Sociality and kin selection in insects

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Sociality and kin selection in insects

• ??? (Ayo)
• ?????? ???????

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Contents

• 9.1 introduction
• 9.2 The origin and evolution of eu-sociality
  (????)
• 9.3 The evolution of a stable reproductive skew
• 9.4 Sex ratio evolution and kin conflict in
  social insects
• 9.5 conclusion

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9.1 Introduction

• Eusocial society(???????) alongside cooperative
  care of the brood and an overlap of adult
  generations, exhibit a reproductive division of
  labour (???????).
• Some members are specialized for reproduction
  (queens or kings), whereas others devote
  themselves to foraging, nest construction,
  defence and brood-reaing.
• Reproductive altruism (??????)

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Eusocial insects

• Most eusocial insects belong to two orders, the
  Hymenoptera (???) (ants, bees and wasps) and the
  Isoptera (termites) (??).
• All ants and termites are eusocial, but many bees
  and wasps are solitary or exhibit other grades of
  social organization.
• A number of aphids (Hemiptera) are arguably also
  eusocial, as are some beetles and thrips.
• Table 9.1 The major groups of eusocial insects
  and their traits.

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Hamiltons rule

• Hamiltons theory of kin selection.
• the evolution of altruism and sociality
• Hamiltons rule, the gene for altruism undergoes
  selection if the condition r1b - r2c gt 0 is
  satisfied.
• r1 is the altruists relatedness to the
  beneficiarys offspring (?????) x b(???)
• r2 is the altruists relatedness to its own
  offspring. (????????) x c (???)

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• West-Eberhard (1975), ? Hamiltons rule ??? if rb
  c gt 0, where r is the relatedness of the
  altruist to the beneficiary.
• Table 9.2 Relatedness levels in a social insect
  colony.

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9.2 The origin and evolution of eusociality

• 9.2.1 The necessity of kin selection
• 9.2.2 Hymenopteran eusociality and the
  haplodiploidy(????) hypothesis
• 9.2.3 The origin of eusociality in the termites

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The necessity of kin selection

• Reciprocal altruism(????) is not true
  altruism.
• Eusociality usually entails true altruism
  (?????).
• Hamiltons rule shows that both genetic factors
  (affecting relatedness) and ecological ones
  (affecting benefit and cost) must be important in
  promoting eusocial evolution.
• Eusocial evolution Mutualism hypothesis vs.
  parental manipulation hypothesis

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Hymenopteran eusociality and the haplodiploidy
hypothesis

• Eusociality has evolved independently many times
  among the insects.
• Wilson (1971) estimated that there have been 11
  origins of eusociality in the Hymenoptera, and
  one in the termites.
• A phylogeny based on mitochondrial DNA sequences
  suggests that the aphid family Hormaphididae
  evolved a a soldier caste at least five times.

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Relatedness levels in the Hymenoptera

• Males are haploid and develop from unfertilized
  eggs, but females are diploid and develop from
  fertilized eggs. (haplo-diploidy)
• ??,?? ? relatedness ????
• Haplo-diploidy hypothesis

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9.3 The evolution of a stable reproductive skew

• Skew theory suggest several factors of this type.
• Fig. 9.2 factors affect the stable level of
  reproductive skew.
• ?? reproductive skew???Group productivity,
  ecological constraints, relatedness
• ????? subordinate fighting ability

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Skew evolution in the polistine wasps

• Reeve and Nonacs (1992) Polistes fuscatus wasps,
  skew reproduction, ?????,alpha, beta
• ?????? eggs
• Alpha queens showed no consistent response to egg
  removal, but beta ones became more aggressive on
  average.

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Skew evolution in the leptothoracine ants

• Bourke and Heinze (1994), polygynous colonies
  live in extended uniform habitats such as
  pinewoods.
• Cost of dispersal are therefore relatively low.
• All queens lay eggs and live together peaceably.
  (skew is low)
• Monogynous colonies live in a rocky area.
• Cost of dispersal is high.
• Permanently wingless, only one queen.

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9.4 Sex ratio evolution and kin conflict in
social insects

• Relatedness asymmetry relateness to systers /
  relatedness to brothers
• 0.75/0.25 31 (Table 9.2)
• Sex ratio 31 in favour of females.
• Tests of sex ratio theory in social Hymenoptera
• Table 9.4 Tests of sex ratio theory within
  monogynous, non-parasitic ant species.
• Population sex investment ratio
  ????????(gt0.5),?????? (0.36)

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• Some colonies at mother-daughter associations
  should produce female-biased broods.
• Sundstrom (1994), monogynous population of wood
  ant (Formica truncorum), using allozyme analysis.
• Some colonies had a multiply mated queen,
  produced mostly males
• Others had a singly mated queen produced mainly
  females.

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How workers manipulate sex allocation

• Sundstrom et al. (1996) shown that all queens in
  a monogynous population of Formica exsecta
  contributed a similar fraction of haploid eggs to
  their colonys egg pool.
• However, workers in colonies headed by singly
  mated queens raised a female bias of adult
  sexuals,
• Whereas workers under multiply mated queens
  raised a male bias.

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9.5 conclusion

• Two unsolved issues
• The adaptive significance of within-colony kin
  discrimination
• The evolution of multiple mating.

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