Intersexual selection continued

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Intersexual selection (continued)
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A species of hanging fly
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Hanging Fly Bittacus sp.
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Onward evolution of 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
• This act 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 more offspring produced by a relative.
• Actors fitness Increased through an increase in
  frequency of shared alleles.

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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 gt
  0.
• Natural selection favoring indirect fitness is
  called kin selection.

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• Calculating r
• e.g., siblings sharing two parents
• Each parent contributes ½ of its genes to each
  offspring
• P that allele b was transmitted from mother to an
  offspring is ½.
• P that the mother passed allele b to a sib is ½.
• P that both sibs got allele b from the mother ½
  x ½ 1/4
• Same probabilities obtain for getting allele b
  from the father.
• Therefore, r ¼ ¼ 2/4 0.5.

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• Two parents
• Add the probability that alleles are identical by
  descent through maternal pathway and the
  probability that alleles are identical by descent
  through the paternal pathway.
• 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.

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• Examples of altruism in social mammals

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Beldings ground squirrel Population dynamics of
colony
Predicted if alarms were given Randomly
Alarm call
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Females give alarm calls more frequently when a
close relative is nearby.
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Close relatives cooperate in defending territory
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