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Altruism by non-relatives
Reciprocity - incur a cost now in anticipation of receiving a benefit later
Modelling - use Game Theory - John Nash
Altruism by non-relatives
Prisoner’s Dilemma
2 prisoners - caught and jailed for a petty crime
- suspected of having committed a more serious crime
Altruism by non-relatives
Prisoner’s Dilemma
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
Altruism by non-relatives
Prisoner’s Dilemma
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)
Altruism by non-relatives
Prisoner’s Dilemma
T > R > P > S
This relationship of payoffs must hold
Temptation > Reward > Punishment > Sucker’s
Altruism by non-relatives
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
Altruism by non-relatives
Prisoner’s Dilemma
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
Altruism by non-relatives
Prisoner’s Dilemma
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
Altruism by non-relatives
Prisoner’s Dilemma
Benefits of tit-for-tat
1. Initially cooperative
2. Quick to retaliate
3. Quick to forgive
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 - only dominant male mates
Courtship dance
DominantSubordinate
Altruism
Reciprocity- in mate acquisition
Does subordinate male assume role of dominant?
Copulations per hour: previous alpha male
Copulations per hour: New alpha male
predicted
• •
••
••
•
•
observed
Altruism
Reciprocity- in mate acquisition
Why have 2 males?
- females are attracted to 2-male courtship groups
Altruism
Reciprocity- in predator detection
Meerkats - sentinels
-forage in groups - not related
-every so often - one animal standsto look for predators
-sentinel warns of approaching predator
Altruism
Reciprocity- in predator detection
Meerkats - sentinels
This behaviour is adaptive if:
Chance of being preyed on while acting as a sentinel
Survivorship while others are sentinels<
Altruism
Reciprocity- in predator detection
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