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霊長類行動学15. オスメス間の戦略


the strategy can be categorized into the following four:

  • 1. Male tactics relative to male
  • 2. Female tactics relative to male
  • 3. male tactics relative to female
  • (female tactics relative to female is very limited)
  • both males and females care only self-interest
    • each has own mating tactics to maximize their reproductive success
    • keep changing strategies until it becomes stable

1. male tactics relative to male

male distribution
  • relative to female distribution
  • why some primate forms single male group?
    • because he can guard the female.
  • why most of the other primate males group together?
    • i.e., allow other male to stay in the same group?
    • they seek for immediate benefit by costing long-term risk

what is the cost for males to stay together?
  • establishing male dominance hierarchy
    • risk for injury, stress, competition
    • possible solution for them
      • stay quietly in the group to invest for future reproductive success.
        • e.g., Gorilla or Galago
        • but still have a risk of predation and less chance.
  • in large multi-male group
    • tolerant a presence of only a certain number of males.
    • if the group get bigger, low ranking males should leave because he wouldn't have a chance to mate for long time, but they DON'T
      • because too difficult to find other group by roaming around the dangerous savanna
      • even if they find, there is no guarantee that the new group has less males.

model to explain the reason why they don't leave, who control the mating
  • 1. concession model
    • dominant benefits from presence of subordinate males.
      • they can help dominant male to defend the group
      • so, he concedes enough mating to keep subordinates around.
    • e.g., Baboon
    • reproductive skew
      • increase with relatedness
  • 2. restraint model
    • dominant male controls group membership
    • subordinate male controls mating.
    • non-eviction
    • compromise - 'tag of war' (主権争い)
      • reproductive skew should decrease with relatedness
        • Chimp are related

2. female tactics relative to male

  • female has to adjust behavior of males, especially old world monkey
  • male can coerce female
two set of tactics
  • 1. Premating tactics
    • A. Promiscuity: female needs only one to reproduce, need a reason to be promiscuity
      • a. estrus synchrony - over-rap estrus
        • male cannot guard multi-mate at a time
      • b. behavior
        • sex skins - ovulation season to be uncertain
    • B. Mate preference
      • not only a mate-choice
      • makes it possible to mate guarding easy
      • she guarantees. paternity-males guard offspring
    • C. female transfer
    • D. female regulation of group size
      • large groups attract males
  • 2.Post mating tactics
    • more success rate of implantation at orgasm
      • "upsuck hypothesis"
          • suggests that the orgasm actually helps pull the sperm up into the reproductive tract with muscle contractions.
      • easily reach orgasm when mating with preferred male
    • female can time mating partner
    • for other animals
      • female discharges sperms by changing PH
      • change the diameter of the entrance

Male tactics relative to male

  • 1) infanticide
    • way to force female to mate
  • 2) dominant will target mate guarding
    • carefully watching females to maximize their reproductive success
  • 3) male can cooperatively guard females
  • 4) male can use social strategies to encourage female-choice
    • e.g., Baboon, to make friend with females.



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