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2011-10-15

霊長類行動学9. 母子関係

霊長類行動学もくじ

The Primate Mother-Infant Bond

  • The fundamental social unit.
    • for example, even in "solitary" species (like Orangutan), mother-infant pairs are a stable social unit.

Relationship is of mutual benefit

  • benefit for children
    • Mother provides energy food (milk) until weaning age
      • Most カロリー comes from his/her mother
    • Mother provides movement (carrying around)
    • Mother provides protection (monitoring, restricting movement)
    • potential learning
    • Infant needs maternal contact for normal psychological development
      • (Harlow's experiments)
        • 3 conditions: wire mother with food, 暖かいmother without food, with food
        • if they are scared, then go to 温かいmother regardless the food
      • Bonobo pulls all hair out when stressed out..
  • benefit for the mother
    • Infant is mother's reproductive outlet

Variation in relationships among species

  • Taxonomic distinctions
    • Stepsirrhines: many "park" infants while foraging
      • Infant sleeps with mother, and is provided with food by mother, but mother leaves infant alone while foraging
      • Infant adopts behavior to minimize risk of predation.
      • e.g., Galago (bushbabies) - carry with mouth, Lemur
  • Particular distinctions between gregarious, nongregarious, and polyandrous species.
    • orangutans: mother is solitary with infant.
      • Infant stays with mother in travel and foraging
    • Juvenile and adolescent may stay with mother longer.
    • Callitrichids (Tamarinとか): infants cared for by resident males and siblings
      • Infants stay in group following weaning
      • Mortality of infants linked to care given by siblings and fathers, as well as mothers.
    • Gregarious species
      • Infants is raised in group
      • Mother is primary caregiver
      • Others in group handle infant ("allomothering")
      • Infants development has social component in interaction with other group members
      • Relationship with mother may persist or not depending on whether individual stays in group.

Weaning

  • Mother and infant break bond
  • Weaning involves interaction between maternal and infant effort to maintain bond
    • Mother initially possessive and protective of infant
    • Infant stays close to mother
      • Infant uses mother as a base to explore world
      • Infant begins to wander from mother more as time goes on
    • Infant begins to incorporate natural food progressively more and more, but still suckles
    • Mother will begin to reject infant attempts to suckle
      • Infant will cry, throw tantrums, get mother to concede
    • Eventually mother cuts off infant from suckling.
  • Whenever mother thinks cost for giving care to children go over the benefit, they try to stop children
  • Reason why children do not wean by themselves: they can take advantage of free foods under the care.
  • http://news.bbc.co.uk/1/hi/sci/tech/7934998.stm

Allomothering

  • Many gregarious primates show allomothering, or contact and care of infants by others
  • Allomothring is substitute mothering, but not the same bond
  • Allomothers will take and hold infant, sometimes protect and carry
  • Allomothers tend to be young (never reproduced), nulliparous, adult females
    • Older multiparous females show little interest in allomothering
  • infants sometimes have bright color like white or yellow, so that they can draw more attention.
  • Highly variable behavior among species - demonstrated in
  • reason for practice is unclear (various hypothesises)
    • Reduction of mom's time and effort.
    • Practice for new mothers
      • supported by observation that young females do it.
      • Inexperienced mothers make bad mothers
    • Status of allomother
      • Females prefer to handle high-ranking female's infants
      • May help young mothers integrate in social structure
    • Helps mother
      • Insurance policy if mother dies
      • Little evidence
    • Kin selected help for mother infant
      • Predicts that closely related individuals will be allomothers
      • Evidence is weak within groups-everydbody does it
      • Allomothering should be weak in non-female bonded species-weak evidence against it (e.g., Alouatta)
    • None of the above are mutually exclusive.

  • Sometimes allomothering is lethal
    • Allomother refuses to give up infant
    • Allomother neglects infant (drops, sits on, throw, twists, etc.)
    • Implies cost to allomother, implying a benefit
    • Occasionally orphans are adopted by siblings or other adults
      • Rare
      • Sisters will assume maternal role for older offspring
    • Sometimes other mothers abuse infants
      • usually associated with assertion of dominance, harassment.

Persistence of mother-offspring bond

  • Mother-infant bond can persist, even in non-gregarious species
    • Galagos adult female offspring will stay in or near mother's territory, effectively dividing it up, until new territory opens
      • Involves cost to mother in sharing resources
      • Help with contest competition between groups, but scramble competition among offspring.
  • Pongo, Pan: offspring associate closely with mother after weaning.
    • Often maintain ties into adulthood mutual support and association
  • Polyandrous species: offspring stay with parent and assist in rasing offspring until replace parent or leave
    • Kin selected altruism
    • Ultimate allomothering
  • Female-bonede species
    • Where females stay in troop, will often provide mutual assistance and support
    • Take on female rank in troop.

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