Sociality and Social Behaviour (Part 2). Altruism by non-relatives Reciprocity - incur a cost now in anticipation of receiving a benefit later Modelling

Sociality and Social Behaviour(Part 2)

Altruism by non-relatives

Reciprocity - incur a cost now in anticipation of receiving a benefit later

Modelling - use Game Theory - John Nash


Prisoner’s Dilemma

2 prisoners - caught and jailed for a petty crime

- suspected of having committed a more serious crime



Each prisoner (player) has a choice

cooperate - deny all knowledge of the serious crime

defect - accuse the other of the more serious crime

Reward for defecting - forgiven minor crime



Each strategy has a payoff

Payoff depends on behaviour of the opponent

1. Both cooperate - both get a reward - R

2. Both defect - both get punished - P

3. One cooperates & one defects

- defector set free - T (temptation payoff)

- cooperator jailed - S (sucker’s payoff)



T > R > P > S

This relationship of payoffs must hold

Temptation > Reward > Punishment > Sucker’s


Maximum sentence - 12 years (10 for major, 2 for minor)

What are the years saved by each strategy?

Cooperate

Cooperate

Defect

Defect

T = 12

S = 0Player A

Player B

R = 10

P = 2

Plays first



How should they behave?

Player A-should defect - always saves something

-if B cooperates - T > R

-if B defects - P > S

Player B

If both defect do worse than if they cooperate

R > P



How should they behave?

After a number of simulations with more thanone move,

Best strategy is a tit-for-tat

-cooperate on first move and then do what opponent did on previous move



Benefits of tit-for-tat

1. Initially cooperative

2. Quick to retaliate

3. Quick to forgive

Altruism

Does this work in nature?

Kin Selection

Reciprocity

Altruism

Kin Selection

- in mate acquisition

Wild turkeys- male progeny of a single brood- group for life

-dominance hierarchy - only dominant male mates

Altruism

Kin Selection

- in mate acquisition

Reproductive success of non-mating males-realized through RS of brother

How?

If brother mates with four females -non-maters RS = 4 x relatedness x .5 (to account for female’s contribution)

= 4 x 0.5 x 0.5 = 1.0

Altruism

Reciprocity- in mate acquisition

Long tailed manakins

Altruism


Long tailed manakins - only dominant male mates

Courtship dance

DominantSubordinate

Altruism


Does subordinate male assume role of dominant?

Copulations per hour: previous alpha male

Copulations per hour: New alpha male

predicted

• •

••

••

•

•

observed

Altruism


Why have 2 males?

- females are attracted to 2-male courtship groups

Altruism

Reciprocity- in predator detection

Meerkats - sentinels

Altruism



-forage in groups - not related

-every so often - one animal standsto look for predators

-sentinel warns of approaching predator

Altruism



This behaviour is adaptive if:

Chance of being preyed on while acting as a sentinel

Survivorship while others are sentinels<

Altruism


But is this really reciprocity?

Alternative hypothesis (selfish):

“Sentinels” are really just animals who have finished feeding and are looking for predators to protect themselves.

Altruism

But is this really reciprocity?

Some predictions from reciprocity hypothesis:

Prediction Observation

Regular rotation of sentinel duty

Sentinel duty appears to be haphazard

Sentinel duty has risk of succumbing to predator

Sentinels are usually closer to an escape burrow

No difference in sentinel time when solitary

Less time is spent in predator detection in groups

Documents

Sociality and Social Behaviour (Part 2). Altruism by non-relatives Reciprocity - incur a cost now in anticipation of receiving a benefit later Modelling