Kin selection and the evolution of social behavior

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Kin selection and the evolution of social behavior
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Evolution of altruism

• If natural selection is based on individual
  advantage, why are some organisms apparently
  altruistic

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Sterile castes Helpers at nest
Alarm calls
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Altruistic behavior

• Darwin considered altruistic behavior a special
  difficulty, which at first appeared to me
  insuperable, and actually fatal to my whole
  theory.
• But Darwin recognized that selection could favor
  altruistic behavior if it benefited close
  relatives of the altruist.

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Inclusive fitness

• An important concept to explain altruistic
  behavior
• First was discussed by R.A. Fisher and J.B.S.
  Haldane (two of the founders of population
  genetics)
• Developed in detail by W. Hamilton in 1964

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Inclusive Fitness

• Fate of allele depends on its effect on fitness
  of the individual carrying it (direct fitness).
• And its effect on fitness of other individuals
  carrying the same allele (indirect fitness).
• Individuals most likely to carry the same alleles
  are relatives.
• Selection based on indirect fitness effects has
  come to be known as kin selection.

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• Most obvious example of a trait that has evolved
  by kin selection is parental care.
• If allele A causes a parent to provide care to
  offspring, those offspring will have a higher
  probability of survival.
• The A allele will probably have costs for the
  parent.
• Benefit must outweigh the cost in order for A
  allele to increase in frequency.

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• Allele A increases in proportion to benefit
  provided to individual performing the behavior
  and to other individuals bearing the A allele.
• Allele A decreases in proportion to the cost of
  the altruistic action to bearers of the allele.
• ai is base fitness of an individual with genotype
  i in the absence of social interactions
• ci is the cost (deleterious effect) of altruistic
  behaviors to an individual with genotype i.
• bij is the increase in fitness of an individual
  with genotype j due to the altruistic behavior of
  individuals with genotype i.
• rij is the degree to which the performer of the
  altruistic behavior, and the recipient share the
  same alleles.

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If altruism is costly to the altruist, then, for
A to increase
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r probability of identity by descent of alleles
in two different individuals
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Asked whether he would lay down his life for his
brother, the biologist J.B.S. Haldane responded,
"Nobut for two brothers or eight cousins."
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• Q if the cost of an altruistic behavior
  (caused by allele A) is the death of the altruist
  (cost 1.0), and the benefit of the altruistic
  act to a full sibling is to increase its fitness
  by 50 (benefit 0.5), how many full sibs would
  have to receive the benefit in order for the
  altruistic allele to increase in frequency?
• A

Good way to think of this is ?rb - c gt 0. So x (
siblings) rb - c gt 0 x0.50.5 - 1 gt 0
0.25x - 1 gt 0 x gt 4 Must be at least 5
full-sibs benefitting to make this allele spread
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• Altruism is more likely to evolve if the behavior
  can be preferentially directed towards relatives.
• How can a behavior be preferentially directed
  towards relatives?

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A note of caution in thinking about inclusive
fitness and altruism

• Critics of inclusive fitness theory have often
  assumed that it requires animals to make complex
  calculations and be aware of wanting to spread
  their genes.
• Its not true. An organism doesnt have to know
  if its actions increase its fitness, or why. It
  just does what it does, and thats either favored
  by selection or not.

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Classic altruistic behaviors

• Alarm calling
• Helping at the nest
• Eusociality

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Alarm calls in Beldings ground squirrels
Males disperse. Females remain in natal
area. Females in proximity tend to be related.
Sherman (1977)
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Calling more likely when kin are near
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Kin cooperate to expel intruders
Freq different kinds of kin helped a territorial
female to chase an intruder
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Helpers at the nest white-fronted bee eaters
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Helpers at the nest white-fronted bee eaters
Relatedness of helpers to nestlings
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Eusociality

• Cooperation in caring for young
• Reproductive division of labor w/ some sterile
  individuals
• Overlap of generations so that offspring help
  parents

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Eusocial species
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• Hamilton proposed that unique sex-determination
  system of hymenoptera predisposed them to
  eusociality.
• What system?

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Haplodiploidy
Mother-daughter r 1/2 Full sisters r (1/2 x
1) (1/2 x 1/2) 3/4
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However

• If female workers have the different fathers,
  advantage declines. Queen honey bees mate with 17
  males on average. Average r among workers lt 0.33
• In many species more than one queen is active in
  founding a nest. If so, many workers in the
  colonies have a coefficient of relatedness of 0.
• Many eusocial species are not haplodiploid
  (termites, naked mole rats, some beetles and
  bugs), and many haplodiploid species are not
  eusocial (parasitic wasps, taratula hawks, cicada
  killers, sawflies, mud daubers).

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Adults care for larvae for extended periods
Complex nest building
Hunt (1999)
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If we have time

• Id like to go back to discuss sexual selection
  v. ecological selection.

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Other interactions of ecology and sexual selection

• Evolution of sexually-selected trait can be
  modified by ecological selection

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Tungara Frog
Call consists of whine and chuck
The fringe-lipped bat also prefers chuck!
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Guppies
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Guppy Predators
Small predators
Large predators
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Results of Endlers Experiment
R Rivulus present (small predator) C Cichlid
present (large predator) K no
predator Predators introduced at time S.