A few pointsA few points

Your quizzes:Your quizzes:Your Exam IYour Exam I

Still on April 22Still on April 22 Chapters 1, 2, 3, 4, 5, 6, 7, 10, and 11 (9 Chapters 1, 2, 3, 4, 5, 6, 7, 10, and 11 (9

chapters)chapters) Extra Credit: 8 and 9Extra Credit: 8 and 9 Leaves 14 chaptersLeaves 14 chapters

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Chapter 12: Family, Chapter 12: Family, Society, and EvolutionSociety, and Evolution

Robert E. RicklefsRobert E. RicklefsThe Economy of Nature, Fifth EditionThe Economy of Nature, Fifth Edition

BackgroundBackgroundThe behavior and, indirectly, life histories The behavior and, indirectly, life histories

and ecological relationships of an and ecological relationships of an individual are under strong selective individual are under strong selective pressure from:pressure from: the social and family environmentthe social and family environment relationship to members of both sexesrelationship to members of both sexes

For example, fitnesses of the male morphs For example, fitnesses of the male morphs of the side-blotched lizard are dependent of the side-blotched lizard are dependent on frequencies of other male morphs in the on frequencies of other male morphs in the population:population: these morphs interact through complex social these morphs interact through complex social

interactions that determine reproductive successinteractions that determine reproductive success

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BackgroundBackgroundIndividuals interact with other members of Individuals interact with other members of

the same species throughout their lives.the same species throughout their lives.Each individual must perceive the behaviors Each individual must perceive the behaviors

of others and make appropriate responses:of others and make appropriate responses:some interactions pay benefits for cooperative some interactions pay benefits for cooperative

behaviors because of a common interest:behaviors because of a common interest: interactions with kin (common evolutionary interactions with kin (common evolutionary

heritage)heritage) interactions with mates (common interest in interactions with mates (common interest in

success of offspring)success of offspring)

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Insert figure 12.2Insert figure 12.2

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Cooperation or Competition?Cooperation or Competition?

All interactions between members of the All interactions between members of the same species delicately balance same species delicately balance conflicting tendencies of cooperation and conflicting tendencies of cooperation and competition, altruism and selfishness.competition, altruism and selfishness.

Such a balance is evident in humans, the Such a balance is evident in humans, the most social of animals:most social of animals:society is sustained by role specializationsociety is sustained by role specializationsocial life balances cooperation and conflictsocial life balances cooperation and conflict

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What is Social What is Social Behavior?Behavior?

Social behaviorSocial behavior includes all interactions among includes all interactions among individuals of the same species.individuals of the same species.

These interactions range from cooperation to These interactions range from cooperation to antagonism.antagonism.

Consequences of these interactions for individuals Consequences of these interactions for individuals are substantial, with effects on individual fitness.are substantial, with effects on individual fitness.

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TerritorialityTerritoriality

Any area defended by an individual Any area defended by an individual against the intrusion of others may be against the intrusion of others may be regarded as a regarded as a territoryterritory:: territories vary enormously in size and territories vary enormously in size and

permanencepermanenceanimals are likely to maintain territories if:animals are likely to maintain territories if:

the resource is defensiblethe resource is defensible the rewards outweigh the cost of defensethe rewards outweigh the cost of defense

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Dominance HierarchiesDominance HierarchiesDefense of territories may not always be Defense of territories may not always be

practical.practical. In absence of territories, the outcome of conflict In absence of territories, the outcome of conflict

may be establishment of social rank.may be establishment of social rank.When individuals order themselves by social rank When individuals order themselves by social rank

or status, the result is a or status, the result is a dominance hierarchydominance hierarchy..Social rank Social rank and and occupancy of space occupancy of space may be may be

directly related, as low-ranking individuals may directly related, as low-ranking individuals may be relegated to the periphery of a flock. (positive be relegated to the periphery of a flock. (positive feedback loop)feedback loop)

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To fight or not to fight?To fight or not to fight?

Establishment of territories or social rank Establishment of territories or social rank depends on the outcome of contests depends on the outcome of contests between individuals.between individuals.

In any confrontation, participants must In any confrontation, participants must weigh:weigh: costs of fighting and benefits of winningcosts of fighting and benefits of winning likely outcome of the contestlikely outcome of the contest

Determining optimal behavior is complicated Determining optimal behavior is complicated by each individual’s lack of knowledge about by each individual’s lack of knowledge about the behavior of the other participant.the behavior of the other participant.

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Optimal Behaviors and Optimal Behaviors and Game TheoryGame Theory

Game theoryGame theory analyzes the outcomes of analyzes the outcomes of behavioral decisions when these outcomes behavioral decisions when these outcomes depend on the behavior of other players.depend on the behavior of other players.

Game theory predicts the individual’s Game theory predicts the individual’s behavior based the best estimates of:behavior based the best estimates of: the other contestant’s responsethe other contestant’s response the reward for winningthe reward for winning

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Advantages and Disadvantages of Advantages and Disadvantages of Living in GroupsLiving in Groups

True social groups result from a purposeful True social groups result from a purposeful joining together of (unrelated) individuals.joining together of (unrelated) individuals.

Living in groups results in benefits and costs Living in groups results in benefits and costs to flocking birds, like the European goldfinch:to flocking birds, like the European goldfinch: benefit is less individual vigilancebenefit is less individual vigilance cost is the more rapid depletion of resources, cost is the more rapid depletion of resources,

forcing the flock to move more frequentlyforcing the flock to move more frequently

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Insert figure 12.5Insert figure 12.5

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Natural selection balances the costs Natural selection balances the costs and benefits of behaviors.and benefits of behaviors.

Toward a classification of behaviors:Toward a classification of behaviors: Most social interactions can be broken into acts Most social interactions can be broken into acts

performed by:performed by: donorsdonors - individuals initiating behaviors - individuals initiating behaviors recipientsrecipients - individuals toward whom behaviors - individuals toward whom behaviors

are directedare directed

Each act has the potential to affect the Each act has the potential to affect the reproductive success of both the donor and the reproductive success of both the donor and the recipient of the behaviorrecipient of the behavior

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A Classification of A Classification of BehaviorsBehaviors

Four combinations of fitness increments to Four combinations of fitness increments to donor and recipient lead to the following donor and recipient lead to the following classification:classification:1.1. cooperationcooperation (benefits donor, selected for) (benefits donor, selected for)2.2. selfishnessselfishness (benefits donor, selected for) (benefits donor, selected for)3.3. spitefulnessspitefulness (benefits no one, selected against) (benefits no one, selected against)4.4. altruismaltruism (benefits recipient at cost to donor) (benefits recipient at cost to donor)

Altruism, among these, is most problematic:Altruism, among these, is most problematic: selfish behaviors would be expected to prevailselfish behaviors would be expected to prevail yet altruistic acts are common in social speciesyet altruistic acts are common in social species

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Insert figure 12.6Insert figure 12.6

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Kin selection favors Kin selection favors altruistic behaviors.altruistic behaviors.

When an individual directs a behavior toward When an individual directs a behavior toward a sibling or other close relative, it influences a sibling or other close relative, it influences the fitness of an individual with whom it the fitness of an individual with whom it shares more genes than it does with an shares more genes than it does with an individual drawn at random from the individual drawn at random from the population.population.

This special outcome of social behavior This special outcome of social behavior among relatives is called among relatives is called kin selectionkin selection..

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Identity by DescentIdentity by DescentThe likelihood that two individuals share copies The likelihood that two individuals share copies

of any particular gene is the probabilityof any particular gene is the probability of of identity by descentidentity by descent, which varies by degree of , which varies by degree of relationship:relationship: also called the also called the coefficient of relationshipcoefficient of relationship full sibs have a 50% probability of sharing any full sibs have a 50% probability of sharing any

genegene parents and children also have 50% probability of parents and children also have 50% probability of

sharing any gene, etc.sharing any gene, etc. Two cousins probability of 12.5% (1/8)Two cousins probability of 12.5% (1/8)

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A Model for Assessing A Model for Assessing Altruistic BehaviorAltruistic Behavior

Total fitness of a gene responsible for a Total fitness of a gene responsible for a particular behavior is its particular behavior is its inclusive fitnessinclusive fitness:: contribution to fitness of donor plus product of contribution to fitness of donor plus product of

change in fitness to recipient X, weighted by change in fitness to recipient X, weighted by coefficient of relationshipcoefficient of relationship

a gene promoting altruistic behavior will have a a gene promoting altruistic behavior will have a positive inclusive fitness if:positive inclusive fitness if:

CC < < BrBrwhere:where: CC = cost to donor = cost to donor

BB = benefit to recipient = benefit to recipientrr = coefficient of relationship = coefficient of relationship

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Implications of the Implications of the ModelModel

Genes for altruistic behaviors should increase Genes for altruistic behaviors should increase in the population when:in the population when: behaviors have low cost to donorbehaviors have low cost to donor behaviors are restricted to close relativesbehaviors are restricted to close relatives

Opportunities for evolution of altruistic Opportunities for evolution of altruistic behaviors do exist:behaviors do exist: individuals often associate in family groupsindividuals often associate in family groups individuals can often assess their relatednessindividuals can often assess their relatedness

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Is guarding altruistic?Is guarding altruistic?

Insert figure 12.10Insert figure 12.10

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Cooperation among Individuals in Cooperation among Individuals in Extended FamiliesExtended Families

Complex relationships among extended Complex relationships among extended human families are familiar to us:human families are familiar to us: often such families include only one child-often such families include only one child-

producing pairproducing pair a portion of the behavior of non-nuclear a portion of the behavior of non-nuclear

members of the extended family are directed members of the extended family are directed toward well-being of these related childrentoward well-being of these related children

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Cooperation in Bee-Cooperation in Bee-EatersEaters

Extended families of bee-eaters exhibit Extended families of bee-eaters exhibit cooperative and competitive behaviors:cooperative and competitive behaviors: selfish selfish andand selfless acts are directed toward selfless acts are directed toward

others in direct accordance with the degree of others in direct accordance with the degree of relationshiprelationship

inclusive fitness is the appropriate measure of inclusive fitness is the appropriate measure of selection on social behavior:selection on social behavior: altruistic behaviors can evolve among close altruistic behaviors can evolve among close

relatives by kin selectionrelatives by kin selection Figure 12.13Figure 12.13

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Cooperation Among Cooperation Among Unrelated IndividualsUnrelated Individuals

Social groups can form to promote mutual Social groups can form to promote mutual self-interest of unrelated individuals.self-interest of unrelated individuals.

Can groups of unrelated Can groups of unrelated individuals move toward true individuals move toward true cooperation?cooperation?

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Game Theory and Game Theory and CooperationCooperation

The paradox:The paradox:conflict can reduce the fitness of selfish conflict can reduce the fitness of selfish

individuals below that of cooperative individuals below that of cooperative individuals, so cooperative behaviors individuals, so cooperative behaviors should evolve among unrelated individualsshould evolve among unrelated individuals

but,but, when most of a social group consists of when most of a social group consists of cooperative individuals, a selfish individual cooperative individuals, a selfish individual can achieve high fitness by cheatingcan achieve high fitness by cheating

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The Hawk-Dove GameThe Hawk-Dove Game The hawk-dove game (prisoner’s dilemma):The hawk-dove game (prisoner’s dilemma):

a hawk always competes over resources, taking all the a hawk always competes over resources, taking all the rewards when it wins:rewards when it wins: 2 hawks always fight. Result – on average – one gets half the 2 hawks always fight. Result – on average – one gets half the

reward so the reward is ½ the average benefit minus the reward so the reward is ½ the average benefit minus the cost of fighting (1/2 B-C)cost of fighting (1/2 B-C)

Hawk vs dove: hawk gets it allHawk vs dove: hawk gets it all the hawk strategy is not the best overall because hawks the hawk strategy is not the best overall because hawks

incur costs of conflictincur costs of conflict a dove never competes over resources, sharing resources a dove never competes over resources, sharing resources

with other doves, yielding them to hawks:with other doves, yielding them to hawks: When 2 doves meet – they share w/o cost: 1/2BWhen 2 doves meet – they share w/o cost: 1/2B the dove strategy is the best overall because resources are the dove strategy is the best overall because resources are

shared without costs of conflictshared without costs of conflict

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Hawks invade societies Hawks invade societies of doves.of doves.

Dove behavior is not an Dove behavior is not an evolutionarily evolutionarily stable strategystable strategy:: a population of doves is easily invaded (from an a population of doves is easily invaded (from an

evolutionary perspective) by hawkish behavior:evolutionary perspective) by hawkish behavior: a hawk in a population of doves reaps twice the a hawk in a population of doves reaps twice the

rewards of dovesrewards of doves a population of hawks a population of hawks isis resistant to invasion by resistant to invasion by

dove behavior, howeverdove behavior, however

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Can hawks and doves Can hawks and doves coexist?coexist?

When the benefit is less than twice the cost of When the benefit is less than twice the cost of conflict, dove behavior can invade a population of conflict, dove behavior can invade a population of hawks.hawks.

In this situation the proportion of hawks is one-In this situation the proportion of hawks is one-half the ratio of the benefit to cost.half the ratio of the benefit to cost.

Persistence of hawks and doves in this case is an Persistence of hawks and doves in this case is an evolutionarily stable evolutionarily stable mixed strategymixed strategy..

Each type of behavior can increase in frequency Each type of behavior can increase in frequency when it is rare – thereby keeping both in the when it is rare – thereby keeping both in the gamegame

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Parents and offspring Parents and offspring may come into conflict.may come into conflict.

Offspring consume parental resources, but Offspring consume parental resources, but this is desirable from the perspective of the this is desirable from the perspective of the parents: when progeny thrive, so do the parents: when progeny thrive, so do the parents’ genes.parents’ genes.

Parents and offspring come into conflict when Parents and offspring come into conflict when accumulation of resources by one offspring accumulation of resources by one offspring reduces the overall fecundity of its parents.reduces the overall fecundity of its parents.

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Parents and offspring Parents and offspring have different goals.have different goals.

Offspring try to resolve conflicts over Offspring try to resolve conflicts over resources in favor of their own resources in favor of their own reproductive success. reproductive success.

For parents, a balanced approach to For parents, a balanced approach to current and future reproduction is favored:current and future reproduction is favored: resources allocated to one offspring cannot be resources allocated to one offspring cannot be

allocated to anotherallocated to another resources allocated to current offspring reduce resources allocated to current offspring reduce

those that can be allocated to future offspringthose that can be allocated to future offspring

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When does parent-When does parent-offspring conflict occur?offspring conflict occur?As young mature, the benefit to them of As young mature, the benefit to them of

parental care declines.parental care declines.Because of coefficients of relationship among Because of coefficients of relationship among

parents, an offspring, and that offspring’s sibs:parents, an offspring, and that offspring’s sibs: when the benefit to parent of providing additional when the benefit to parent of providing additional

care falls below the cost of this care for future care falls below the cost of this care for future reproduction, the parent should cease providing carereproduction, the parent should cease providing care

offspring should continue to request additional care offspring should continue to request additional care until the benefit to parent of providing that care falls until the benefit to parent of providing that care falls below twice the cost of this care for future below twice the cost of this care for future reproductionreproduction

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Eusocial Insect Eusocial Insect SocietiesSocieties

Social insects exhibit the extreme of family Social insects exhibit the extreme of family living, in which most offspring forego living, in which most offspring forego reproduction and help their parents raise reproduction and help their parents raise siblings.siblings.

This situation raises evolutionary questions:This situation raises evolutionary questions: how did such societies evolve?how did such societies evolve? how can natural selection produce individuals how can natural selection produce individuals

with no individual fitness?with no individual fitness?

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What is eusociality?What is eusociality?EusocialityEusociality entails: entails:

several adults living together in groupsseveral adults living together in groups overlapping generationsoverlapping generations cooperation in nest building and brood carecooperation in nest building and brood care reproductive dominance by one or a few individuals, reproductive dominance by one or a few individuals,

including the presence of sterile including the presence of sterile castescastes

Eusociality is limited among insects to Eusociality is limited among insects to Isoptera (termites) and Hymenoptera (ants, Isoptera (termites) and Hymenoptera (ants, bees, wasps), and to one mammal, the naked bees, wasps), and to one mammal, the naked mole rat.mole rat.

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How did eusociality How did eusociality evolve?evolve?

Potential sequence of evolutionary events:Potential sequence of evolutionary events:parents have a lengthened period of care for parents have a lengthened period of care for

developing brood (parents guard brood or developing brood (parents guard brood or provision larvae)provision larvae)

parents live and continue to produce eggs after parents live and continue to produce eggs after first progeny emergefirst progeny emerge

offspring are in a position to help raise offspring are in a position to help raise subsequent broodssubsequent broods

when progeny remain with their mother after when progeny remain with their mother after adulthood, the way is open to relinquishing adulthood, the way is open to relinquishing reproductive function to support mother’sreproductive function to support mother’s

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Organization of Insect Organization of Insect SocietiesSocieties

Insect societies are dominated by one or a few Insect societies are dominated by one or a few egg-laying females, egg-laying females, queensqueens:: queens of ants, bees, and wasps mate once and store queens of ants, bees, and wasps mate once and store

sufficient sperm to produce a lifetime of offspringsufficient sperm to produce a lifetime of offspringNonreproductive progeny of the queen:Nonreproductive progeny of the queen:

gather food and care for their developing brothers gather food and care for their developing brothers and sisters, some of which become sexually mature and sisters, some of which become sexually mature and leave the nest to mateand leave the nest to mate

Specific details vary somewhat for termite Specific details vary somewhat for termite colonies, which are headed by a king and colonies, which are headed by a king and queen.queen.

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Coefficients of Genetic Coefficients of Genetic Relationship in HymenopteraRelationship in Hymenoptera

Hymenoptera have a haplodiploid sex-Hymenoptera have a haplodiploid sex-determining mechanism:determining mechanism: females (workers) develop from fertilized eggsfemales (workers) develop from fertilized eggs males (drones) develop from unfertilized eggsmales (drones) develop from unfertilized eggs

Coefficients of genetic relationship are Coefficients of genetic relationship are skewed:skewed: female worker to female sibling is 0.75female worker to female sibling is 0.75 female worker to male sibling is 0.25female worker to male sibling is 0.25 queen to son or daughter is 0.5queen to son or daughter is 0.5

Sex ratios are female-biased, 3:1.Sex ratios are female-biased, 3:1.36

SummarySummaryAll behaviors have costs and benefits to the All behaviors have costs and benefits to the

individual and to others affected by the individual and to others affected by the behavior, with special consequences for behavior, with special consequences for close relatives.close relatives.

Behavior is influenced by genetic factors and Behavior is influenced by genetic factors and is thus subject to evolutionary modification is thus subject to evolutionary modification by natural selection.by natural selection.

Interactions within a social setting lead to Interactions within a social setting lead to important evolutionary consequences when important evolutionary consequences when interests of individuals conflict or coincide.interests of individuals conflict or coincide.

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A few things A few things extra extra

- Do the quiz for chapter Do the quiz for chapter 12. Due Friday (you get 12. Due Friday (you get a bit extra time)a bit extra time)

- Spend some time Spend some time reading the ‘more on reading the ‘more on the web’ section in this the web’ section in this chapterchapter

- Homework: what can an Homework: what can an understanding of ant understanding of ant genetics and behavior genetics and behavior provide for us humans?provide for us humans?

- Email me your thoughts Email me your thoughts by Friday midnight.by Friday midnight.

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