A few points

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A few points

• Your quizzes
• Your Exam I
• Still on April 22
• Chapters 1, 2, 3, 4, 5, 6, 7, 10, and 11 (9
  chapters)
• Extra Credit 8 and 9
• Leaves 14 chapters

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Chapter 12 Family, Society, and Evolution

• Robert E. Ricklefs
• The Economy of Nature, Fifth Edition

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Background

• The behavior and, indirectly, life histories and
  ecological relationships of an individual are
  under strong selective pressure from
• the social and family environment
• relationship to members of both sexes
• For example, fitnesses of the male morphs of the
  side-blotched lizard are dependent on frequencies
  of other male morphs in the population
• these morphs interact through complex social
  interactions that determine reproductive success

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Background

• Individuals interact with other members of the
  same species throughout their lives.
• Each individual must perceive the behaviors of
  others and make appropriate responses
• some interactions pay benefits for cooperative
  behaviors because of a common interest
• interactions with kin (common evolutionary
  heritage)
• interactions with mates (common interest in
  success of offspring)

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• Insert figure 12.2

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Cooperation or Competition?

• All interactions between members of the same
  species delicately balance conflicting tendencies
  of cooperation and competition, altruism and
  selfishness.
• Such a balance is evident in humans, the most
  social of animals
• society is sustained by role specialization
• social life balances cooperation and conflict

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What is Social Behavior?

• Social behavior includes all interactions among
  individuals of the same species.
• These interactions range from cooperation to
  antagonism.
• Consequences of these interactions for
  individuals are substantial, with effects on
  individual fitness.

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Territoriality

• Any area defended by an individual against the
  intrusion of others may be regarded as a
  territory
• territories vary enormously in size and
  permanence
• animals are likely to maintain territories if
• the resource is defensible
• the rewards outweigh the cost of defense

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Dominance Hierarchies

• Defense of territories may not always be
  practical.
• In absence of territories, the outcome of
  conflict may be establishment of social rank.
• When individuals order themselves by social rank
  or status, the result is a dominance hierarchy.
• Social rank and occupancy of space may be
  directly related, as low-ranking individuals may
  be relegated to the periphery of a flock.
  (positive feedback loop)

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To fight or not to fight?

• Establishment of territories or social rank
  depends on the outcome of contests between
  individuals.
• In any confrontation, participants must weigh
• costs of fighting and benefits of winning
• likely outcome of the contest
• Determining optimal behavior is complicated by
  each individuals lack of knowledge about the
  behavior of the other participant.

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Optimal Behaviors and Game Theory

• Game theory analyzes the outcomes of behavioral
  decisions when these outcomes depend on the
  behavior of other players.
• Game theory predicts the individuals behavior
  based the best estimates of
• the other contestants response
• the reward for winning

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Advantages and Disadvantages of Living in Groups

• True social groups result from a purposeful
  joining together of (unrelated) individuals.
• Living in groups results in benefits and costs to
  flocking birds, like the European goldfinch
• benefit is less individual vigilance
• cost is the more rapid depletion of resources,
  forcing the flock to move more frequently

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• Insert figure 12.5

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Natural selection balances the costs and benefits
of behaviors.

• Toward a classification of behaviors
• Most social interactions can be broken into acts
  performed by
• donors - individuals initiating behaviors
• recipients - individuals toward whom behaviors
  are directed
• Each act has the potential to affect the
  reproductive success of both the donor and the
  recipient of the behavior

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A Classification of Behaviors

• Four combinations of fitness increments to donor
  and recipient lead to the following
  classification
• cooperation (benefits donor, selected for)
• selfishness (benefits donor, selected for)
• spitefulness (benefits no one, selected against)
• altruism (benefits recipient at cost to donor)
• Altruism, among these, is most problematic
• selfish behaviors would be expected to prevail
• yet altruistic acts are common in social species

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• Insert figure 12.6

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Kin selection favors altruistic behaviors.

• When an individual directs a behavior toward a
  sibling or other close relative, it influences
  the fitness of an individual with whom it shares
  more genes than it does with an individual drawn
  at random from the population.
• This special outcome of social behavior among
  relatives is called kin selection.

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Identity by Descent

• The likelihood that two individuals share copies
  of any particular gene is the probability of
  identity by descent, which varies by degree of
  relationship
• also called the coefficient of relationship
• full sibs have a 50 probability of sharing any
  gene
• parents and children also have 50 probability of
  sharing any gene, etc.
• Two cousins probability of 12.5 (1/8)

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A Model for Assessing Altruistic Behavior

• Total fitness of a gene responsible for a
  particular behavior is its inclusive fitness
• contribution to fitness of donor plus product of
  change in fitness to recipient X, weighted by
  coefficient of relationship
• a gene promoting altruistic behavior will have a
  positive inclusive fitness if
• C lt Br
• where C cost to donor
• B benefit to recipient
• r coefficient of relationship

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Implications of the Model

• Genes for altruistic behaviors should increase in
  the population when
• behaviors have low cost to donor
• behaviors are restricted to close relatives
• Opportunities for evolution of altruistic
  behaviors do exist
• individuals often associate in family groups
• individuals can often assess their relatedness

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Is guarding altruistic?

• Insert figure 12.10

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Cooperation among Individuals in Extended Families

• Complex relationships among extended human
  families are familiar to us
• often such families include only one
  child-producing pair
• a portion of the behavior of non-nuclear members
  of the extended family are directed toward
  well-being of these related children

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Cooperation in Bee-Eaters

• Extended families of bee-eaters exhibit
  cooperative and competitive behaviors
• selfish and selfless acts are directed toward
  others in direct accordance with the degree of
  relationship
• inclusive fitness is the appropriate measure of
  selection on social behavior
• altruistic behaviors can evolve among close
  relatives by kin selection
• Figure 12.13

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Cooperation Among Unrelated Individuals

• Social groups can form to promote mutual
  self-interest of unrelated individuals.
• Can groups of unrelated individuals move toward
  true cooperation?

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Game Theory and Cooperation

• The paradox
• conflict can reduce the fitness of selfish
  individuals below that of cooperative
  individuals, so cooperative behaviors should
  evolve among unrelated individuals
• but, when most of a social group consists of
  cooperative individuals, a selfish individual can
  achieve high fitness by cheating

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The Hawk-Dove Game

• The hawk-dove game (prisoners dilemma)
• a hawk always competes over resources, taking all
  the rewards when it wins
• 2 hawks always fight. Result on average one
  gets half the reward so the reward is ½ the
  average benefit minus the cost of fighting (1/2
  B-C)
• Hawk vs dove hawk gets it all
• the hawk strategy is not the best overall because
  hawks incur costs of conflict
• a dove never competes over resources, sharing
  resources with other doves, yielding them to
  hawks
• When 2 doves meet they share w/o cost 1/2B
• the dove strategy is the best overall because
  resources are shared without costs of conflict

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Hawks invade societies of doves.

• Dove behavior is not an evolutionarily stable
  strategy
• a population of doves is easily invaded (from an
  evolutionary perspective) by hawkish behavior
• a hawk in a population of doves reaps twice the
  rewards of doves
• a population of hawks is resistant to invasion by
  dove behavior, however

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Can hawks and doves coexist?

• When the benefit is less than twice the cost of
  conflict, dove behavior can invade a population
  of hawks.
• In this situation the proportion of hawks is
  one-half the ratio of the benefit to cost.
• Persistence of hawks and doves in this case is an
  evolutionarily stable mixed strategy.
• Each type of behavior can increase in frequency
  when it is rare thereby keeping both in the game

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Parents and offspring may come into conflict.

• Offspring consume parental resources, but this is
  desirable from the perspective of the parents
  when progeny thrive, so do the parents genes.
• Parents and offspring come into conflict when
  accumulation of resources by one offspring
  reduces the overall fecundity of its parents.

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Parents and offspring have different goals.

• Offspring try to resolve conflicts over resources
  in favor of their own reproductive success.
• For parents, a balanced approach to current and
  future reproduction is favored
• resources allocated to one offspring cannot be
  allocated to another
• resources allocated to current offspring reduce
  those that can be allocated to future offspring

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When does parent-offspring conflict occur?

• As young mature, the benefit to them of parental
  care declines.
• Because of coefficients of relationship among
  parents, an offspring, and that offsprings sibs
• when the benefit to parent of providing
  additional care falls below the cost of this care
  for future reproduction, the parent should cease
  providing care
• offspring should continue to request additional
  care until the benefit to parent of providing
  that care falls below twice the cost of this care
  for future reproduction

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Eusocial Insect Societies

• Social insects exhibit the extreme of family
  living, in which most offspring forego
  reproduction and help their parents raise
  siblings.
• This situation raises evolutionary questions
• how did such societies evolve?
• how can natural selection produce individuals
  with no individual fitness?

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What is eusociality?

• Eusociality entails
• several adults living together in groups
• overlapping generations
• cooperation in nest building and brood care
• reproductive dominance by one or a few
  individuals, including the presence of sterile
  castes
• Eusociality is limited among insects to Isoptera
  (termites) and Hymenoptera (ants, bees, wasps),
  and to one mammal, the naked mole rat.

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How did eusociality evolve?

• Potential sequence of evolutionary events
• parents have a lengthened period of care for
  developing brood (parents guard brood or
  provision larvae)
• parents live and continue to produce eggs after
  first progeny emerge
• offspring are in a position to help raise
  subsequent broods
• when progeny remain with their mother after
  adulthood, the way is open to relinquishing
  reproductive function to support mothers

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Organization of Insect Societies

• Insect societies are dominated by one or a few
  egg-laying females, queens
• queens of ants, bees, and wasps mate once and
  store sufficient sperm to produce a lifetime of
  offspring
• Nonreproductive progeny of the queen
• gather food and care for their developing
  brothers and sisters, some of which become
  sexually mature and leave the nest to mate
• Specific details vary somewhat for termite
  colonies, which are headed by a king and queen.

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Coefficients of Genetic Relationship in
Hymenoptera

• Hymenoptera have a haplodiploid sex-determining
  mechanism
• females (workers) develop from fertilized eggs
• males (drones) develop from unfertilized eggs
• Coefficients of genetic relationship are skewed
• female worker to female sibling is 0.75
• female worker to male sibling is 0.25
• queen to son or daughter is 0.5
• Sex ratios are female-biased, 31.

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Summary

• All behaviors have costs and benefits to the
  individual and to others affected by the
  behavior, with special consequences for close
  relatives.
• Behavior is influenced by genetic factors and is
  thus subject to evolutionary modification by
  natural selection.
• Interactions within a social setting lead to
  important evolutionary consequences when
  interests of individuals conflict or coincide.

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A few things extra

• Do the quiz for chapter 12. Due Friday (you get a
  bit extra time)
• Spend some time reading the more on the web
  section in this chapter
• Homework what can an understanding of ant
  genetics and behavior provide for us humans?
• Email me your thoughts by Friday midnight.