Solitary breedingSolitary breeding Colonial breedingColonial breeding Communal breedingCommunal breeding Cooperative breedingCooperative breeding –Helpers at the nest EusocialityEusociality

Altruistic behaviors impart direct costsAltruistic behaviors impart direct costs –Negative effect on actor’s reproductive success … and indirect benefits… and indirect benefits –Positive effect on recipient’s reproductive success The origin and persistence of altruismThe origin and persistence of altruism –How can an altruistic strategy spread in a selfish population? –How can an altruistic strategy resist selfish cheaters?

Models assume genetic basis of variationModels assume genetic basis of variation Genetic variability in stem-ness of slime moldsGenetic variability in stem-ness of slime molds

Status in eusocial insectsStatus in eusocial insects –Nutrition, pheromones, age, and social environment Habitat saturation promotes helping in the Seychelles warblerHabitat saturation promotes helping in the Seychelles warbler Smith et al J Insect Behav 21:

CostsCosts –Present breeding –Future survival, fecundity BenefitsBenefits –Reciprocity –Inheritance Breeding statusBreeding status Learned skillsLearned skills TerritoryTerritory CoalitionsCoalitions PrestigePrestige White- winged chough

CostsCosts –Increased competition Brotherly fights in fig waspsBrotherly fights in fig wasps BenefitsBenefits –Helpers at the nest actually do help Food provisioningFood provisioning Predator protectionPredator protection Reduce work load on breeding pairReduce work load on breeding pair Helpers removed Controls Florida scrub jay

Consider a large, stationary population in which altruism is initially rareConsider a large, stationary population in which altruism is initially rare –ρ = mean encounter rate of altruists –Altruists growth rate = 1 – c + ρ × b –Selfish growth rate = 1 Altruists grow if 1 – c + ρ × b > 1Altruists grow if 1 – c + ρ × b > 1 Rearrange to ρ > c / bRearrange to ρ > c / b Hamilton’s rule states altruistic allele will grow if r > c / bHamilton’s rule states altruistic allele will grow if r > c / b It turns out that r = ρIt turns out that r = ρ

Spatial structure of kinshipSpatial structure of kinship –Altruistic core, variable front Kin competitionKin competition –Solutions Competition does not completely overlap cooperation in time /spaceCompetition does not completely overlap cooperation in time /space Mobility and altruismMobility and altruism –High cost to mobility promotes altruism –Mobile cheaters prosper Ecology of unconditional altruism

High relatedness promotes altruismHigh relatedness promotes altruism Haplo-diploidy in HymenopteraHaplo-diploidy in Hymenoptera –Haploid males –Diploid females If monogamy…If monogamy… –r sisters = 0.75 –r mother-daughter = 0.50 Relatedness decreases with multiple queens, fathersRelatedness decreases with multiple queens, fathers –Constraints, high benefits of altruism maintain sociality

If a big group is good for you, and cooperation helps your group grow, cooperation may be worth the costsIf a big group is good for you, and cooperation helps your group grow, cooperation may be worth the costs Big group advantagesBig group advantages –Foraging –Predator avoidance –Reproduction –Group-level competition Group augmentation

The setupThe setup –One defects Freedom / 10 yrsFreedom / 10 yrs –Both defect 5 yrs each5 yrs each –Neither defects 6 months each6 months each –Solution Always defect!Always defect! Iterated PD’s has other solutions…Iterated PD’s has other solutions…

Advantages of conditional altruismAdvantages of conditional altruism Tit-for-tat (TFT)Tit-for-tat (TFT) Win-Stay-Lose-Shift (WSLS)Win-Stay-Lose-Shift (WSLS) Memory helpsMemory helps –Individual recognition Examples of reciprocal altruism in nature are rareExamples of reciprocal altruism in nature are rare –Continuous donation makes it hard to evolve Conditional altruism: Donor sensitivity

“Nepotism”“Nepotism” –Mechanisms Direct recognition of genetic similarityDirect recognition of genetic similarity FamiliarityFamiliarity Preferentially donate to reputable individualsPreferentially donate to reputable individuals –“Image score” and indirect reciprocity –Requires strong cognitive abilities

The tragedy of the commonsThe tragedy of the commons VolunteeringVolunteering –Participation is optional, costly SpecializationSpecialization –Reproductive skew –Cheaters suffer Social controlSocial control –Breeding suppression –Usurpation stopped by queen & workers –Incentives / concessions to help