Altruistic Behavior

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Altruistic Behavior
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Social Interactions

• Actor and Recipient
• Fitness possibilities (offspring units)
• 1. fitness of both actor and recipient decreases
  spiteful behavior (shouldnt occur)
  
• 2. both actor and recipient increase their
  fitness cooperative behavior
  
• 3. fitness of actor increases, fitness of
  recipient decreases selfish behavior
  
• 4. fitness of actor decreases fitness of
  recipient increases altruistic behavior.
  

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Altruistic Behavior

• The actor will perform an act
• places the actor at risk
• benefits the recipient
• Intuitively would appear to
• place the fitness of the actor in jeopardy
• increase the fitness of the recipient.
• Natural selection should eliminated altruistic
  acts.

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• Paradox resolved by inclusive fitness
• For social animals, two categories of fitness
• 1. direct fitness personal reproduction.
• But, because alleles are shared among relatives
• 2. indirect fitness assistance of actor results
  in greater success in raising relatives to
  reproductive maturity.
  
• Actors fitness increased by an increase in
  frequency of alleles shared with relatives.
  

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Social Behavior and Altruism

• Genetic model for altruism
• Coefficient of relatedness (r).
• probability that alleles in two individuals are
  identical by descent.
  
• B benefit to the recipient C cost to the
  actor
  
• measured in units of surviving offspring.
• Hamiltons rule an allele for altruistic
  behavior will increase in frequency if Br - C
  0.
  
• Natural selection favoring indirect fitness is
  called kin selection.
  

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• Calculating r
• Assume sexual reproduction
• siblings share two parents
• Each parent contributes ½ of its genes to each
  offspring
  
• Probability that an allele was transmitted from
  mother to an offspring is ½.
  
• Same probability (½) that the mother contributed
  the same allele to a sibling.
  
• Probability that both sibs got allele b from the
  mother ½ x ½ ¼
  
• Same probabilities obtain for getting that allele
  from the father.
  
• Therefore, r ¼ ¼ 2/4 0.5.

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• Two parents
• Two ways that identical alleles could have gotten
  into sibs.
  
• Maternal pathway
• Paternal pathway
• Either-or sum rule
• ¼ ¼ ½

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• Theoretically, the greater the value of r between
  actor and recipient, the greater the tendency to
  perform an altruistic act for that individual.
  
• Three independent events
• Only one path
• Product rule

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Social Insects With Haplo-diplo Sex Determination

• Queen daughters (workers) sons
• Mother B1/B2 Father B3
• Gametes ½ B1 ½ B2 All B3
• Chances that 2 gametes are alike
• Both B1 (½ x ½ ¼)
• Both B2 (½ x ½ ¼)
• Contribution to female offspring
• 50 of genes 50 of genes
• That alleles are alike in daughters
• ½ x 50 ¼ or 25
• Fitness of workers 25 50 75 or 0.75
• Fitness if workers reproduced 50 or 0.50

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Florida Scrub Jay
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(No Transcript)
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Altruism in social mammals
Beldings ground squirrel Population dynamics of
colony
Predicted if alarms were given randomly
Alarm call
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Observations of 30 attacks where ground squirrel
was killed (14 yrs.)

• Two types of warning calls
• A. in response to hawks (whistle)
• B. in response to land predators (trill).
• Mortality difference
• A. caller captured 2 of time
• B. caller captured 28 of time.
• A. hawk concentrates attacks on panicked
  individuals responding to whistle.
  
• B. land predator draws attention to itself.
• A. is selfish behavior
• B . Is altruistic behavior

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Females give alarm calls more frequently when a
close relative is nearby.
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Prairie dogs