霊長類行動学15. オスメス間の戦略

霊長類行動学もくじ

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
    • e.g., Gorilla - female can leave a group
  • 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
    • which forced female to be promiscuity
• 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.