Chapter 11. Kin Selection and Social Behavior

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Chapter 11. 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.
• Selfish and cooperative behaviors easily
  explained by selection theory because they
  benefit the instigator.

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The puzzle of altruism

• Altruism is the difficult one to explain because
  the instigator pays a cost and another individual
  benefits.
• Hard to see how selection could favor an allele
  that produces behavior benefiting another
  individual at the expense of the individuals
  bearing the allele.

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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 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.

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Calculating r

• Need a pedigree to calculate r that includes both
  the actor and recipient and that shows all
  possible direct routes of connection between the
  two.
• Because parents contribute half their genes to
  each offspring, the probability that genes are
  identical by descent for each step is 50 or 0.5.

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Calculating r

• To calculate r one should trace each path between
  the two individuals and count the number of steps
  needed. Then for this path r 0.5 (number of
  steps)
• Thus, if two steps r for this path 0.5 (2)
  0.25.
• To calculate final value of r one adds 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 are low, benefits to recipient are
  high, and the participants are closely related.

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Inclusive fitness

• Hamilton invented the idea of inclusive fitness.
  Fitness can be divided into two components
• Direct fitness results from personal reproduction
• Indirect fitness results from additional
  reproduction by relatives, that is made possible
  by an individuals actions.

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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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Is alarm calling altruistic?

• Sherman and colleagues observed 256 natural
  predator attacks.
• 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.
• 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 marked animals and had pedigrees that
  showed relatedness among study animals.
• Analysis of who called showed that females were
  much more likely to call than males.

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Beldings Ground Squirrels

• In addition, females were more likely 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.

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Helping behavior in birdsWhite-fronted
Bee-eaters

• In a large number of birds young that are old
  enough to breed on their own instead help their
  parents rear siblings.
• Helpers assist in nest building, nest defense and
  food delivery.

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Helping behavior in birdsWhite-fronted
Bee-eaters

• Helping usually occurs in species where breeding
  opportunities are limited territories or nest
  sites are hard to acquire.
• Young make the best of a bad job by remaining
  home to assist their parents.

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Helping behavior in birdsWhite-fronted
Bee-eaters

• Steve Emlen et al. studied white-fronted
  bee-eaters intensively in Kenya.
• Nest in colonies of 40-450 individuals. Groups
  of relatives (clans) defend feeding territories
  in vicinity of colony.

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Helping behavior in birdsWhite-fronted
Bee-eaters

• First year birds that opt to help can choose
  among many relatives when deciding whom to help.
• Bee-eaters conform to predictions of Hamiltons
  rule.

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• Coefficient of relatedness determines whether a
  bee-eater helps or not.
• Also, bee-eaters choose to help their closest
  relatives.

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• Nonbreeders in clan that are not relatives (birds
  that have paired with members of the clan) are
  not related to offspring being reared and are
  much less likely to help than relatives.

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• Assistance of helpers is of enormous benefit to
  parents. More than 50 of bee-eater young starve
  before leaving the nest.
• On average, presence of each helper increases
  number of offspring successfully reared to
  fledging by 0.47. Thus, there is a clear
  inclusive fitness benefit.

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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
  (tadpole 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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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 off 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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The greenbeard effect

• Sometimes altruistic alleles help different
  alleles inadvertently when they help kin.
  However, behavior is still favored because it
  assists identical alleles half of the time.

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The greenbeard effect

• If alleles could recognize which individuals
  carried other copies of them then they could
  selectively act altruistically towards those
  individuals.
• Dawkins (1976) called this the greenbeard effect.
  

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The greenbeard effect

• Dawkins imagined an allele that caused its
  carriers to grow green beards, to recognize green
  beards in others and act altruistically towards
  them.
• Hard to imagine in wild because single allele
  must cause three different effects.

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The greenbeard effect

• However, Quellar et al. (2003) have described
  greenbeard effect in slime molds.
• Slime molds live in soil. Germinate from spores
  and spend most of life as independent,
  single-celled amoebae.

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Slime molds

• When food scarce, individuals signal each other
  chemically and aggregate together to form a
  slug-like mass.
• Slug travels some distance, then transforms into
  a tall, thin stalk with fruiting body on top.
• Cells in fruiting body form spores which disperse
  and begin cycle again.

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Slime molds

• Cells in stalk (20 of the individuals) sacrifice
  themselves.

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Slime molds

• Quellar et al. studied wild-type allele csA
• Allele codes for protein on cell surface of
  amoeba and that protein sticks to same protein on
  other amoebae. Allele thus codes for both trait
  and recognition (adhesion).

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Slime molds

• Remaining greenbeard trait is discriminating
  altruism.
• Quellar et al. mixed wild-type amoebae and
  amoebae carrying a knocked-out version of the csA
  allele and grew them on agar plates.
• Starved amoebae to induce slime molds to form
  fruiting bodies.

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Slime molds

• Quellar et al. found that wild-type cells were
  disproportionately represented in the stalk
  (suckers!) and knock-out type in the fruiting
  body.
• Wild-type apparently ended up in stalk because
  they stuck together better.

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Slime molds

• Situation reversed when slime molds grown on
  soil, their natural environment.
• More difficult for amoebae to stream on soil and
  wild-type can stick together and pull each other
  along.

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Slime molds

• Wild-type cells disproportionately represented in
  fruiting body as well as stalk.
• Less adhesive knockout cells tend to get left out
  of aggregations altogether.

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Slime molds

• Thus, in natural conditions wild-type allele of
  csA makes its carriers altruistic towards other
  wild-type cells.
• Kin selection thus works at level of individual
  alleles, not just individual organisms.

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Evolution of Eusociality

• Eusociality (true sociality).
• Many eusocial insects (bees, ants, termites) do
  not reproduce. Instead they act as helpers at
  parents nests for their entire life. This is an
  extreme type of altruism.

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Evolution of Eusociality

• Eusociality describes social systems with three
  characteristics
• Overlap in generations between parents and
  offspring.
• Cooperative brood care.
• Specialist castes of non-reproductive individuals.

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Haplodiploidy and eusocial Hymenoptera

• One idea advanced to explain eusociality is the
  unusual genetic system (Haplodiploidy) of the
  Hymenoptera (ants, wasps, bees, etc.).
• Males are haploid and females diploid.
• Males develop from unfertilized eggs and females
  from fertilized eggs.

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Haplodiploidy and eusocial Hymenoptera

• Daughters receive all of their fathers genes and
  half of their mothers genes. Thus, daughters
  share ¾ of their genes.
• This suggests females would be better off if they
  favored the production of reproductive sisters
  rather than their own offspring.

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Haplodiploidy and eusocial Hymenoptera

• Queens are equally related to all offspring and
  so should prefer a 11 ratio of sons to daughters
  among reproductives.
• Females workers however should prefer a 13 ratio
  of brothers to sisters among reproductives.

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Haplodiploidy and eusocial Hymenoptera

• It has been shown in wood ants that queens
  produce equal numbers of male and female eggs,
  but the hatching ratio is heavily female biased.
  Workers apparently selectively destroy male eggs.

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Haplodiploidy and eusocial Hymenoptera

• Haplodiploidy appears to influence worker
  behavior, but consensus today is that it does not
  explain evolution of eusocial behavior in
  Hymenoptera.
• There are several reasons why.

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Haplodiploidy and eusociality

• First, haplodiploid explanation assumes all
  workers have the same father. However, honeybee
  queens mate with more than 17 males on average.
• As a result relatedness between worker honeybees
  often below 1/3.

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Haplodiploidy and eusociality

• Second, in many species, more than one female
  founds a nest. In this case workers may be
  completely unrelated.

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Haplodiploidy and eusociality

• Third, many eusocial species are not haploid
  (e.g. termites) and many haplodiploid species are
  not eusocial.

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Haplodiploidy and eusociality

• Phylogenetic analysis of Hymenoptera by Hunt
  (1999) emphasizes that eusociality relatively
  rare even though haplodiploidy occurs in all
  groups.
• Eusociality occurs in only a few families which
  are scattered around the tree, which suggests
  eusociality has evolved independently multiple
  times.

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Haplodiploidy and eusociality

• Hunt also points out that eusociality has only
  evolved in groups that build complex nests, and
  care for young for a long time.
• Association between nest building, long term care
  and eusociality suggests main driving force for
  eusociality is ecological not genetic.

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Haplodiploidy and eusociality

• Nest building and need to supply offspring with a
  steady stream of food make it impossible or very
  difficult for a female to breed alone.
• Also, if predation rates are high, solitary
  breeding individuals may not live long enough to
  raise their young.

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Facultative strategies in paper wasps.

• Paper wasps (Polistes) are not sterile (unlike
  ant and bee workers). Females can nest with
  other females or establish their own nest.
• Nonacs and Reeve (1995) found in Polistes
  dominulus that females follow one of three
  strategies.

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Facultative strategies in paper wasps.

• Initiate own nest
• Join nest as a helper
• Wait for a nest to become available

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Facultative strategies in paper wasps.

• Individuals founding their own nest are very
  likely to fail because adult mortality is high
  and nests with multiple foundresses can keep the
  nest going.
• However in multifoundress nests there may be
  frequent conflict. The nests that did best were
  those where one female was markedly bigger than
  the others, which reduced fighting.

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Facultative strategies in paper wasps.

• The sit-and-wait strategy also can pay off
  because females often can adopt an orphaned nest
  or take one over late in the season.

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Facultative strategies in paper wasps.

• Overall, in paper wasps an individuals decision
  is affected by her relative size, relatedness to
  other females, and availability of unoccupied
  nests.

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Naked Mole-rats

• Naked mole-rats are highly unusual mammals.
• They are nearly hairless and ectothermic. They
  are eusocial and, like termites, can digest
  cellulose with the help of bacteria in their gut.

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Naked Mole Rats
Fig 51.33
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Naked Mole-rats

• The behavior of naked mole-rats is similar to
  that of colonial insects.
• There is a single reproductive female (queen) and
  1-3 reproductive males. The remaining
  individuals act as workers. They dig tunnels to
  find food, defend the tunnel system from other
  mole-rats, and tend the young.

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Naked Mole-rats

• Leading hypothesis for why naked mole-rats are
  eusocial is inbreeding.
• Average coefficient of relatedness is 0.81 and
  about 85 of matings are between parents and
  offspring or between full siblings.

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Naked Mole-rats

• Despite high level of relatedness conflicts still
  occur because reproductive interests of workers
  and reproductives are not identical.

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Naked Mole-rats

• Queens maintain control through physical
  dominance.
• Queen aggressively shoves workers who do not work
  hard enough and shoves are mainly directly
  towards less closely related individuals.
• Workers double their work rate after being
  shoved.

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Naked Mole-rats

• In addition to inbreeding, ecological factors
  such as severely limited breeding opportunities
  and group defense appear to contribute to
  eusociality in naked mole-rats.

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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.