• Solitary breedingSolitary breeding• Colonial breedingColonial breeding• Communal Communal

breedingbreeding• Cooperative Cooperative

breedingbreeding– Helpers at the nestHelpers at the nest

• EusocialityEusociality

• Altruistic behaviors impart direct costsAltruistic behaviors impart direct costs– Negative effect on actor’s reproductive Negative effect on actor’s reproductive

success success

• … … and indirect benefitsand indirect benefits– Positive effect on recipient’s reproductive Positive effect on recipient’s reproductive

successsuccess

• The origin and persistence of altruismThe origin and persistence of altruism– How can an altruistic strategy spread in a How can an altruistic strategy spread in a

selfish population?selfish population?– How can an altruistic strategy resist selfish How can an altruistic strategy resist selfish

cheaters?cheaters?

• Models Models assume assume genetic basis genetic basis of variationof variation

• Genetic Genetic variability in variability in stem-ness of stem-ness of slime moldsslime molds

• Status in eusocial insectsStatus in eusocial insects– Nutrition, pheromones, age, and Nutrition, pheromones, age, and

social environmentsocial environment

• Habitat saturation promotes Habitat saturation promotes helping in the Seychelles helping in the Seychelles warblerwarbler

Smith et al. 2008 J Insect Behav 21:394-406Smith et al. 2008 J Insect Behav 21:394-406

• CostsCosts– Present breedingPresent breeding– Future survival, Future survival,

fecundityfecundity

• BenefitsBenefits– ReciprocityReciprocity– InheritanceInheritance

• Breeding statusBreeding status• Learned skillsLearned skills• TerritoryTerritory• CoalitionsCoalitions• PrestigePrestige

White-winged chough

• CostsCosts– Increased Increased

competitioncompetition• Brotherly fights in fig Brotherly fights in fig

waspswasps

• BenefitsBenefits– Helpers at the nest Helpers at the nest

actually do helpactually do help• Food provisioningFood provisioning• Predator protectionPredator protection• Reduce work load on Reduce work load on

breeding pairbreeding pair

Helpers removed

Controls

Florida Florida scrub jayscrub jay

• Consider a large, stationary population in Consider a large, stationary population in which altruism is initially rarewhich altruism is initially rare– ρρ = mean encounter rate of altruists = mean encounter rate of altruists– Altruists growth rate = Altruists growth rate = 11 – c + – c + ρρ × b × b– Selfish growth rate = Selfish growth rate = 11

• Altruists grow if Altruists grow if 11 – c + – c + ρρ × b > × b > 11• Rearrange to Rearrange to ρρ > c / b > c / b• Hamilton’s rule states altruistic allele will Hamilton’s rule states altruistic allele will

grow if grow if rr > > c / bc / b• It turns out that It turns out that r = r = ρρ

• Spatial structure of Spatial structure of kinshipkinship– Altruistic core, variable Altruistic core, variable

frontfront

• Kin competitionKin competition– SolutionsSolutions

• Competition does not Competition does not completely overlap completely overlap cooperation in time /spacecooperation in time /space

• Mobility and altruismMobility and altruism– High cost to mobility High cost to mobility

promotes altruismpromotes altruism– Mobile cheaters prosperMobile cheaters prosper

Ecology of unconditional Ecology of unconditional altruismaltruism

• High relatedness promotes High relatedness promotes altruismaltruism

• Haplo-diploidy in Haplo-diploidy in HymenopteraHymenoptera– Haploid malesHaploid males– Diploid femalesDiploid females

• If monogamy…If monogamy…– r r sisters sisters = 0.75= 0.75– r r mother-daughtermother-daughter = 0.50 = 0.50

• Relatedness decreases with Relatedness decreases with multiple queens, fathersmultiple queens, fathers– Constraints, high benefits of Constraints, high benefits of

altruism maintain socialityaltruism maintain sociality

• If a big group is If a big group is good for you, and good for you, and cooperation helps cooperation helps your group grow, your group grow, cooperation may cooperation may be worth the costsbe worth the costs

• Big group Big group advantagesadvantages– ForagingForaging– Predator avoidancePredator avoidance– ReproductionReproduction– Group-level Group-level

competitioncompetition

Group augmentationGroup augmentation

• The setupThe setup– One defectsOne defects• Freedom / 10 yrsFreedom / 10 yrs

– Both defectBoth defect• 5 yrs each5 yrs each

– Neither defectsNeither defects• 6 months each6 months each

– SolutionSolution• Always defect!Always defect!

• Iterated PD’s has other Iterated PD’s has other solutions…solutions…

• Advantages of Advantages of conditional altruismconditional altruism

• Tit-for-tat (TFT)Tit-for-tat (TFT)• Win-Stay-Lose-Shift Win-Stay-Lose-Shift

(WSLS)(WSLS)• Memory helpsMemory helps– Individual recognitionIndividual recognition

• Examples of reciprocal Examples of reciprocal altruism in nature are altruism in nature are rarerare– Continuous donation Continuous donation

makes it hard to evolvemakes it hard to evolve

Conditional altruism: Conditional altruism: Donor sensitivityDonor sensitivity

• ““Nepotism”Nepotism”– MechanismsMechanisms• Direct recognition of Direct recognition of

genetic similaritygenetic similarity• FamiliarityFamiliarity

• Preferentially donate to Preferentially donate to reputable individualsreputable individuals– ““Image score” and Image score” and

indirect reciprocityindirect reciprocity– Requires strong Requires strong

cognitive abilitiescognitive abilities

• The tragedy of the commonsThe tragedy of the commons• VolunteeringVolunteering– Participation is optional, costlyParticipation is optional, costly

• SpecializationSpecialization– Reproductive skewReproductive skew– Cheaters sufferCheaters suffer

• Social controlSocial control– Breeding suppressionBreeding suppression– Usurpation stopped by queen Usurpation stopped by queen & & workersworkers– Incentives / concessions to helpIncentives / concessions to help