Kin Selection and Social Behavior

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Kin Selection and Social Behavior

• Interactions between individuals can have 4
  possible outcomes in terms of fitness gains for
  the participants.

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Kin Selection and Social Behavior

• Cooperation (mutualism) fitness gains for both
  participants.
• Altruism instigator pays fitness cost, recipient
  benefits.
• Selfishness instigator gains benefit, other
  individual pays cost.
• Spite both individuals suffer a fitness cost.

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Kin Selection and Social Behavior

• No clear cut cases of spite documented. The
  behavior clearly harms the instigator for no
  benefit so difficult to see how it could be
  favored by selection.
• Selfish and cooperative behaviors easily
  explained by selection theory because they
  benefit the instigator.

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The puzzle of altruism

• Altruism is hard to explain because the
  instigator pays a cost and another individual
  benefits.
• How can selection favor the spread of an
  altruistic allele that produces a behavior that
  benefits other individuals at the expense of
  individuals bearing the altruistic allele?

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• BTW when I say an allele that produces a
  behavior I dont mean that the allele literally
  directly codes for the behavior.
• An allele directly code for the structure of
  proteins.
• However, proteins interact with other proteins
  and the result of all these biochemical
  interactions in building a brain can result in an
  organism with one version of an allele behaving
  somewhat differently from an individual with a
  different version.

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The puzzle of altruism

• For Darwin altruism presented a special
  difficulty, which at first appears to me
  insuperable, and actually fatal to my whole
  theory.
• Darwin suggested however that if a behavior
  benefited relatives, it might be favored by
  selection.

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The puzzle of altruism

• W.D. Hamilton (1964) developed a model that
  showed how an allele that favored altruistic
  behavior could spread under certain conditions.

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Coefficient of relatedness

• Key parameter is the coefficient of relatedness
  r.
• r is the probability that the homologous alleles
  in two individuals are identical by descent (see
  earlier notes on inbreeding for the concept of
  identical by descentbasically copies of an
  allele being inherited from a particular
  individual).

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Calculating r

• Use a pedigree to calculate r.
• Pedigree shows all possible direct routes of
  hereditary connection between the two
  individuals.
• Because parents contribute half their genes to
  each offspring, the probability that alleles are
  identical by descent for each step is 50 or 0.5.

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Calculating r

• To calculate r
• (i) Trace each unique path between the two
  individuals via common ancestors and count the
  number of steps needed.
• (ii) For this path r 0.5 (number of steps).
  Thus, if two steps r for this path 0.5 (2)
  0.25.
• (iii) To calculate final value of r you add
  together the r values calculated from each path.

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Hamiltons rule

• Given r the coefficient of relatedness between
  the actor and the recipient, Hamiltons rule
  states that an allele for altruistic behavior
  will spread if
• Br - C gt0
• Where B is benefit to recipient and C is the cost
  to the actor. Unit of measurement for B and C is
  surviving offspring.

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Hamiltons rule

• Altruistic behaviors are most likely to spread
  when costs (C) are low, benefits (B) to recipient
  are high, and the participants are closely
  related (r is large).

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Applying Hamiltons rule

• You have a food item that is worth 2 units of
  benefit to you.
• You have a tiny nephew for whom the food would be
  worth 10 units of benefit.
• Should you eat the food or give it to your nephew?

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Applying Hamiltons rule

• The value of r for a nephew is ¼.
• Cost to you would be 2 (as youre giving up 2
  units of benefit).
• Benefit to nephew is 10.
• Is Br - C gt0?
• 10(¼) 2 ?
• 2.5 - 2 0.5. This is gt 0 so you should give the
  food to your nephew.
• Should you share with a cousin? r 1/8 for a
  cousin.

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• Share with a cousin?
• No because Br - C is not gt 0.
• 10 1/8 2 1.25 2 -0.75

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Inclusive fitness

• Hamilton invented the idea of inclusive fitness
  which divides an individuals fitness into two
  components
• Direct fitness results from an individuals
  personal reproduction (the babies it produces)
• Indirect fitness results from additional
  reproduction by relatives, that is made possible
  by an individuals actions. For example an
  individual might help feed its sisters offspring
  or guard them from predators.

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Kin selection

• Natural selection favoring the spread of alleles
  that increase the indirect component of fitness
  is called kin selection.

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Alarm calling in Beldings Ground Squirrels

• Giving alarm calls alerts other individuals but
  may attract a predators attention.
• Beldings Ground Squirrels give two different
  calls depending on whether predator is a
  predatory mammal (trill) or a hawk (whistle
  Sherman 1985).

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http//michaelfrye.com/yosemite-journal/?p375
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Is alarm calling altruistic?

• Sherman and colleagues observed 256 natural
  predator attacks.

https//www.flickr.com/photos/charlespan/652746514
5/
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Beldings Ground Squirrels

• In hawk attacks whistling squirrel is killed 2
  of the time whereas non-whistling squirrels are
  killed 28 of the time.
• Calling squirrel appears to reduce its chance of
  being killed.

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Beldings Ground Squirrels

• In predatory mammal attacks trilling squirrel is
  killed 8 of the time and a non-trilling squirrel
  is killed 4 of the time.

http//captainkimo.com/coyote-on-the-hunt-pouncing
-for-prey-at-yellowstone-national-park/
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Beldings Ground Squirrels

• Calling squirrel thus appears to increase its
  risk of predation.
• Whistling appears to be selfish, but trilling
  altruistic.

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Beldings Ground Squirrels

• Beldings Ground Squirrels breed in colonies in
  Alpine meadows.
• Males disperse, but female offspring tend to
  remain and breed close by. Thus, females in
  colony tend to be related.

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Beldings Ground Squirrels

• Sherman had pedigrees that showed relatedness
  among his study animals.
• Analysis of who called showed that females were
  much more likely to call than males.

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Beldings Ground Squirrels

• Females were also more likely than males to call
  when they had relatives within earshot.

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Beldings Ground Squirrels

• Relatives also cooperated in behaviors besides
  alarm calling.
• Females were much more likely to join close
  relatives in chasing away trespassing ground
  squirrels than less closely related kin and
  non-kin.

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Beldings Ground Squirrels

• Overall, data show that altruistic behavior is
  not randomly directed.
• It is focused on close relatives and should
  result in indirect fitness gains by increasing
  the survival prospects of these relatives and
  hence their future reproduction.

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Kin selection and cannibalism in tadpoles

• Spadefoot toad tadpoles come in two morphs.
• Typical morph is omnivorous mainly eats decaying
  plant material.
• Cannibalistic morph has bigger jaws and catches
  prey including other spadefoot tadpoles.

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Kin selection and cannibalism in tadpoles

• Pfennig (1999) tested whether cannibals
  discriminate between kin and non-kin.
• Placed 28 cannibalistic tadpoles in individual
  containers. Added two omnivorous tadpoles
  (tadpoles had never seen before) to each
  container. One was a sibling, the other non-kin.

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Kin selection and cannibalism in tadpoles

• Pfenning waited until cannibal ate one tadpole,
  then determined which had been eaten.
• Found that kin were significantly less likely to
  be eaten. Only 6 of 28 kin were eaten, but 22 of
  28 non-kin.

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Kin selection and cannibalism in tadpoles

• Pfennig also studied tiger salamanders whose
  tadpoles also develop into cannibalistic morphs.
• Kept 18 cannibals in separate enclosures in
  natural pond. To each enclosure added 6 siblings
  and 18 non-kin typical morph tadpoles.

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Kin selection and cannibalism in tadpoles

• Some cannibals discriminated between kin and
  non-kin. Others did not.
• Degree of relatedness to siblings 1/2

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Kin selection and cannibalism in tadpoles

• Thus, by Hamiltons rule discrimination in favor
  of kin favored if B(r) - C gt 0
• Benefit estimated by counting number of siblings
  that survived. Siblings of discriminating
  cannibals twice as likely to survive as siblings
  of non-discriminating cannibals.

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Kin selection and cannibalism in tadpoles

• Benefit thus approximately 2.
• Cost assessed by evaluating effect of not eating
  siblings by comparing growth of discriminating
  and non-discriminating cannibals. No difference
  in growth rates. Cost then estimated as close to
  0.

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Kin selection and cannibalism in tadpoles

• By Hamiltons rule discrimination should be
  favored because 2(1/2) - 0 1 which is gt0.

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Altruistic sperm in wood mice

• Moore et al. have demonstrated altruistic
  behavior by sperm of European wood mice.
• Females highly promiscuous. Males have large
  testes and engage in intense sperm competition
  with other males.

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Altruistic sperm in wood mice

• Wood mice sperm have hooks on their heads. And
  connect together to form long trains of sperm
  that can include thousands of sperm.
• Swimming together sperm travel twice as fast as
  if they swam separately.

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http//phenomena.nationalgeographic.com/2014/07/23
/these-mice-excel-at-assembling-the-ideal-sperm-sw
im-teams/
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Altruistic sperm in wood mice

• To fertilize egg, train must break up.
• To break up train many sperm have to undergo
  acrosome reaction releasing enzymes that usually
  help fertilize an egg.

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Altruistic sperm in wood mice

• Releasing these enzymes before reaching an egg
  means these sperm cannot fertilize the egg.
  These sperm sacrifice themselves.
• Because other sperm carry half of the same
  alleles, sacrifice makes sense in terms of kin
  selection.

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Discrimination against non-kin eggs by coots

• Important to avoid paying costs on behalf of
  non-kin.
• Lyon (2003) studied defense against nest
  parasitism in American coots.
• Coots often lay eggs in other coots nests in
  hopes of having them reared.

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Discrimination against non-kin eggs by coots

• Accepting parasitic eggs is costly because half
  of all chicks starve and same number reared in
  parasitized and non-parasitized nests.
• Thus, host parent loses one offspring for every
  successful parasite.

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Discrimination against non-kin eggs by coots

• Because of high cost of being parasitized and
  lack of benefit (assuming parasites are non-kin)
  Hamiltons rule predicts coots should
  discriminate against parasitic eggs.
• Coot eggs very variable in appearance. If 2 eggs
  laid within 24 hours Lyon knew one was a parasite.

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Discrimination against non-kin eggs by coots

• Among 133 hosts 43 rejected one or more
  parasitic eggs. Rejected eggs differed from
  hosts eggs significantly more than did accepted
  eggs.

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Discrimination against non-kin eggs by coots

• Females who accepted eggs laid one fewer egg of
  their own for each parasitic egg they accepted.
  Average total clutch (including parasites) 8
  eggs,

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Discrimination against non-kin eggs by coots

• Females who rejected eggs laid an average of 8 of
  their own eggs even though they waited to finish
  laying before disposing of eggs they were
  rejecting. Coots can count!
• By counting eggs and rejecting extras that do not
  look right coots prevent themselves from being
  parasitized.

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Parent-offspring conflict.

• Parental care is an obvious form of altruism. In
  many species parents invest huge quantities of
  resources in their offspring.
• Initially, parent and offspring agree that
  investment in the offspring is worthwhile because
  it enhances the offsprings prospects of survival
  and reproduction.

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Parent-offspring conflict.

• However, a parent shares only 50 of its genes
  with the offspring and is equally related to all
  of its offspring, whereas offspring is 100
  related to itself, but only shares 50 of genes
  with its siblings.
• As a result, at some point a parent will prefer
  to reserve investment for future offspring rather
  than investing in the current one, while the
  current offspring will disagree. This leads to a
  period of conflict called weaning.

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Parent-offspring conflict.

• The period of weaning conflict ends when both
  offspring and parent agree that future investment
  by the parent would be better directed at future
  offspring. This is when the benefit to cost
  ratio drops below ½.

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Fig 11.18
Figure shows B/C benefit to cost ratio of
investing in the current offspring. Benefit is
measured in benefit to current offspring and cost
is measured in reduction in future offspring.
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Parent-offspring conflict

• In instances where parents produce only half
  siblings we should expect weaning conflict to
  last longer because the current offspring is les
  closely related to future offspring.
• This has been confirmed in various field studies.

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Siblicide

• In many species there is intense conflict between
  siblings for food that may result in younger
  weaker chicks starving to death.
• In other species regardless of food supplies
  first hatched offspring routinely kill their
  siblings.

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Siblicide

• For example, in Black Eagles the first hatched
  chick hatches several days before its sibling.
  When the younger chick hatches its older sibling
  attacks and kills it.

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Siblicide

• In species such as Black Eagles siblicide is
  obligate in that the younger offspring is always
  killed. Black Eagles are only capable of rearing
  one young.
• The most likely explanation for the later hatched
  young is that for the parents it serves as an
  insurance offspring in case the first offspring
  fails to hatch or develop.

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Siblicide

• In other species such as Cattle Egrets there is
  intense conflict that establishes a clear
  age-based hierarchy in the brood that determines
  how food is divided among the brood members.
• In cattle egrets, younger chicks usually starve,
  but if it is a good food year they often fledge.

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Siblicide

• Siblicide is thus facultative in cattle egrets
  because restraint by the older chicks in not
  killing the younger siblings can be rewarded in
  good years.
• In Black Eagles there is no prospect of two young
  being reared, so the older chick ensures its own
  survival by eliminating its sibling.

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Siblicide

• Siblicide shows that relatedness does not
  necessarily lead to altruistic behavior. For
  Cattle Egrets and Black Eagles selfishness is
  better because the costs of altruism are too high.

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Reciprocal Altruism

• Some animals occasionally behave altruistically
  towards non-relatives.
• Such behavior is adaptive if the recipient is
  likely to return the favor in the future.

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Reciprocal altruism

• Reciprocal altruism most likely in social animals
  where individuals interact repeatedly because
  they are long-lived and form groups, and also
  when individuals have good memories.

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Reciprocal altruism in Vampire bats

• E.g. Vampire Bats. Feed on blood and share
  communal roosts.
• Bats may starve if they fail to feed several
  nights in a row.
• However, bats who have fed successfully often
  regurgitate blood meals for unsuccessful bats.

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Reciprocal altruism in Vampire bats

• Cost of sharing some blood is relatively low for
  donor bat but very valuable for recipient.
• Research shows that Vampire bats share with
  relatives, but also share with individuals who
  have shared with them previously and with whom
  they usually share a roost.

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Association is measure of how frequently two
individuals associate socially.
Regurgitators regurgitate to individuals
they associate with regularly.