Selfish restraint and kin selection Directing selfish behaviors to those who are unrelated Ex: salamander tadpoles in two morphs: typical or cannibalistic Cooperation Behaviors selected that benefit a recipient. Either altruistic ( -,+) or mutualistic (+,+). Can occur across species. For cooperation to persist, free-riding must be eliminated or minimized Prisoner s cooperate Other player defect cooperate Player A defect R 1 year term T no jail time S 4-year term P 2 year term T > R > P > S and R > (S+T) 2 1
Prisoner s cooperate Other player defect cooperate Player A defect R reward for coop T temptation to defect S sucker! P punishment T > R > P > S and R > (S+T) 2 Cooperation is not an ESS, but defection is How can cooperation still be selected for? Kin selection By-product benefits (includes mutualism) Reciprocity Enforcement Several individuals cooperate in rearing young. Helpers incur costs of care to help raise young that is often not theirs. Why take on these costs? Why stay? Why help? Are benefits direct or indirect? Scrub jay Cooperative breeding Dhole Meerkat 2
3% of birds and mammals breed cooperatively Communal groups Cichlids Helpers at the nest Very rare in other vertebrates Long-tailed tits Black-backed jackals Communal groups There is shared parentage of young and all help in raising young. Often one dominant individual produces most of the offspring. Group living gives advantages Ex: meerkats, wolves, jackals, acorn woodpeckers Meerkat: dominant female has 80% of offspring Helpers at the nest Adults forego their own reproduction to help raise their own siblings Ex: red-cockaded woodpeckers, scrub jays, African bee-eaters, pine voles pine voles scrub jays bee-eaters 3
Helpers at the nest Why stay and not go off to reproduce on your own? Long-tailed tits Scrub jays Ok, we know why they stay..what do longtailed tits gain from helping? Helping and kin discrimination by calls Best of a bad situation This helper effect on RS is common Indirect benefits from kin selection 4
By-product mutualism Cooperating for a task is synergistic and more beneficial than free-riding (Prisoner s delight example p.341) Co-founding ant queens cooperate to more quickly excavate and build nest Fight to death once nest is begun By-product mutualism Pied kingfishers have several male helpers: Primary son from earlier nest (kin sel) Secondary unrelated, only feed the female (mutualism) By-product mutualism Meerkat group size and direct benefits Indirect benefits (kin selection) also 5
Reciprocity Olive baboon males will form partnerships A male will join another in fighting an adversary Males help those who have helped them in the past chimp partnership baboons fighting Reciprocity Since reward is delayed for the helping individual, how is free-riding avoided? Thanks errr I ll groom you sometime next week.. Repeated interactions Iterations of the prisoner s dilemma selects for tit for tat strategy (TFT) 6
The best strategies for iterated PD The best strategies were nice - don t be the first to defect Respond when provoked But be forgiving IPD is not a zero-sum game it s ok if your partner gains points, too Best conditions for reciprocity Reliable meetings with indiv s over time, recognition and recall of these meetings Benefit outweighs the cost ( hedging ) But can other mechanisms explain helping? Reciprocity Blood sharing in vampire bats % of pre-fed weight 110 100 90 80 70 cost to donor benefit to recipient 50 40 30 20 10 0 Hours to death from starvation Fig. 12.7 7
All possible Donors and recipients Does reciprocity in animals truly exist? Do vampire bats recognize cheaters? Can helping be explained via other means? Enforcement of cooperation Adding to Prisoner s dilemma Now any advantage to free riding may be outweighed by punishment costs Fairy wren helper removal during breeding vs. non-breeding 8
Enforcement of cooperation Dominant breeders suppress reproduction of subordinates via hormones, aggression dwarf mongoose meerkat females fight for dominance Bee-eater father recruits son to help and not breed Enforcement of cooperation Tamarin females have low levels of estrogen and lutenizing hormone until they leave their family group. tamarins Enforcement of cooperation Eviction in meerkats 9
Cooperation case study Are there indirect and/or direct benefits? Seychelles warbler Habitat saturation influences C (best of bad job?) but r is very low, direct benefits possible 10