their
  parents raise more offspring, rather than
  breeding themselves. Many birds (including these
  fairy wrens) do this.
• Or, in group-living animals sometimes help raise
  other group members offspring (ostriches, some
  primates).

Altruism? Helpers may gain useful experience in
raising their own offspring or they may have
hopes of inheriting a valuable breeding
territory.
5
Mutual (synergistic) benefits
Wolves hunt in packs and then share their prey.

• Is this altruism?
• All the wolves get a benefit from pack hunting
  they can bring down larger prey. Cooperation is
  increasing each wolfs own fitness.

6

• Reciprocal altruism (Trivers)
• E.g. blood sharing in vampire bats.
• Sharing blood does have costs to the donor.
• But they may hope to get something back the next
  night, they might miss out and the neighbor they
  fed will feed them in return (future benefits).

For reciprocal altruism, you need individual
recognition and enough memory of past encounters
to eliminate freeloaders.
7
Game theory
Von Neumann Morgenstern 1944 Theory of Games
and Economic Behaviour
8
Game theory

• Optimal (rational) behaviour in conflict
  situations?
• players (genes, individuals, groups)
• may each choose a strategy
• Each pairs of strategies is associated with a
  payoff

9
Prisoners dilemma
PAYOFFS

• consequence
• player 1 player 2
  for player 1
• defect cooperate B cooperate
  cooperate B-C
• defect defect 0
• cooperate defect -C

10
Maynard Smith Price 1973
Hawk-dove game

• PLAYER 2

DOVE
HAWK
DOVE
0 -B

• PLAYER 1

HAWK
B -C
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Hawk-dove game
- SYNERGY

• Fitness player 1 w1 B.z1-B.z2-C.z1.z2 z1 en
  z2 phenotypes of players 1 2 (hawk1,
  dove0)
• Advantage of playing hawk depends on what the
  other player does benefit B-C.z2
• At equilibrium B-C.z20, and the ESS is to play
  hawk with a probability of zB/C

12
Hawk-dove game

• Limited degree of cooperation is in this case not
  altruistic!
• It avoids mutual destruction!
• Cf. Mutually Assured Destruction (MAD) in cold
  war

13
True altruism

• Definition
• Reproductive altruism An individual behaves in
  such a way as to enhance the reproduction of
  another individual, at a cost to its own fitness.
• Paradox how can natural selection ever favour
  such behaviour (Darwin) ?

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• True altruism
• Sterile workers in social insects give up all
  reproduction for the benefit of their mother
  queen.
• How can such behaviour be selected?

Mutual or delayed benefits cant account for this
one sterile workers never get to produce any
daughters.
15
Group selection(Wynne-Edwards)

• W-E proposed that individuals in group-living
  species might altruistically restrict their
  reproduction to avoid overpopulation and
  starvation.
• The behavior would be favored because groups
  containing such individuals would survive, while
  groups without them would starve and go extinct.
• In general, an altruist that promotes
  reproduction of its groupmates might be favored.
• But theres a problem with group selection.

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Group with altruists, busily outcompeting all the
other groups.
A
A
Z
Z
Z
A
A
Z
The selfish individuals in the group are getting
the benefit but paying no cost. In the next
generation theyve increased within the group.
Z
A
Z
Z
Z
And now altruists are extinct even though theyve
helped the group.
Z
Z
A
Z
Z
Z
Z
Z
Z
Z
Z
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An important distinction
DNA/Gene the Replicator that actually gets
copied in reproduction.
Organism the Vehicle, a machine built by the
DNA to do the copying.
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Replicators Vehicles (Dawkins)

• Replicators that get copied a lot become more
  common, replacing those that get copied less
  thats just what selection is.
• Traits in the vehicles are favored by selection
  if they help the replicators that code for them
  get copied.
• In other words, you always need to look at gene
  frequency change, not at ecological success.

20
W.D. Hamilton (1936-2000)
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Kin selectionHamiltons Rule (1964)
Relatedness to partner

• r.B gt C

Personal cost
Benefit to partner
This rule predicts when a gene for altruism
should be selected. Prediction cooperation at
high relatedness, conflict at low relatedness.
22
Inclusive fitness

• Hamiltons rule leads us to the idea of inclusive
  fitness

Fitness is not only based on own reproduction but
also depends on the effects on other
individuals, weighted by relatedness.
Inclusive fitness direct fitness (own
reproduction) indirect fitness (reproduction of
others) x relatedness
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Empirical tests

• Reproductive conflicts in insect societies
• - Sex-ratio conflicts
• - Conflicts over male production
• - Conflict over caste fate
• Parent-offspring conflict (Trivers)

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Sex-ratio theory
FisherTrivers Hare

• Trait that has a effect on the production of
  females (F) and a - effect on the production of
  males (M)
• EF.rF gt EM.rM (Hamiltons rule)
• EF mating success of females M EM mating
  success of males F
• ESS FM sex-ratio F/M rF / rM

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Relatedness coefficients in an ant colony.
Social insect colonies

X
C
AB
Workergeneration
BC
AC
0,5
0,5
0,75
0,25
AC BC
A, B
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Calculating relatedness

X
1
C
AB
Relatedness between sisters?Share genes via
father with a chance of 1 x 0.5
0,5
Workergeneration
AC BC
BC
AC
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Calculating relatedness

X
C
AB
Relatedness between sisters?Share genes via
mother with a chance of 0.5 x 0.5
0.5
0,5
Workergeneration
AC BC
BC
AC
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Calculating relatedness

X
1
C
AB
Sisters share genes via father OR mother, so
average chance is1 x 0.5 0.5 x 0.5 0.75
0.5
0,5
0,5
0,75
Workergeneration
AC BC
BC
AC
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Sex-ratio conflicts
Trivers Hare

• Mother queen equally related to sons and
  daughters (rF0.5, rM0.5)
• ? Wants to invest equally in both sexes.
• Workers 3 x more related to sisters than to
  brothers (rF0.75, rM0.25)
• ? Prefer 31 FM sex-ratio
• Parent-offspring conflict !

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• Fratricide in ants
• Often have female biased sex ratios. Indicates
  that sex allocation is controlled by the workers.
  
• Except in slave-making ants slaves have no
  genetic stake in the slave-makers sex-ratio.

Wood ant Formica exsecta faculatative sex-ratio
biasing. Some colonies with single mated queen,
others with double mated queen. Workers only eat
their brothers in colonies headed by a single
mated queen. (Sundström)
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Conflicts over male production

• Workers can also produce own sons rw-son0.5 gt
  rw-brother0.25 ? worker reproduction
• But rQ-son0.5 gt rQ-grandson0.25? queen
  policing
• At mating frequencies gt 2 a worker is less
  related to an average worker produced male than
  to a brother?worker policing (Ratnieks)

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Calculating relatedness
Single mating

Relatedness W-Q produced male
0.25Relatedness W-W produced male 0.375
X
0,5
0,5
0,25
0,75
0,375
0,5
0,5
? no worker policing
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Calculating relatedness
1
2
Treble mating

Relatedness W-Q produced male
0.25Relatedness W-W produced male (1/3) x
0.375 (2/3) x 0.125 0.21
X
3
0,5
0,5
0,25
0,25
1
2
3
0,125
0,375
1
2
3
? worker policing
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• Empirical evidence
• Worker reproduction in monandric species
  (stingless bees, bumble bees, some
  wasps).Worker policing in honey bees
  (polyandrous, mating with 10-15 males).

Worker policing in honey bees (Ratnieks) ?
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• Empirical evidence
• Facultative worker policing in Dolichovespula
  saxonica workers only police in polyandrous
  nests. (Foster Ratnieks)

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Conflict over caste fate
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Conflict over caste fate
Bourke Ratnieks 1999

• Stingless bees
• Colonies are swarm founded and therefore mainly
  need workers, just a few queens.
• But 20 of all females develop as queens. A
  clear excess!

38
Conflict over caste fate
Wenseleers et al. 2002

• Explanation each larva is more related to own
  offspring than to sisters offspring ? larva
  prefers to become a queen herself ?overproduction
  of queens if self determination is possible
• Colony doesnt need so many queens ? mother queen
  and adult workers are selected to prevent excess
  queen production (policing)

39
Melipona bees
HIGH RELATEDNESS
LOW RELATEDNESS
MALES QUEEN
PRODUCED SOME WORKER PRODUCED
GLZ, p lt 0.0006
PREDICTEDESS
Prop. of queens produced
(data are from months with maximum queen
production)
40
Policing of caste fate
stingless bees honey
bees
Self determination
Social determination 20 queen
production 0.005 queen production
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In the 70 Bob Trivers showed that there are also
conflict of interests in the seemingly solid
parent-offspring bond.
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Parent-offspring conflict

• Each offspring would like to favour itself over
  its siblings (r0.5)
• Parent on the other hand would prefer to treat
  all offspring equally (equally related).
• Offspring are selected to be more selfish than
  their parents should be willing to tolerate!

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E.g. intra-uterine conflicts
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Major transitions in evolution

• All the previous also applies at other levels
• E.g. conflicts between genes within cells or
  between cells within multicellular
  organismsintragenomic conflicts

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Intragenomic conflicts

• Forms of intragenomic conflict
• - between genes on homologous chromosomes over
  transmission to gametes (meiotic drive)
• - nucleo-cytoplasmic conflicts over optimal sex
  allocation
• - conflicts between cells over who ends up
  producing the gametes

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Meiotic drive cf. hawk-dove game

• HOMOLOGUE 2

COOPERATE
DRIVE
COOPERATE
-B
0

• HOMOLOGUE 1

DRIVE
B
-C
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But there are differences

• Genes Organisms
• Option to breed no usually
• independently
• Fighting strategy poisoning physical
  aggression
• Type of ESS pure mixed

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Nucleo-cytoplasmatic conflict

• Nuclear genesrF0.5 , rM0.5
• Cytoplasmic genes (mitochondria, some bacterial
  symbionts)rF1, rM0Enhance their own
  transmission if they manipulate their host to
  produce a more female biased sex ratio. Males are
  a dead end.

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Male killing Selective killing of
males. Increases the survival of sisters in the
same brood, who carry copies of the maternal
element. Works through kin selection, cf.
fratricide.
E.g. Ricketssia, Wolbachia and Spiroplasma in
ladybird beetle
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Cytoplasmic male sterility (CMS) In approx. 4
of all hermaphrodite plants. Mitochondrial gene
that benefits the female function by sterilising
the male function. Nuclear genes are selected to
suppress CMS.
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Feminisation Feminisation of genetic males.
Presumably works by suppressing the androgenic
gland.Occurs in woodlice (Wolbachia).
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Induction of parthenogenesis Induction of
asexual reproduction, resulting in an all-female
brood. Occurs in some parasitoid wasps
(Wolbachia).
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Maternal sex-ratio Manipulates her host
(Nasonia) to fertilise more eggs than she is
selected to. Nasonia is haplodiploid, so
fertilised eggs develop as females. Exact
nature of maternal sex ratio is as yet unknown.
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Evolution of multicellularity
Slime molds
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Dilemma cf. caste conflict
EACH CELL WANTS TO BECOME A SPORE
?
SPORE
SOMA CELL
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An experiment
gt1 cloneLOW r
1 cloneHIGH r
DeAngelo et al. 1990
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Strassmann et al. 2001
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Green beard genes ultimate selfish genes
Bb
Bb
Bb
BB
Bb
Bb
Gp-9 allozyme locus
Keller Ross 1998
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The End