1. Types of Social Interactions Cooperation = mutualism Cooperation = mutualism – Fitness gains for both participants Altruism Altruism – Fitness gain for recipient – Cost for actor Selfishness Selfishness – Actor gains – Recipient loses Spite Spite – Fitness loss for both participants Cooperation = mutualism Cooperation = mutualism – Fitness gains for both participants Altruism Altruism – Fitness gain for recipient – Cost for actor Selfishness Selfishness – Actor gains – Recipient loses Spite Spite – Fitness loss for both participants

3. Prevalence of Altruism Appears to be common in nature Appears to be common in nature – Young macaws help parents raise their siblings instead of reproducing themselves – Human runs into a burning house to save a child Darwin mentioned that altruism was a “special difficulty” for his theory Darwin mentioned that altruism was a “special difficulty” for his theory How can an allele that codes for altruism survive in the face of natural selection? How can an allele that codes for altruism survive in the face of natural selection? Appears to be common in nature Appears to be common in nature – Young macaws help parents raise their siblings instead of reproducing themselves – Human runs into a burning house to save a child Darwin mentioned that altruism was a “special difficulty” for his theory Darwin mentioned that altruism was a “special difficulty” for his theory How can an allele that codes for altruism survive in the face of natural selection? How can an allele that codes for altruism survive in the face of natural selection?

4. Kin Selection and the Evolution of Altruism William Hamilton developed a genetic model showing how an allele for altruistic behavior could persist William Hamilton developed a genetic model showing how an allele for altruistic behavior could persist Coefficient of relationship, r Coefficient of relationship, r – Probability that homozygous alleles in two individuals are identical by descent Hamilton’s Rule Hamilton’s Rule – Altruistic behavior will spread if Br – C > 0 Br – C > 0 – B = benefit to recipient – C = cost to actor William Hamilton developed a genetic model showing how an allele for altruistic behavior could persist William Hamilton developed a genetic model showing how an allele for altruistic behavior could persist Coefficient of relationship, r Coefficient of relationship, r – Probability that homozygous alleles in two individuals are identical by descent Hamilton’s Rule Hamilton’s Rule – Altruistic behavior will spread if Br – C > 0 Br – C > 0 – B = benefit to recipient – C = cost to actor

5. Kin Selection and the Evolution of Altruism Altruism will spread when benefits to recipient are great, cost to actor is small, and participants are closely related Altruism will spread when benefits to recipient are great, cost to actor is small, and participants are closely related Inclusive Fitness Inclusive Fitness – Direct fitness results from personal reproduction – Indirect fitness results from reproduction by relatives Altruism will spread when benefits to recipient are great, cost to actor is small, and participants are closely related Altruism will spread when benefits to recipient are great, cost to actor is small, and participants are closely related Inclusive Fitness Inclusive Fitness – Direct fitness results from personal reproduction – Indirect fitness results from reproduction by relatives

6. Kin Selection and the Evolution of Altruism Indirect fitness accrues when relatives reproduce more than they would have without aid by actor Indirect fitness accrues when relatives reproduce more than they would have without aid by actor When natural selection favors the spread of alleles that increase indirect fitness, Kin Selection occurs When natural selection favors the spread of alleles that increase indirect fitness, Kin Selection occurs Kin selection explains many cases of apparent altruism Kin selection explains many cases of apparent altruism – True altruism does not exist in nature Indirect fitness accrues when relatives reproduce more than they would have without aid by actor Indirect fitness accrues when relatives reproduce more than they would have without aid by actor When natural selection favors the spread of alleles that increase indirect fitness, Kin Selection occurs When natural selection favors the spread of alleles that increase indirect fitness, Kin Selection occurs Kin selection explains many cases of apparent altruism Kin selection explains many cases of apparent altruism – True altruism does not exist in nature

7. Calculating Coefficients of Relatedness Haldane was quoted in a bar: “I would lay down my life for the sake of two brothers or eight cousins” Haldane was quoted in a bar: “I would lay down my life for the sake of two brothers or eight cousins” Perform path analysis to assess relatedness Perform path analysis to assess relatedness – Parents related to offspring 1/2 – Full siblings related 1/2 – Half siblings related 1/4 – Cousins related 1/8 Haldane was quoted in a bar: “I would lay down my life for the sake of two brothers or eight cousins” Haldane was quoted in a bar: “I would lay down my life for the sake of two brothers or eight cousins” Perform path analysis to assess relatedness Perform path analysis to assess relatedness – Parents related to offspring 1/2 – Full siblings related 1/2 – Half siblings related 1/4 – Cousins related 1/8

9. Alarm Calling in Belding’s Ground Squirrels Females are more likely to give alarm calls than males Females are more likely to give alarm calls than males Mothers, daughters, and sisters were more likely to assist each other chasing trespassers off their territories than unrelated individuals Mothers, daughters, and sisters were more likely to assist each other chasing trespassers off their territories than unrelated individuals Females are more likely to give alarm calls than males Females are more likely to give alarm calls than males Mothers, daughters, and sisters were more likely to assist each other chasing trespassers off their territories than unrelated individuals Mothers, daughters, and sisters were more likely to assist each other chasing trespassers off their territories than unrelated individuals

11. White-Fronted Bee Eaters Young adults forgo breeding to help their parents raise their siblings Young adults forgo breeding to help their parents raise their siblings – Nest building, nest defense, food delivery, incubation Helping at the nest usually found in species where breeding opportunities are limited Helping at the nest usually found in species where breeding opportunities are limited – Best of a bad job strategy Bee eater coefficient of relatedness determines if they will help Bee eater coefficient of relatedness determines if they will help Young adults forgo breeding to help their parents raise their siblings Young adults forgo breeding to help their parents raise their siblings – Nest building, nest defense, food delivery, incubation Helping at the nest usually found in species where breeding opportunities are limited Helping at the nest usually found in species where breeding opportunities are limited – Best of a bad job strategy Bee eater coefficient of relatedness determines if they will help Bee eater coefficient of relatedness determines if they will help

12. White-Fronted Bee Eaters

13. Presence of helpers increases parental success by 0.47 fledglings Presence of helpers increases parental success by 0.47 fledglings

14. Evolution of Eusociality True sociality describes social systems with three characteristics True sociality describes social systems with three characteristics – Overlap in generations – Cooperative brood care – Specialized castes of nonreproductive individuals Will examine two groups Will examine two groups – Hymenoptera – Naked mole rats True sociality describes social systems with three characteristics True sociality describes social systems with three characteristics – Overlap in generations – Cooperative brood care – Specialized castes of nonreproductive individuals Will examine two groups Will examine two groups – Hymenoptera – Naked mole rats

16. Haplodiploidy and Eusocial Hymenoptera Hymenopterans exhibit most extreme form of eusociality Hymenopterans exhibit most extreme form of eusociality Millions of individuals per colony Millions of individuals per colony – Very few reproduce How can this persist? How can this persist? Hamilton proposed that haplodiploidy may be the reason Hamilton proposed that haplodiploidy may be the reason – Females grow from fertilized eggs – Males grow from unfertilized eggs Hymenopterans exhibit most extreme form of eusociality Hymenopterans exhibit most extreme form of eusociality Millions of individuals per colony Millions of individuals per colony – Very few reproduce How can this persist? How can this persist? Hamilton proposed that haplodiploidy may be the reason Hamilton proposed that haplodiploidy may be the reason – Females grow from fertilized eggs – Males grow from unfertilized eggs

17. Haplodiploidy and Eusocial Hymenoptera Because of disparity in chromosome number, sisters share 75% of genes Because of disparity in chromosome number, sisters share 75% of genes – Parents and offspring share 50% – Females are better off rearing sisters than offspring Testing haplodiploidy hypothesis Testing haplodiploidy hypothesis – Workers should prefer to invest in sisters over brothers Related to sisters 3/4 Related to sisters 3/4 Related to brothers 1/4 Related to brothers 1/4 Because of disparity in chromosome number, sisters share 75% of genes Because of disparity in chromosome number, sisters share 75% of genes – Parents and offspring share 50% – Females are better off rearing sisters than offspring Testing haplodiploidy hypothesis Testing haplodiploidy hypothesis – Workers should prefer to invest in sisters over brothers Related to sisters 3/4 Related to sisters 3/4 Related to brothers 1/4 Related to brothers 1/4

19. Haplodiploidy and Eusocial Hymenoptera Testing haplodiploidy hypothesis Testing haplodiploidy hypothesis – Workers should favor 3:1 sex ratio – Queens are equally related to sons and daughters and should favor 1:1 sex ratio – Conflict of interest between queens and workers – Sudstrom found that wood ant queens lays equal numbers of male and female eggs – Workers selectively killed male eggs prior to hatching – Workers win sex ratio battle Testing haplodiploidy hypothesis Testing haplodiploidy hypothesis – Workers should favor 3:1 sex ratio – Queens are equally related to sons and daughters and should favor 1:1 sex ratio – Conflict of interest between queens and workers – Sudstrom found that wood ant queens lays equal numbers of male and female eggs – Workers selectively killed male eggs prior to hatching – Workers win sex ratio battle

20. Haplodiploidy and Eusocial Hymenoptera Does haplodiploidy explain eusociality? Does haplodiploidy explain eusociality? – Workers should favor production of sisters if all have the same father Honeybee queens mate over 17 times when founding a colony Honeybee queens mate over 17 times when founding a colony Average r for workers is 1/3 Average r for workers is 1/3 In this case, workers are not more closely related to sisters than offspring In this case, workers are not more closely related to sisters than offspring Sometimes more than one queen founds nest Sometimes more than one queen founds nest Some workers may not be related at all Some workers may not be related at all Many eusocial species are not haplodiploid Many eusocial species are not haplodiploid Does haplodiploidy explain eusociality? Does haplodiploidy explain eusociality? – Workers should favor production of sisters if all have the same father Honeybee queens mate over 17 times when founding a colony Honeybee queens mate over 17 times when founding a colony Average r for workers is 1/3 Average r for workers is 1/3 In this case, workers are not more closely related to sisters than offspring In this case, workers are not more closely related to sisters than offspring Sometimes more than one queen founds nest Sometimes more than one queen founds nest Some workers may not be related at all Some workers may not be related at all Many eusocial species are not haplodiploid Many eusocial species are not haplodiploid

21. Using Phylogenies to Analyze Social Evolution Hunt reconstructed a phylogeny of hymenopterans Hunt reconstructed a phylogeny of hymenopterans – All are haplodiploid – Few families are eusocial – Eusocial families not closely related – Eusociality must have evolved multiple times – Evolved in groups that build complex nests and have extended care for larvae Hunt reconstructed a phylogeny of hymenopterans Hunt reconstructed a phylogeny of hymenopterans – All are haplodiploid – Few families are eusocial – Eusocial families not closely related – Eusociality must have evolved multiple times – Evolved in groups that build complex nests and have extended care for larvae

23. Using Phylogenies to Analyze Social Evolution Phylogeny suggests that the primary agent favoring eusociality is not genetic Phylogeny suggests that the primary agent favoring eusociality is not genetic Best of a bad job hypothesis Best of a bad job hypothesis – Building a complex nest and caring for many larvae would be impossible for a female to do by herself – Must examine factors that affect B and C as well as r Phylogeny suggests that the primary agent favoring eusociality is not genetic Phylogeny suggests that the primary agent favoring eusociality is not genetic Best of a bad job hypothesis Best of a bad job hypothesis – Building a complex nest and caring for many larvae would be impossible for a female to do by herself – Must examine factors that affect B and C as well as r

24. Facultative Strategies in Paper Wasps Polistes paper wasps are not completely eusocial Polistes paper wasps are not completely eusocial Workers are not sterile Workers are not sterile Females may reproduce on their own Females may reproduce on their own Females pursue one of three strategies Females pursue one of three strategies – Initiate own nest – Join a nest as a helper – Wait for a breeding opportunity Polistes paper wasps are not completely eusocial Polistes paper wasps are not completely eusocial Workers are not sterile Workers are not sterile Females may reproduce on their own Females may reproduce on their own Females pursue one of three strategies Females pursue one of three strategies – Initiate own nest – Join a nest as a helper – Wait for a breeding opportunity

25. Facultative Strategies in Paper Wasps Examine costs and benefits of each strategy Examine costs and benefits of each strategy Nests founded by single females or multifemale groups Nests founded by single females or multifemale groups – Single foundress nests less successful – Multifoundress nests more likely to be rebuilt if destroyed – Fights among foundresses determined by body size – Multifoundress nests grew fastest if large size difference of dominant female and subordinate helpers Examine costs and benefits of each strategy Examine costs and benefits of each strategy Nests founded by single females or multifemale groups Nests founded by single females or multifemale groups – Single foundress nests less successful – Multifoundress nests more likely to be rebuilt if destroyed – Fights among foundresses determined by body size – Multifoundress nests grew fastest if large size difference of dominant female and subordinate helpers

27. Facultative Strategies in Paper Wasps Why would females join a coalition and help rear offspring that are not theirs? Why would females join a coalition and help rear offspring that are not theirs? – Indirect fitness gains because usually related to foundress – Direct fitness gains if foundress dies and a subordinate inherits the nest – Costs and benefits of this strategy depend on female’s body size and coefficient of relatedness Why would females join a coalition and help rear offspring that are not theirs? Why would females join a coalition and help rear offspring that are not theirs? – Indirect fitness gains because usually related to foundress – Direct fitness gains if foundress dies and a subordinate inherits the nest – Costs and benefits of this strategy depend on female’s body size and coefficient of relatedness

28. Facultative Strategies in Paper Wasps If females do not help found nests and wait, they may be able to adopt an already-constructed nest If females do not help found nests and wait, they may be able to adopt an already-constructed nest – Sit-and-wait tactic – They leave their nest in spring and enter a dormant state until the following season to try to take over a new nest If females do not help found nests and wait, they may be able to adopt an already-constructed nest If females do not help found nests and wait, they may be able to adopt an already-constructed nest – Sit-and-wait tactic – They leave their nest in spring and enter a dormant state until the following season to try to take over a new nest

29. Facultative Strategies in Paper Wasps Sociality is facultative in Polistes Sociality is facultative in Polistes Adaptive response to environmental conditions Adaptive response to environmental conditions Important conditions are female body size relative to competitors, coefficient of relatedness, and availability of nest sites Important conditions are female body size relative to competitors, coefficient of relatedness, and availability of nest sites Genetic, social, and ecological factors important Genetic, social, and ecological factors important Sociality is facultative in Polistes Sociality is facultative in Polistes Adaptive response to environmental conditions Adaptive response to environmental conditions Important conditions are female body size relative to competitors, coefficient of relatedness, and availability of nest sites Important conditions are female body size relative to competitors, coefficient of relatedness, and availability of nest sites Genetic, social, and ecological factors important Genetic, social, and ecological factors important

30. Naked Mole Rats Live underground in huge nests in Africa Live underground in huge nests in Africa Colonies of 70-80 members Colonies of 70-80 members Hairless, ectothermic, digest cellulose Hairless, ectothermic, digest cellulose All species are eusocial All species are eusocial – Single queen – 2-3 reproductive males – Workers are males and females Castes change with age Castes change with age – First they tend young – Later they excavate tunnels – The oldest defend the nest Live underground in huge nests in Africa Live underground in huge nests in Africa Colonies of 70-80 members Colonies of 70-80 members Hairless, ectothermic, digest cellulose Hairless, ectothermic, digest cellulose All species are eusocial All species are eusocial – Single queen – 2-3 reproductive males – Workers are males and females Castes change with age Castes change with age – First they tend young – Later they excavate tunnels – The oldest defend the nest

32. Naked Mole Rats Not haplodiploid Not haplodiploid Why are they eusocial? Why are they eusocial? – Highly inbred Average r for siblings is 0.81 Average r for siblings is 0.81 Highest coefficient of relatedness ever recorded in mammals Highest coefficient of relatedness ever recorded in mammals – Still conflict among group members Workers more closely related to offspring than half-siblings Workers more closely related to offspring than half-siblings Not haplodiploid Not haplodiploid Why are they eusocial? Why are they eusocial? – Highly inbred Average r for siblings is 0.81 Average r for siblings is 0.81 Highest coefficient of relatedness ever recorded in mammals Highest coefficient of relatedness ever recorded in mammals – Still conflict among group members Workers more closely related to offspring than half-siblings Workers more closely related to offspring than half-siblings

33. Naked Mole Rats Conflict among group members Conflict among group members – Queens maintain control by physical dominance – If the workers slow their work pace the queen shoves them with her head – Afterwards the workers increase their work pace – Shoves are directed more often towards more distant relatives – Queen maintains eusociality by intimidation Conflict among group members Conflict among group members – Queens maintain control by physical dominance – If the workers slow their work pace the queen shoves them with her head – Afterwards the workers increase their work pace – Shoves are directed more often towards more distant relatives – Queen maintains eusociality by intimidation

35. Parent-Offspring Conflict Parental care is a special case of kin selection Parental care is a special case of kin selection Even parents and offspring can have conflicts in costs and benefits Even parents and offspring can have conflicts in costs and benefits Weaning Conflict Weaning Conflict – Mothers begin to ignore or push young away near end of weaning period – Offspring will scream or attack mother – Fitness interests are not symmetrical Parental care is a special case of kin selection Parental care is a special case of kin selection Even parents and offspring can have conflicts in costs and benefits Even parents and offspring can have conflicts in costs and benefits Weaning Conflict Weaning Conflict – Mothers begin to ignore or push young away near end of weaning period – Offspring will scream or attack mother – Fitness interests are not symmetrical

36. Parent-Offspring Conflict Weaning Conflict Weaning Conflict – Offspring are related to themselves r = 1 – Parents are related to offspring r = 0.5 – Parents are equally related to all offspring and should optimize their investment in each – Offspring demand unequal amount of parental investment Weaning Conflict Weaning Conflict – Offspring are related to themselves r = 1 – Parents are related to offspring r = 0.5 – Parents are equally related to all offspring and should optimize their investment in each – Offspring demand unequal amount of parental investment

37. Parent-Offspring Conflict Weaning Conflict Weaning Conflict – At start of nursing benefit of offspring relative to cost of parent – Ratio declines with time – Young demand more milk which increases parental cost – Young can start finding own food which decreases benefit – Mothers should stop producing milk when benefit to cost ratio reaches 1 Weaning Conflict Weaning Conflict – At start of nursing benefit of offspring relative to cost of parent – Ratio declines with time – Young demand more milk which increases parental cost – Young can start finding own food which decreases benefit – Mothers should stop producing milk when benefit to cost ratio reaches 1

38. Parent-Offspring Conflict Weaning Conflict Weaning Conflict – By continuing to nurse, offspring devalue mother’s cost of care – Offspring should continue to try to nurse until benefit-cost ratio is 1/2 – Period between these stages is weaning conflict – Avoidance and aggressive behavior throughout this period – If half-siblings are produced then ratio should be extended to 1/4 Weaning Conflict Weaning Conflict – By continuing to nurse, offspring devalue mother’s cost of care – Offspring should continue to try to nurse until benefit-cost ratio is 1/2 – Period between these stages is weaning conflict – Avoidance and aggressive behavior throughout this period – If half-siblings are produced then ratio should be extended to 1/4

40. Parent-Offspring Conflict White-fronted Bee Eaters White-fronted Bee Eaters – Sons may set up territory or may help at their parental nest – Fathers coerce sons into helping by harassing sons as they attempt to set up territories Fathers prevent courtship feeding Fathers prevent courtship feeding Harassment is preferentially directed at sons to prevent them from breeding and coerce them to help at the nest Harassment is preferentially directed at sons to prevent them from breeding and coerce them to help at the nest White-fronted Bee Eaters White-fronted Bee Eaters – Sons may set up territory or may help at their parental nest – Fathers coerce sons into helping by harassing sons as they attempt to set up territories Fathers prevent courtship feeding Fathers prevent courtship feeding Harassment is preferentially directed at sons to prevent them from breeding and coerce them to help at the nest Harassment is preferentially directed at sons to prevent them from breeding and coerce them to help at the nest

41. Parent-Offspring Conflict White-fronted Bee Eaters White-fronted Bee Eaters – 16 of 47 observed harassment events resulted in successful recruitment to help – Why don’t sons resist more effectively? Sons are equally related to siblings and own offspring Sons are equally related to siblings and own offspring Parents are more closely related to each offspring than to grandchildren Parents are more closely related to each offspring than to grandchildren Helpers add 0.47 offspring to parental success Helpers add 0.47 offspring to parental success Nearly same as own offspring Nearly same as own offspring – Worth it to save harassment from father White-fronted Bee Eaters White-fronted Bee Eaters – 16 of 47 observed harassment events resulted in successful recruitment to help – Why don’t sons resist more effectively? Sons are equally related to siblings and own offspring Sons are equally related to siblings and own offspring Parents are more closely related to each offspring than to grandchildren Parents are more closely related to each offspring than to grandchildren Helpers add 0.47 offspring to parental success Helpers add 0.47 offspring to parental success Nearly same as own offspring Nearly same as own offspring – Worth it to save harassment from father

42. Parent-Offspring Conflict Siblicide Siblicide – In birds and mammals it is common to kill siblings – Seems maladaptive since r = 1/2 – Lougheed and Anderson studied boobies in Galápagos Islands – Lay clutch of two eggs separated by 2-10 days – First chick often pushes younger from nest Siblicide Siblicide – In birds and mammals it is common to kill siblings – Seems maladaptive since r = 1/2 – Lougheed and Anderson studied boobies in Galápagos Islands – Lay clutch of two eggs separated by 2-10 days – First chick often pushes younger from nest

44. Parent-Offspring Conflict Siblicide Siblicide – Masked boobies push second egg from nest immediately – Blue-footed booby older chicks may reduce food intake during short food shortages to provide extra for sibling During long food shortages they kill their siblings During long food shortages they kill their siblings – What role do parents play? Parents should intervene to prevent death of any of their chicks Parents should intervene to prevent death of any of their chicks Siblicide Siblicide – Masked boobies push second egg from nest immediately – Blue-footed booby older chicks may reduce food intake during short food shortages to provide extra for sibling During long food shortages they kill their siblings During long food shortages they kill their siblings – What role do parents play? Parents should intervene to prevent death of any of their chicks Parents should intervene to prevent death of any of their chicks

45. Parent-Offspring Conflict Siblicide Siblicide – Reciprocal transplant experiment – Chicks more likely to die with masked booby nestmate – Chicks more likely to die with masked booby parents (surrogate or real) – Blue-footed booby parents intervene but masked do not – Why there is a difference among species is not known Siblicide Siblicide – Reciprocal transplant experiment – Chicks more likely to die with masked booby nestmate – Chicks more likely to die with masked booby parents (surrogate or real) – Blue-footed booby parents intervene but masked do not – Why there is a difference among species is not known

47. Reciprocal Altruism What about cooperation among unrelated individuals? What about cooperation among unrelated individuals? Trivers proposed individuals will act altruistically if favor is later returned Trivers proposed individuals will act altruistically if favor is later returned Two conditions for reciprocal alturism to evolve: Two conditions for reciprocal alturism to evolve: – Cost to actor must be smaller than or equal to benefit to recipient – Individuals that fail to reciprocate must be punished What about cooperation among unrelated individuals? What about cooperation among unrelated individuals? Trivers proposed individuals will act altruistically if favor is later returned Trivers proposed individuals will act altruistically if favor is later returned Two conditions for reciprocal alturism to evolve: Two conditions for reciprocal alturism to evolve: – Cost to actor must be smaller than or equal to benefit to recipient – Individuals that fail to reciprocate must be punished

48. Reciprocal Altruism Most likely to evolve when: Most likely to evolve when: – Each individual repeatedly interacts with same set of individuals – Many opportunities for altruism in an individual’s lifetime – Individuals have good memories – Potential altruists interact in symmetrical situations Roughly equal benefits and costs Roughly equal benefits and costs Most likely to evolve when: Most likely to evolve when: – Each individual repeatedly interacts with same set of individuals – Many opportunities for altruism in an individual’s lifetime – Individuals have good memories – Potential altruists interact in symmetrical situations Roughly equal benefits and costs Roughly equal benefits and costs

49. Reciprocal Altruism Will evolve in long-lived, intelligent, social species with small group size, low dispersal rates, and mutual dependence in activities Will evolve in long-lived, intelligent, social species with small group size, low dispersal rates, and mutual dependence in activities Less likely to evolve in species with dominance hierarchies Less likely to evolve in species with dominance hierarchies Difficult to observe and quantify in nature Difficult to observe and quantify in nature Will evolve in long-lived, intelligent, social species with small group size, low dispersal rates, and mutual dependence in activities Will evolve in long-lived, intelligent, social species with small group size, low dispersal rates, and mutual dependence in activities Less likely to evolve in species with dominance hierarchies Less likely to evolve in species with dominance hierarchies Difficult to observe and quantify in nature Difficult to observe and quantify in nature

50. Reciprocal Altruism Blood-Sharing in Vampire Bats Blood-Sharing in Vampire Bats – Social group of 8-12 females and their dependent offspring – Roost together and associate with each other daily – Average r between individuals in study group in Costa Rica was 0.11 – Vampire bats share blood meals – Hunting is difficult and individuals are only successful 67-93% of time Prey are wary Prey are wary Blood-Sharing in Vampire Bats Blood-Sharing in Vampire Bats – Social group of 8-12 females and their dependent offspring – Roost together and associate with each other daily – Average r between individuals in study group in Costa Rica was 0.11 – Vampire bats share blood meals – Hunting is difficult and individuals are only successful 67-93% of time Prey are wary Prey are wary

52. Reciprocal Altruism Blood-Sharing in Vampire Bats Blood-Sharing in Vampire Bats – Without eating for three nights, a bat will starve to death – Both degree of relatedness and degree of association were significantly related to probability of regurgitating blood – Blood-sharing is not random but based on relatedness and hope of future reciprocity Blood-Sharing in Vampire Bats Blood-Sharing in Vampire Bats – Without eating for three nights, a bat will starve to death – Both degree of relatedness and degree of association were significantly related to probability of regurgitating blood – Blood-sharing is not random but based on relatedness and hope of future reciprocity

54. Reciprocal Altruism Territory Defense in Lions Territory Defense in Lions – Females cooperate in defending young against infanticidal males, hunting prey, and defending pride’s territory – When females hear the roar of a female of another territory, they head to the area to attack – Some individuals always tend to lead the attack while others always seem to lag behind Territory Defense in Lions Territory Defense in Lions – Females cooperate in defending young against infanticidal males, hunting prey, and defending pride’s territory – When females hear the roar of a female of another territory, they head to the area to attack – Some individuals always tend to lead the attack while others always seem to lag behind

55. Reciprocal Altruism Territory Defense in Lions Territory Defense in Lions – Why are laggards tolerated? – It is not known but perhaps the laggards make up later by being exceptional hunters or good milk producers Social interactions are very complex and much needs to be learned about them to fully understand their natural selection Social interactions are very complex and much needs to be learned about them to fully understand their natural selection Territory Defense in Lions Territory Defense in Lions – Why are laggards tolerated? – It is not known but perhaps the laggards make up later by being exceptional hunters or good milk producers Social interactions are very complex and much needs to be learned about them to fully understand their natural selection Social interactions are very complex and much needs to be learned about them to fully understand their natural selection