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

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 Defect T = 12 S = 0 Player 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 than one 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 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 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

Altruism Reciprocity - in predator detection Meerkats - sentinels -forage in groups - not related -every so often - one animal stands to 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: PredictionObservation 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