Social cues and reproduction

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Social cues and reproduction

• social context greatly influences fertility
  status
• example dominant (alpha) male monkey and
  testosterone levels
• testosterone levels in male monkey among group of
  females
• significance gt communication is essential for
• mate selection
• distribution of resources
• repelling competitors
• producing viable young

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Role of social cues in regulating reproductive
behaviors

• some stimulate onset of breeding or affect
  release of gametes (e.g. induced ovulators)
• some influence gonadal maturation (e.g. male
  mouse pheromones can accelerate puberty in
  females)
• some support functions indirectly related to
  gamete production, rearing of young (e.g.
  establishment of territory)
• communication to facilitate parental care

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Pheromones

• pheromones play big role in mediating social cues
• example synchrony of ovulatory cycles
  (dormitory effect)
• signal (chemical) is release by glands that
  secrete onto surface of skin, into urine, saliva,
  feces
• signals are received by olfactory system
• mechanism of action is not understood from
  endocrine / neurological point of view

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Male-male Interactions

• male-male social cues involve forms of
  competition / aggression for
• access to female
• territory
• social status
• significance females tend to prefer dominant
  males
• behaviors greatly influenced by testosterone (T)
• decrease after castration resume T replacement
• show seasonal variability (e.g. rams)

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Male-male interactions, contd.

• behaviors are influenced by social context
• in mice, past experience (win vs. loss)
  influences future male / male encounters
• intact mice raised with castrates are more
  aggressive than those raised with other intact
  mice
• behaviors are influenced by environment (home
  territory)
• castrate mice on home territory will show signs
  of aggression towards intact intruder

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Male-male interactions, contd.

• sometimes expression of submissive behaviors is
  beneficial to an animal
• aggression and submission are distinct behaviors
  (not opposite)
• often used to avert repeated aggression
• not due to lack of androgens
• evidence castrate males dont show increased
  submissive behaviors
• adrenal glands may play a role
• experience defeat gt increase corticosterone
  production gt display submissive behavior

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Male-female interactions

• mainly mediated by pheromones
• allows gender discrimination
• female mice are more attracted to male urine
• more attracted to urine from dominant vs.
  subordinate male mouse
• estrous hamsters prefer urine of sexually
  experienced male
• allows recognition of mate (12 of mammals are
  monogamous)
• female hamsters show preference for urine of
  previous partner rather than new male

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Male-female interactions, contd.

• male pheromones can accelerate puberty in
  females
• female mice exposed to soiled bedding of male go
  through puberty 10 days earlier
• requires priming (3 days of exposure)
• window of opportunity 21-29 days
• effect is androgen-dependent (juvenile male urine
  doesnt have same effect)
• exposure to rams wool induces puberty in ewes
• male pheromones can synchronize female cycles
• introduce male mouse in cage of females gt
  synchronous estrous 3d later

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Male-female interactions, contd.

• male pheromones can terminate pregnancy
• expose pregnant female mouse to strange male
  (other than stud) gt pregnancy lost 3d later
• thought to be triggered by unfamiliar pheromone
• pheromone causes degeneration of corpus luteum in
  female gt pregnancy lost
• can prevent by administering progesterone
• probably triggered by same pheromone that
  accelerates puberty

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Female / Female Social CuesInhibition of puberty

• females can inhibit onset of puberty in other
  females
• puberty occurs later in mice reared in groups vs.
  those reared singly
• exposure of singly housed mouse to bedding soiled
  by other females has same effect (urine must be
  from females housed in groups)
• suggests role of pheromone
• some primates exhibit same phenomenon
• puberty-inhibiting pheromone not regulated by
  ovary (OVX gt still released)
• adrenals may regulate, since ADX blocks effect
• significance possible mechanism to regulate
  population growth

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Inhibition of puberty (female / female)

• studies re role in regulating population growth
  conducted on highway islands
• 1st gen. offspring of wild mice introd on island
• collected urine from mice on island where
  population was growing vs. island where
  population remained stable
• exposed prepubertal female lab mice to urine
• effect only urine from females in densely
  populated island had suppressive effect on
  puberty onset
• another expt introduced more females into
  established island (artificial population
  explosion)
• urine collected after explosion more effective
  in inhib. puberty than that collected before
  explosion

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Inhibition of puberty (female / female), contd.

• secretion of pub.-inhib. pheromone appears to be
  regulated itself by pheromones
• remove vomeronasal organ from female gt cant
  secrete pub.-inhib. pher. into urine
• mechanism of action of this pheromone?
• may increase norepinephrine, dopamine in
  mediobasal hypothalamus, since grouped females
  show higher levels of these neurotransmitters
• effect gt inhibition of GnRH?

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Female / Female InteractionsInfluences on
Ovulatory Cycles

• another social cue regulated by pheromones
  involves synchronization of ovulatory cycles
• female rats living together show synchrony of
  estrous cycles within 3 days (50-75)
• tracked as far as 12 cycles
• evidence suggests effect is mediated by
  pheromones
• females housed singly sharing same recirculated
  air exhibit synchrony
• two chemosignals have been identified to phase
  shift ovul. cycles
• one that phase advances cycle (shortens)
• one that phase delays (lengthens) cycle

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Female / FemaleSynchrony of Ovul. Cycles

• to test for phase advance vs. phase delay
  pheromones, presented isolated females daily with
  airborne odors from donor animals at specific
  cycle stage
• follicular phase odors shortened cycle (
  regulated)
• ovulatory odors lengthened cycle ( produced more
  variability)
• luteal odors had no effect
• source of pheromone undetermined
• human evidence of synchrony dormitory effect
• human pheromone in sweat? axillary (underarm)
  secretions can synchronize cycles

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Female / Female cuesAggressive social cues

• aggressive socials cues between females impact on
  fertility
• female hamsters aggressively defend home
  territory from other females on day prior to
  sexual receptivity
• adaptive significance?
• eliminate competition for mate?
• aggressive encounters can block pregnancy
• females often kill young of unrelated females
• role of testosterone in mediating female
  aggression being investigated

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Female to Male Social Cues

• female to male social cues provide precise
  information regarding the females reproductive
  state
• coordinates copulation with maximal fertility
• cues utilized
• aggression
• pheromones
• visual cues
• when studying female cues in laboratory
  environment, effects are sometimes masked due to
  close contact (greater chance of sexual arousal)

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Female / Male cues Pheromones

• male rodents prefer female odors
• odor of receptive female more attractive than
  nonreceptive female
• sexual experience in male is necessary for
  discrimination
• may be a learned behavior
• copulation may modify hormonal state of male
• attractant present in urine and vaginal discharge
• anosmia prevents courtship in male hamsters
• males prefer odors of estrous female over
  pregnant or lactating females
• adaptive significance pregnant, lactating
  females are aggressive also, energy not wasted
  on courtship of infertile female

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Female / Male Pheromones, contd.

• in hamsters, vaginal discharge is main
  chemoattractant
• apply vaginal discharge to hindquarters of
  another male gt other males attracted, display
  sexual behavior
• male monkeys also attracted to female odors in
  vaginal discharge
• secretion by female likely due to estrogen
• male will press bar repeatedly to gain access to
  OVX, E-treated female but not OVX female
• females can accelerate onset of male puberty in
  some species

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Female / Male Visual Cues

• female baboons exhibit swelling of sex skin
  during estrous
• attracts males from great distances
• exposure of nonreproductive male (not in breeding
  season) to female in estrous has profound
  effects
• dramatic increase in mounting, copulation
• testicular growth accelerated
• change in color of male sex-skin (T-dependent)
• increases blood T levels
• effect of female influenced by social context
• only 2 highest ranking males responded in this
  manner to estrous female