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