the evolution of conflict and cooperation lecture in the population biology and population genetics...

The evolution of conflict and cooperation

Lecture in the population biology and population genetics seminar series

Tom Wenseleers, 2001

Major transitions in evolution

GenGenee GenomeGenome

ProkaryoteProkaryotess EukaryotesEukaryotes

GenomesGenomes GenomGenome-alliancese-alliances (diploid(diploidyy, sex), sex)

UnicellularityUnicellularity MulticellularityMulticellularity

IndividuIndividuaal organisml organismss SocietiesSocieties

Szathmary & Szathmary & Maynard SmithMaynard Smith

Why cooperate?

Two approaches :Two approaches :

- - game theory:game theory: cooperation is only a good cooperation is only a good strategy when it has mutual or delayed benefits strategy when it has mutual or delayed benefits (false altruism)(false altruism)

- - kin selection:kin selection: cooperation also possible when it cooperation also possible when it has personal costs, but only when interactants has personal costs, but only when interactants are genetically related (true altruism)are genetically related (true altruism)

Delayed benefits:helpers at the nestYoung individuals stay at home and Young individuals stay at home and help their parents raise more help their parents raise more offspring, rather than breeding offspring, rather than breeding themselves. Many birds (including themselves. Many birds (including these fairy wrens) do this.these fairy wrens) do this.

Or, in group-living animals Or, in group-living animals sometimes help raise other group sometimes help raise other group members’ offspring (ostriches, some members’ offspring (ostriches, some primates).primates).

Altruism? Helpers may gain useful experience in raising their own Altruism? Helpers may gain useful experience in raising their own offspring; or they may have hopes of inheriting a valuable breeding offspring; or they may have hopes of inheriting a valuable breeding territory. territory.

Is this altruism?Is this altruism?

All the wolves get a benefit from pack hunting: they can All the wolves get a benefit from pack hunting: they can bring down larger prey. Cooperation is increasing each wolf’s bring down larger prey. Cooperation is increasing each wolf’s own fitness.own fitness.

Mutual (synergistic) benefits

Wolves hunt in Wolves hunt in packs and then packs and then share their prey. share their prey.

For reciprocal altruism, you need For reciprocal altruism, you need individual recognition and enough individual recognition and enough memory of past encounters to memory of past encounters to eliminate freeloaders.eliminate freeloaders.

Reciprocal altruism (Trivers)

E.g. blood sharing in vampire E.g. blood sharing in vampire bats. bats.

Sharing blood does have costs to Sharing blood does have costs to the donor. the donor.

But they may hope to get But they may hope to get something back: the next night, something back: the next night, they might miss out and the they might miss out and the neighbor they fed will feed them neighbor they fed will feed them in return (future benefits).in return (future benefits).

Game theory

Von Neumann & Morgenstern 1944 Von Neumann & Morgenstern 1944 Theory of Games and Economic BehaviourTheory of Games and Economic Behaviour

Game theory

• Optimal (rational) behaviour in conflict Optimal (rational) behaviour in conflict situations? situations?

• ““players” (genes, individuals, groups)players” (genes, individuals, groups)

• may each choose a “strategy”may each choose a “strategy”

• Each pairs of strategies is associated with a Each pairs of strategies is associated with a “payoff”“payoff”

consequenceconsequence player 1 player 1 player 2 for player 1player 2 for player 1

defectdefect cooperatecooperate BB cooperatecooperate cooperatecooperate BB-C-C

defect defect defectdefect 00 cooperatecooperate defect defect -C-C

Prisoner’s dilemma

““PAYOFFS”PAYOFFS”

Hawk-dove game

0 -B

B -C

DOVE HAWK

DO

VE

HA

WK

Maynard Smith & Price 1973

Hawk-dove game

Fitness player 1 wFitness player 1 w11 =B.z =B.z11-B.z-B.z22-C.z-C.z11.z.z22

zz1 1 en zen z22= phenotypes of players 1 & 2= phenotypes of players 1 & 2

(hawk=1, dove=0)(hawk=1, dove=0)

Advantage of playing hawk depends on what the other Advantage of playing hawk depends on what the other

player does: benefit = B-C.zplayer does: benefit = B-C.z22

At equilibrium B-C.zAt equilibrium B-C.z22=0, and the ESS is to play hawk with =0, and the ESS is to play hawk with

a probability of z*=B/Ca probability of z*=B/C

- SYNERGY- SYNERGY

Hawk-dove game

Limited degree of cooperation is in this case not Limited degree of cooperation is in this case not altruistic! altruistic!

It avoids mutual destruction!It avoids mutual destruction!

Cf. “Mutually Assured Destruction” (MAD) in Cf. “Mutually Assured Destruction” (MAD) in cold warcold war

True altruism

Definition :Definition :

Reproductive altruism: An individual Reproductive altruism: An individual behaves in such a way as to enhance the behaves in such a way as to enhance the reproduction of another individual, at a reproduction of another individual, at a cost to its own fitness.cost to its own fitness.

Paradox: how can natural selection ever Paradox: how can natural selection ever favour such behaviour (Darwin) ?favour such behaviour (Darwin) ?

True altruism

Sterile workers in social Sterile workers in social insects: give up all insects: give up all reproduction for the benefit reproduction for the benefit of their mother queen. of their mother queen.

How can such behaviour be How can such behaviour be selected?selected?

Mutual or delayed benefits can’t Mutual or delayed benefits can’t account for this one: sterile workers account for this one: sterile workers never get to produce any daughters.never get to produce any daughters.

Group selection(Wynne-Edwards)

W-E proposed that individuals in group-living W-E proposed that individuals in group-living species might altruistically restrict their species might altruistically restrict their reproduction to avoid overpopulation and starvation.reproduction to avoid overpopulation and starvation.

The behavior would be favored because groups The behavior would be favored because groups containing such individuals would survive, while containing such individuals would survive, while groups without them would starve and go extinct.groups without them would starve and go extinct.

In general, an altruist that promotes reproduction of In general, an altruist that promotes reproduction of its groupmates might be favored.its groupmates might be favored.

But there’s a problem with group selection.But there’s a problem with group selection.

A

AA

A

Z

Z ZZ

Group with altruists, busily outcompeting all Group with altruists, busily outcompeting all the other groups.the other groups.

Z

AZ

A

Z

Z ZZZ

ZZ

Z

Z

Z ZZ

The selfish individuals in the group are The selfish individuals in the group are getting the benefit but paying no cost. In getting the benefit but paying no cost. In the next generation they’ve increased the next generation they’ve increased within the group.within the group.

And now altruists are And now altruists are extinct even though extinct even though they’ve helped the they’ve helped the group.group.

An important distinction

D N AD N A

OrganismOrganism

DNA/Gene: the DNA/Gene: the “Replicator” that “Replicator” that actually gets copied actually gets copied in reproduction.in reproduction.

Organism: the “Vehicle”, a Organism: the “Vehicle”, a machine built by the DNA machine built by the DNA to do the copying.to do the copying.

Replicators & Vehicles (Dawkins)

Replicators that get copied a lot become more Replicators that get copied a lot become more common, replacing those that get copied less: that’s common, replacing those that get copied less: that’s just what selection is.just what selection is.

Traits in the vehicles are favored by selection if they Traits in the vehicles are favored by selection if they help the replicators that code for them get copied.help the replicators that code for them get copied.

In other words, you always need to look at gene In other words, you always need to look at gene frequency change, not at ecological success. frequency change, not at ecological success.

W.D. Hamilton (1936-2000)

Kin selection

Hamilton’s Rule (1964)Hamilton’s Rule (1964)

r.B > C

Relatedness to partnerRelatedness to partner

Benefit to partnerBenefit to partner Personal costPersonal cost

This rule predicts when a gene for altruism should be selected. This rule predicts when a gene for altruism should be selected. Prediction: cooperation at high relatedness, conflict at low relatedness. Prediction: cooperation at high relatedness, conflict at low relatedness.

Inclusive fitness

Hamilton’s rule leads us to the idea of inclusive fitness :

Fitness is not only based on own reproduction but Fitness is not only based on own reproduction but also depends on the effects on other individuals, also depends on the effects on other individuals,

weighted by relatedness. weighted by relatedness.

Inclusive fitness = direct fitness (own reproduction) + Inclusive fitness = direct fitness (own reproduction) + indirect fitness (reproduction of others) x relatednessindirect fitness (reproduction of others) x relatedness

Empirical tests

• Reproductive conflicts in insect societies

- Sex-ratio conflicts

- Conflicts over male production

- Conflict over caste fate

• Parent-offspring conflict (Trivers)

Sex-ratio theory

Trait that has a + effect on the production of females (F) Trait that has a + effect on the production of females (F) and a - effect on the production of males (M) :and a - effect on the production of males (M) :

EEFF..rrFF > E > EMM..rrMM (Hamilton’s rule) (Hamilton’s rule)

EEF F = mating success of females ~ M= mating success of females ~ M

EEM M = mating success of males = mating success of males ~ F~ F

ESS F:M sex-ratio = F/M* = ESS F:M sex-ratio = F/M* = rrFF / / rrMM

FisherFisherTrivers & HareTrivers & Hare

Relatedness coefficients in an ant colony.Relatedness coefficients in an ant colony.

X

0,5 0,50,75 0,25

C AB

ACBC

AC BC

A, B

WorkerWorkergenerationgeneration

Social insect colonies

X

0,5

C AB

ACBC AC BC


Calculating relatedness

1Relatedness Relatedness between sisters?between sisters?

Share genes via Share genes via father with a father with a chance of chance of 1 x 0.51 x 0.5

X

0,5

C AB

ACBC AC BC


0.5Relatedness Relatedness between sisters?between sisters?

Share genes via Share genes via mother with a mother with a chance of chance of 0.5 x 0.50.5 x 0.5


X

0,5

0,750,75

C AB

ACBC AC BC


1

0,5

0.5Sisters share Sisters share genes via father genes via father OR mother, so OR mother, so average chance isaverage chance is

1 x 0.5 + 0.5 x 0.5 = 1 x 0.5 + 0.5 x 0.5 = 0.750.75


Sex-ratio conflicts

• Mother queen: equally related to sons and Mother queen: equally related to sons and daughters (rdaughters (rFF=0.5, r=0.5, rMM=0.5)=0.5)

Wants to invest equally in both sexes.Wants to invest equally in both sexes.

• Workers: 3 x more related to sisters than to Workers: 3 x more related to sisters than to brothers (rbrothers (rFF=0.75, r=0.75, rMM=0.25)=0.25)

Prefer 3:1 F:M sex-ratioPrefer 3:1 F:M sex-ratio

• Parent-offspring conflict !Parent-offspring conflict !

Trivers & HareTrivers & Hare

Fratricide in ants

Often have female biased Often have female biased sex ratios. Indicates that sex ratios. Indicates that sex allocation is sex allocation is controlled by the controlled by the workers. workers.

Except in slave-making Except in slave-making ants: slaves have no ants: slaves have no genetic stake in the genetic stake in the slave-makers sex-ratio. slave-makers sex-ratio.

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

Conflicts over male production

• Workers can also produce own sons Workers can also produce own sons rrw-sonw-son=0.5 > r=0.5 > rw-brotherw-brother=0.25 =0.25 worker reproduction worker reproduction

• But: rBut: rQ-sonQ-son=0.5 > r=0.5 > rQ-grandsonQ-grandson=0.25=0.25

’queen policing’ ’queen policing’

• At mating frequencies > 2 a worker is less related At mating frequencies > 2 a worker is less related to an average worker produced male than to a to an average worker produced male than to a brotherbrother’worker policing’ (Ratnieks)’worker policing’ (Ratnieks)

X

0,5


Relatedness W-Relatedness W-Q produced male = Q produced male = 0.250.25

Relatedness W-Relatedness W-W produced male = W produced male = 0.3750.375

0,5

0,75

0,5

0,25

0,3750,5

Single matingSingle mating

no worker no worker policing policing

X


Relatedness W-Relatedness W-Q produced male = Q produced male = 0.250.25

Relatedness W-Relatedness W-W produced male = W produced male =

(1/3) x 0.375(1/3) x 0.375+ (2/3) x 0.125+ (2/3) x 0.125

= 0.21= 0.21

0,375

0,25

0,5

Treble Treble matingmating

1 2

3

1 2 30,25

1 2 3

0,5

0,125

worker policingworker policing

Empirical evidence

Worker reproduction in monandric species Worker reproduction in monandric species (stingless bees, bumble bees, some (stingless bees, bumble bees, some wasps).wasps).

Worker policing in honey bees Worker policing in honey bees (polyandrous, mating with 10-15 males).(polyandrous, mating with 10-15 males).

Worker policing in honey Worker policing in honey

bees (Ratnieks)bees (Ratnieks)

Empirical evidence

Facultative worker policing in Facultative worker policing in Dolichovespula saxonica Dolichovespula saxonica :: workers only police in workers only police in polyandrous nests. polyandrous nests. (Foster & Ratnieks)(Foster & Ratnieks)

Conflict over caste fate


Stingless beesStingless bees

Colonies are swarm founded and Colonies are swarm founded and therefore mainly need workers, just therefore mainly need workers, just a few queens. a few queens.

But : 20% of all females develop as But : 20% of all females develop as queens. A clear excess! queens. A clear excess!

Bourke & Ratnieks 1999Bourke & Ratnieks 1999

Explanation: each larva is more related to own Explanation: each larva is more related to own

offspring than to sisters’ offspring offspring than to sisters’ offspring

larva prefers to become a queen herself larva prefers to become a queen herself

overproduction of queens if self determination is overproduction of queens if self determination is

possiblepossible

Colony doesn’t need so many queens Colony doesn’t need so many queens mother mother

queen and adult workers are selected to prevent queen and adult workers are selected to prevent

excess queen production (‘policing’)excess queen production (‘policing’)

Wenseleers Wenseleers et al. et al. 20022002


Melipona bees

0

0.05

0.1

0.15

0.2

0.25

MALES QUEEN PRODUCED SOME WORKER PRODUCED

(data are from months with maximum queen production)

Pro

p.

of

qu

een

s p

rod

uced

GLZ, p < 0.0006PREDICTEDESS

HIGH RELATEDNESS

LOW RELATEDNESS

stingless bees honey

bees

Policing of caste fate

Self determination Social

determination

20% queen production 0.005% queen

production

In the ’70 Bob Trivers showed that In the ’70 Bob Trivers showed that there are also conflict of interests there are also conflict of interests

in the seemingly solid in the seemingly solid parent-parent-offspring bond.offspring bond.

Parent-offspring conflict

Each offspring would like to favour itself over its siblings (r=0.5)

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!

E.g. intra-uterine conflicts

Major transitions in evolution

All the previous also applies at other levels All the previous also applies at other levels

E.g. conflicts between genes within cells E.g. conflicts between genes within cells or or

between cells within multicellular organismsbetween cells within multicellular organisms

“intragenomic conflicts”“intragenomic conflicts”

Intragenomic conflicts

Forms of intragenomic conflict :Forms of intragenomic conflict :

- between genes on homologous chromosomes over - between genes on homologous chromosomes over transmission to gametes (meiotic drive)transmission to gametes (meiotic drive)

- nucleo-cytoplasmic conflicts over optimal sex allocation- nucleo-cytoplasmic conflicts over optimal sex allocation

- conflicts between cells over who ends up producing the - conflicts between cells over who ends up producing the gametesgametes

COOPERATE DRIVE

CO

OP

ER

ATE

DR

IVE

-B0

B -C

Meiotic drive cf. hawk-dove game

But there are differences

GenesOrganisms

Option to breed no usuallyindependently

Fighting strategy poisoning physical aggression

Type of ESS pure mixed

Nucleo-cytoplasmatic conflict

• Nuclear genesNuclear genesrrFF=0.5 , =0.5 , rrMM=0.5=0.5

• Cytoplasmic genes (mitochondria, some Cytoplasmic genes (mitochondria, some bacterial symbionts)bacterial symbionts)rrFF=1, =1, rrMM=0=0

Enhance their own transmission if they manipulate their Enhance their own transmission if they manipulate their host to produce a more female biased sex ratio. Males are host to produce a more female biased sex ratio. Males are a dead end. a dead end.

Male killing

Selective killing of males.Selective killing of males.

Increases the survival of Increases the survival of sisters in the same brood, sisters in the same brood, who carry copies of the who carry copies of the maternal element. maternal element.

Works through kin Works through kin selection, cf. fratricide. selection, cf. fratricide.

E.g. E.g. RicketssiaRicketssia, , WolbachiaWolbachia and and Spiroplasma Spiroplasma in ladybird beetlein ladybird beetle

Cytoplasmic male sterility (CMS)

In approx. 4% of all In approx. 4% of all hermaphrodite plants. hermaphrodite plants.

Mitochondrial gene that Mitochondrial gene that benefits the female benefits the female function by sterilising the function by sterilising the male function.male function.

Nuclear genes are selected Nuclear genes are selected to suppress CMS.to suppress CMS.

Feminisation

Feminisation of genetic Feminisation of genetic males. males.

Presumably works by Presumably works by suppressing the androgenic suppressing the androgenic gland.gland.

Occurs in woodlice Occurs in woodlice ((WolbachiaWolbachia))..

Induction of parthenogenesis

Induction of asexual Induction of asexual reproduction, resulting in reproduction, resulting in an all-female brood. an all-female brood.

Occurs in some parasitoid Occurs in some parasitoid wasps (wasps (WolbachiaWolbachia).).

“Maternal sex-ratio”

Manipulates her host (Manipulates her host (NasoniaNasonia) ) to fertilise more eggs than she is to fertilise more eggs than she is selected to. selected to.

Nasonia Nasonia is haplodiploid, so is haplodiploid, so fertilised eggs develop as fertilised eggs develop as females. females.

Exact nature of “maternal sex Exact nature of “maternal sex ratio” is as yet unknown. ratio” is as yet unknown.

Evolution of multicellularity

Slime molds

Dilemma cf. caste conflict

EACH LARVA WANTS TOBECOME A NEW QUEEN

? SPORE

SOMA CELL

EACH CELL WANTS TO BECOME A

SPORE

?

>1 clone>1 cloneLOW LOW rr

1 clone1 cloneHIGH HIGH rr

DeAngelo DeAngelo et al.et al. 1990 1990

An experiment

Strassmann Strassmann et al.et al. 2001 2001

BB

Green beard genes: ultimate Green beard genes: ultimate selfish genesselfish genes

Bb

Bb

Bb

Bb

Bb

Keller & Ross 1998Keller & Ross 1998Gp-9 allozyme locusGp-9 allozyme locus

The End

the evolution of conflict and cooperation lecture in the population biology and population genetics...

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