COOPERATION Tit-for-Tat and reciprocal altruism By-product mutualism We’ll save for later: Kin Selection Coop in Humans

General payoff for costly Two roads to Cooperation Coop Defect TFT Defect Coop (b-c) -c TFT (b-c) (-c) Defect b General payoff for costly Cooperation Defect (b) Prisoner's Dilemma: the only ESS is to Defect TFT is an ESS when: (-)  c b > Reciprocal altruism OR Cooperation is an ESS when: r > c/b where r = coefficient of relatedness (Kin Selection)

Reciprocity – Food sharing in Vampire Bats (Gerald Wilkinson) Evidence for repeated interactions – unrelated group members may share a roost for several years

Data from natural roosts 1) Bats tend not to be related to each other 2) Cooperation occurs among commonly associating bats Associations Cooperating Pairs Associations All Pairs

Benefit of receiving aid outweighs the cost of donating cost of giving up 5% of your fed weight weight benefit of receiving that 5% starvation time since last meal (hrs)

Benefit of receiving aid outweighs the cost of donating cost of giving up 5% of your fed weight weight benefit of receiving that 5% starvation cost benefit time since last meal (hrs)

Using experimental roosts Wilkinson showed: -- 12 of 13 regurgitations were between members of the same roost in the field -- Recipients reciprocated to previous donors more than was expected by chance probability of future interaction is high individuals can recognize each other the benefit of a cooperative act greatly outweighs the cost potential for future retaliation is one does not cooperate

Switching gender roles as reciprocal altruism Egg trading and reciprocity in sequentially hermaphroditic fishes, e.g., black hamlet fish Switching gender roles as reciprocal altruism

Are these guppies cooperating? Predator-inspection behavior in guppies

Is c > a ? Payoff matrix in terms of the probability of not being eaten by the predator Is c > a ? Cooperate (inspect) Defect a b c d Yes, inspection is costly

Information is Public This individual reacts similarly as the lcose individual when the latter is visible

Milinski’s experiments with mirrors and sticklebacks shows retaliation Mirror projects a fellow inspector traveling side by side the length of the aquarium Mirror projected 32° shows fellow inspector dropping back and finally disappearing the closer the focal fish approaches the predator

Reciprocal Altruism and predator mobbing

(1) Defector Cooperator (2)

Byproduct mutualism Problems with Tit-for-Tat Tracking debts owed and favors given requires complex score-keeping Cooperate Defect 5 1 Cooperate is the sole ESS

Prisoner’s Dilemma and byproduct mutualism in blue jays Trained blue jays choose a perch that delivers: Large rewards to its neighbor Or (2) Small rewards to itself

Prisoner’s Dilemma Byproduct Mutualism Prisoner’s Dilemma Mutual cooperation Mutual defection One coop, one defect ????? Why don’t they coop Here ???? Individuals act in concert with the theory (in part) Individuals learn quickly to respond accordingly Individuals do not cooperate in the Prisoner’s Dilemma even when iterated Why the mutual defection even when the PD game is iterated between jays?

It is only through iterated cooperation that both jays can receive their largest payoff Individual play of the game has a large temptation to cheat – Prisoner’s Dilemma

The structure of the Payoff Matrix Matters – organisms learn/have knowledge of the payoffs and respond accordingly (Pris Dil vs. Byproduct Mut) Reciprocal Altruism (TFT) is broadly distributed in the animal world Its seen in simple organisms (fish) largely and social spp (humans later) Sex, social foraging, predator avoidance/mobbing, and others for sure

The trick is for jays to see their food accumulating in transparent containers and every 4 turns they get to feed. Proportion cooperating Opponent’s strategy TFT Accumulating benefits (low discount) Unaccumulating (high discount)