霊長類行動学12. オスとメスの関係パターン
male-female interactions
- mating
- primate-male occur with group (odd in animals)
- female concerns male only as a mate
- except Marmoset - expect them to take care of child
- What people think Human male provide
- resources?
- protection? - really? from what?
- primate male does not protect by fighting females
- there is an evidence that Baboon males even run away faster than females when they are in danger
Male association with females
- 1. Access to mates partners
- females need partner, too.
- 2. Access to resources
- females disperse based on food availability
- so male get benefit from going to female place so that he can also get access to food
- bad for females
- 3. protection from predators ※but not fight
- need to be wathful from
- on tree -> raptor like eagles
- on ground -> lepard etc
- need to be wathful from
- 4. male parental care (some male can care)
- usually males don't do anything, but sometimes.
- 5. male threat
- male coersion for mating
- male forcing female to mate with him
- costly behavior - in terms of time
- costly for females as well - increase stress level
- male forcing female to mate with him
- male may commit infanticide
- male coersion for mating
Mating is a selfish act
- can see this in terms of cost and benefit for male/female
female costs
- injury
- disease (性病とか)
- energy (sex skin development)
- time
- predation risk
- food competitor
female benefits
- can assess male quality, can provide infant care, help protect from predator, protect from other males
Male cost
- competition with other males
- >injury
- >disease
- stress
- <-top-hormonly susceptible to disease
- <-subordinate - also have
- also, same risks of matings as females
Male Benefit
- group membership reduces predation risk
- access to females
- females give males grooming care (increase health)
- access to resources
Male-female interaction is not only mating
- male friendship
-
- defense against multi-male influxes
- female can be protected by the dominant male if she has a good relationship with him
- female-choice - prefer dominant male
- defense against multi-male influxes
Multi-male species
- female affiliation patterns
-
-
- 3 Patterns
- 1. male dominance hierarchy
- 2. promiscuous mating
- 3. Safari - have her cooperate to come with him to mate in shade
- 3 Patterns
- Macaque - diatic establish dominance hierarchy
-
female interaction
- Don't deplete sperm
- females Don't recruit male for group defense
- females don't need male to defense
- Callitrichids recruite male to increase male parental care
- inhibit infanticide
- other male can help avoid other male killing children
male-coersion
- something unusual for primate
- anthropoids phenomenon
- Catarrhines (old world monkey)
- Lemur - males are expelled
- in captured situation, he gets killed.
- dimorphism (males have)
- larger size
- huge canines
- anthropoids phenomenon
- Papio hamadryas
- males panish females
- infanticide
霊長類行動学11. オス同士の関係パターン
Primate Males
- characteristics of male behavior
- primary interest
- reproductive success
- enormous reproductive potential - skew
- only limited by female resources
- reproductive success
- benefit of long life +
- reproductive output. ie effort
- how much energy you invest
- more important
- these tow are contingent to reproductive success is relative to other males.
- (female compete for food for offspring)
- but male, only thing they care is
- one male's benefit if other male's loss
- why?
- sex ratio : 1:1
- if you mate with more than one, some males loses chance
- male sacrifice long life in order to maximize RS
male strategies is contingent with two things
- distribution of females in space and time - measure potential of competition.
- operational sex ratio - refer to old note!
- distribution and strategy of other males
- female counter strategies
- males strategies are not always accepted by females
- male strategy is divided into two
- contest (mostly) - fight against to exclude others
- scramble - deferred contest (sperm competition in promiscuity)
- if dispersed
- e.g., Gibon
- female counter strategies
- if females dispersed - males are dispersed, too.
- Polygynous mate guarding
- range v. rove
- over density period of time
- Area x #females x p(female is receptive) x p(another male mate with other female)
- low: stick to one female (e.g., Gibon)
- high: male wanders around (e.g., Orangutan)
- to maximize reproductive success
- also works for groups, too.
- range v. rove
- Gibon are rare in estrous, and female dispersed, so stick with one female.
- remember: Monogamy is only when males were forced to be from some reasons
- in Gibon's case, payoff is too high
female group size changes male's mating strategies
if mating is
- seasonal - multi-male influx
- small group of female
- within all mate band - peaceful
- end up with promiscuity mating
- aseasonal
- seek tenure
霊長類行動学10. メス同士の関係パターン
Primate Female Social Behavior
- why do females live in groups?
- What determines female group size?
- What determine the nature of female relationships with groups? between groups?
- What determines which sex disperses?
- Do females invest differently in male and female offspring?
Why do Females live in groups?
- historically, primate females were viewed as a commodity
- Partly male bias from researchers
- Partly because first species studied (Baboons) are characterized by dramatic male behavior, and subtle female behavior
- In 1960s, female primates began to receive attention
- about 80% of all diurnal primates are gregarious.
- In an evolutionary context, we need to demonstrate a benefit to individuals for belonging to a group
Why live in a group at all?
- predator defense
- Resource defense
- Mate acquisition
Predator defense
- Advantages
- "Selfish herd" effect
- predator attack one at a time, so if you are with others the probability to be attacked decreased
- alarm calls (like cebus capucinus)
- mobbing
- "Selfish herd" effect
- Disadvantages
- Predator attraction
Resource defense
- Advantages
- Access to resources
- defended by other groups
- Disadvantages
- Must share resources with your group members
What limits an individual's reproductive success?
- Females
- Time-interbirth interval
- Survival of offspring
- Males
- Access to mates
- Survival of offspring
Dichotomy of Male and Female Reproductive limitations
- Food availability limits female reproduction output
- Amount and type of food competition is what shapes the social relationships of females
- Males limited by the number of females they can inseminate
- Mate competition is more important.
In a Nutshell...
- Females are avoiding predators and pursuing food, which is their limiting resource, and males are pursuing females, which is their limiting resources.
Variation in Female-Female relationships
- Female philopatry is most common, through females disperse in some species
- Some species have well defined female hierarchies, and some don't
The Essence of the Model
- Predation risk forces females to live in groups
- Group living leads to competition for access to resources, both within and between groups
- The quantity, quality, and distribution of food should influences competition and, therefore, the types of groups that females form.
Competition
- Two basic types of competition:
- Scramble competition
- Contest competition
Scramble Competition
- Share a limited resource
- Individual can limit the access of that resource to other individuals
- Occurs when food is very dispersed.,
- Can also occur at food sources that are very large relative to the group spread.
Contest Competition
- Contest competition occurs when stronger individuals can limit the access to a resource to less powerful individuals
- Individuals differ in competitiveness
- Dominant individuals take a larger share of the resource
- Contest competition occurs when a resource occurs in well-defined patches
Resource distribution and group size
Between group competition
- Contest and Scramble competition can also occur between groups
Female perspective
-
- Where food is clumped, females tend to form groups and defend a territory
- Where food is dispersed, they may disperse
- Where food is abundant, they may form groups, but engage in scramble competition within groups
- Some females are solitary, but usually have relationship with other females
Male perspective
- If females are dispersed
- Little change for polygyny
- If females arr clumped..
- one male can control access to many females
- Higher potential polygynous systems
- e.g., Gibon - females are evenly dispersed, so males are not possible to have more than one female at a time.
- thus, pair bond
Summarized in a flow chart
Female social relationships
- Female relationships in primates are complex
- Simplify into two basic types of interactions:
- Competitive (antagonistic)
- Cooperative (affiliation)
- e.g., grooming, allomothering, and etc.
Dominance
- Liner Dominance Hierarchy
A → B → C
Competition and Evenly distributed resources
- For example, leaves
- Which groups, scramble competition dominates
- Why?
- Resources are evenly dispersed
- Females cannot use aggression to get a larger share of a resource
- Alliance won't help defend such a resource
- Why?
- Females may congregate to reduce predation risk
- Groups are small and passive
- Such relationships may be described as "egalitarian"
- (i.e., no dominance hierarchy or difficult to detect)
- Between group competition is also scramble
- Inter-group relationships tend to be peaceful. Females intermingle.
Competition and Clumped Resources
- Within groups, contest competition is important
- Aggression can be used to compete for food
- Alliances are useful, especially if you aid a closely related female (inclusive fitness)
- Female rank should affect female reproduction success
- Tendency to stay in natal group and form bonds with closely related females
- Well established dominance hierarchies are common.
- What if predation risk is low and resources are clumped?
- No need for cohesive female groups
- Between group competition can be more important
Which sex disperses?
- The costs of dispersal
- It's dangerous to disperse
- Most commonly, males disperse
- Male mortality spikes when they disperse
- Other costs are associated with dispersal
- Alliances may be important
- Given the costs of dispersal
- Females should attempt to remain philopatric...
- ...if she can reproduce successfully at home
- If not, then, she should take her chances elsewhere
- female dispersal is therefore rare and complex
Primatological Examples of these principles
Pongo
- Large-bodied and highly arboreal
- Avoid terrestrial predators (e.g., tigers in Sumatra)
- Resources are patchy
- Large body size
- Long inter-birth interval (high reproductive cost)
- Densities are low
- Female kin are scarce, may tolerate range overlap with kin
- Females inhabit isolated territories, but show friendly relationships in a dispersed social network
- They avoid each other through dispersal, but not an active avoidance mechanism.
Pan troglodytes
- Females disperse within smaller territories
- Maintain complex social relationships with other females
- They avoid each other through simple dispersal, but regularly form parties
- Party size is correlated with food availability.
- There is some tendency to dominate by some females, but ranks are not rigid, and dominance can only be expressed in broad terms.
Hylobates
- Females disperse to territories, which are defended against other females.
- Usually, contact is avoided through dueting.
- Scramble for territories, then contest
- http://www.arkive.org/siamang/symphalangus-syndactylus/video-13.html
Galago
- Females aggressively defend territories against other females
Macaca and Papio
- Often rely on foods that occur in clumps, which can be monopolized
- Contest competition both within and between groups
- Females should be philopatric
- Form alliances with kin in both within- and between-group contest competition
- Higher ranking females should have higher reproductive success than lower ranking females
- Low ranking females tend to get fewer resources
- Most obvious effect when resources are scarce
- Lose offspring first
- Most obvious effect when resources are scarce
- Low ranking females tend to get fewer resources
- Baboons and macaques from matrilineal dominance hierarchies
- Females form linear dominance hierarchies based on agonistic interactions
- Whole matrilines are dominant or subordinate to others
- Females inherit their ranks from their mothers
- Matrilines maintained by coalitionary aggression - mutual support
- Size of the coalition determines the outcome
- Females in groups tend to show a lot of reconciliation behavior
- Groom one another or show other friendly behavior
Semnopithecus setellus (Hanuman langur)
- vary in relationship to resources
- Females don't form coalitions, competition is typically scramble, with some contest
- Some female groups are characterized by age-granted hierarchies
- In this case, females establish an agonistic dominance hierarchies.
- Young females tend to be dominant over older females.
- Classic case is Semnopithecus entellus
- Some female groups are characterized by age-granted hierarchies
- In species where females transfer, young incoming females may rise quickly to the top position, then decline in rank with age.
Marmosets
- Young females are subordinate to their mothers
- Cost of dispersal is high for young female, so she stays and helps mother raise offspring
- Marmosets live in groups where adult females in same group as mother will not cycle until leave home
- Beat up daughters to prevent them from cycling
- ovulation is suppressed
Alouatta
- Highly folivorous, expectation would be scramble competition and no female hierarchies, no barriers to transfer, no formal signs of submission
- However, howler females often actively resist immigration of females from other groups. They also evict some females from their groups
- why?
- Population density and saturation of habitat
- Female competition is more intense in small groups. If you are near the carrying capacity of your habitat, you stand to lose more by admitting a new individual
- Live in fragmented forests
- Within group competition is actually high
- Infant survival correlated with maternal rank
- However, no formal signs of submission exist
- Is this a sign of howlers living in an environment that is different to the one they adapted to?
Do females invest differently in Male and Female Offspring?
- Hypothesis: low ranking females invest heavily in sons, high ranking females in daughters
- current data suggests it is not true
- Why would you preferentially invest in one sex over the other?
- Will doing so increase your genetic fitness?
- Males can have higher potential lifetime reproductive outputs
- If you are a high ranking female and raise a high ranking male, this should maximize you fitness
- Therefore, dominant females should invest in sons
- Low ranking males stand little change of reproducing; low ranking females should invest in daughters
- Daughters are also potential allies in matrilineal hierarchies.
- If you are a high ranking female and raise a high ranking male, this should maximize you fitness
Estrus Asynchrony in with Estrous Synchrony?
Lemur catta (ring-tailed lemur)
- Breed seasonally
- Seasonal synchrony of estrus
- All females in a group cycle within about a 20 day period
- However, no two females cycle on the same day. Why?
- Females are dominant to males and solicit matings
- Asynchrony may circumvent this temporal conflict with other females
- Many females can mate with the same "high quality" male.
- Seasonal synchrony of estrus
霊長類行動学9. 母子関係
The Primate Mother-Infant Bond
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..
- (Harlow's experiments)
- Mother provides energy food (milk) until weaning age
- benefit for the mother
- Infant is mother's reproductive outlet
Variation in relationships among species
- Taxonomic distinctions
- 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
- orangutans: mother is solitary with infant.
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
- Lemur catta, Colobus polykomos, Cercopithecus aethiops, Erythrocebus patas, Macaca fuscata, M. mulatta, Papio. sp., Cebus, Saimiri, Theropithecus, Alouatta, Gorilla, Pan.
- 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.
- Galagos adult female offspring will stay in or near mother's territory, effectively dividing it up, until new territory opens
- 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.
霊長類行動学8. Scramble versus contest competition
Competition
- competition - key is contestability
- seems to be driven by greed, but really driven by limitation of resources
- contest competition: fight for access to resource
- e.g., １０人に一つのパイをあげる際、一箇所に固まっておく→取り合いして勝ったものが取りたいだけ得る。
- scramble competition: rush to gain access to a share
- e.g., divide into a piece and scatter -> 早い者勝ちで取り合う。
- 動物園では餌を散らしてやることで、decrease aggression
- each condition is associated with resources (food / females)
- clumped like fruit -> contest competition
- scattered like leaves -> scramble competition
Competition in Females
manifest as within group or between group
- Availability of fruit depends on its abundance and party size in the teritorry
- females actively defend territory from other groups
Female Orangutan (Fruitgivore)
- scrabmle competition
- females are dispersed in environment
Female Chimp
- classic scramble competition
- group size is big
- usually
- eat fruit
- rainy season
- keep eating fruits, keeping scramble competition, by dispersing more.
Female Gorilla
- scramble competition
- group size is constant
- usually
- eat fruit
- Rainy season
- start eating leaves
- not compete over resources
Female Gibbons
Female Galagos
- strict territory
- classic contest competition even though they eat insects
- in some species, the style of comtetition changes correlating with the group size.
- in some species, they swith contest and scramble competition when the population gets too big in the territory
Competition in Males
- more complected
- female are the resources for male
- contest style changes depending on
- female clumped
- female dispersed
- most male engages in contest competition,
Male Brachyteles arachnoides (めちゃくちゃなやつら)
- scramble competition - another exception
- sperm compeition (sexual selection)
- polygynyandry
Male Chimp
Male Gorilla
- if limited dispersed resource (feamale)
- strong contest competition
- acquisition of territory is scramble competition
- once one decides his territory, he will be fine.
霊長類行動学7. ゲーム理論
霊長類行動学もくじ
- in order to pass genes
- eat
- survive
- reproduction
Evolutionary Stable Strategy (ESS)
進化的に安定な戦略（しんかてきにあんていなせんりゃく、ESS：evolutionarily stable strategy）は、進化生物学およびゲーム理論の重要な概念である。ジョン・メイナード＝スミスとジョージ・プライスによって1973年に提唱された（詳細はMaynard Smith, 1982）。これは、生物の母集団のとる、「侵略されない戦略」の概念を基礎としている。仮に突然変異で対立遺伝子が発生し、別の戦略を取って他の生物に働きかけようとしても、母集団を侵略することはできず、逆に自然淘汰で排除されてしまうような戦略である。
(Wikipedia)
- Developed by J. Maynard Smith (1973)
- Strategy is a programmed behavioral policy
- e.g., Attack opponent. If he flees, chase him; if he turns around and fight back, run away.
- ESS is a strategy, adopted by most members of a population, that cannot be bettered by an alternative strategy
- Once it is fixed in a population, natural selection alone is sufficient to prevent alternative strategies from taking over.
- off course environment change, behavior has to be changed
Hawk and Dove Model
- they can interact as either:
- Hawk: Fight hard; retreat only when seriously injured
- Dove: threatens but retreat to avoid injury
- so, what happens when...
- Hawk fights dove
- Dove retreats, Hawk wins
- Hawk fight hawk
- one dies or is seriously injured, the other wins
- Dove fight dove
- threaten till one tires and retreats
- Hawk fights dove
- The caveat is that neither individual knows whether the other one is a hawk or dove. the only way to find out is to fight.
- Question is that which strategy is more stable (works best)?
- To answer this question we assign mathematical values which represent potential gains and loses
| points | End result |
| 50 | win |
| 0 | loose |
| -100 | seriously injured |
| -10 | wasting time |
- wasting time for Dove is detrimental because engaging in fighting and gaining nothing, wasting time for foraging and reproduction opportunity
- e.g., bird has to catch food every 30s to feed children
Take 2 Doves
- How many points does the winner get?
- 50 - 10 = 40
- How many points does the loser get?
- 0 - 10 = -10
- Average pay-off of strategy
- On average an individual wins half the time and looses half the time
- Thus, the average spread off is the average of the payoff of the 2 strategies: +40 and -10 = 15.
- Let's throw in hawks and do the math for all scenarios
| Hawk | Dove | |
| Hawk | 50 / -100 | 50 / 0 |
| Dove | 0 / 50 | -10 /40 |
Comparing the 2 strategies
- Dove = 15
- Hawk = -25
- Then, why have hawks at all?
- The ESS is having a stable ration of doves and hawks (5:7)
- Evolutionarily speaking limited war strategies benefit individual animals as well as the species.
Example of Doves strategy
- Lemur
- stink fight: scent competition by 手をこすりあわせてくさいにおいを出す。
The retaliator
- In this strategy, the individual plays like a dove at the beginning of every fight. If his opponent attacks he retaliates.
- He acts like a hawk when faced with a hawk, and like a dove when face with a dove.
- This is another strategy, in which the behavior of the individual is based on the behavior of his opponent. He is a "conditional strategist"
Other conditional strategists
- Bully - behaves like a hawk until someone hits back. Then the bully retreats.
- Prober-retaliator - like retaliator but occasionally tries an escalation and continuous if not retaliated.
Which is the best? stable?
- Dove
- not stable because can be invaded by other
- Hawk
- could be invaded by Dove and Bully
- Retaliator
- most stable
- Bully
- Prober-retaliator
- nearly stable
→retaliator
Prisoner's Dilemma
- Introduced by Hamilton (1964) to outline how behavioral strategies get fixed in populations.
- Two suspects of are arrested for robbery
- the police does not have enough circumstantial evidence to convict of the robbery, only evidence is for trespassing. Thus, they need a confession.
- They offer incentives for a confession
- This would require the suspect to rat out his partner. What to do?
- Punishment for trespassing: 1 year in jail
- Punishment for robbery: 10 years
- Consequences of confession: Silent partner gets 10 years in jail; rat gets off with no jail time
- If both confess: 5 years in jail for both
- What to do?
| Cooperate | Defect | |
| Cooperate | -1 / -1 | -10 / 0 |
| Defect | 0 / -10 | -5 / -5 |
How often do we rat out?
- there are other variables that may influence a person's decision besides the consequences for him/herself.
- related to kin selection
TIT for TAT
- One the first move co-operate. One each succeeding move do what your opponent did the previous move. Thus, TIT FOR TAT was a strategy of co-operation based on reciprocity
- This is an ESS, that may explain the evolution of cooperation.
- 1. Never be the first to defect
- 2. Retaliate only after your partner has defected
- 3. Be prepared to forgive after carrying out just one act of retaliation
- 4. adopt this strategy only if the probability of meeting the same player again exceeds 2/3.
- Provided that the probability of future interaction between two individuals is sufficiently great, co-operation based on reciprocity can indeed get started in an a social world, can flourish and can defend itself once fully established
- examples: predator calls in vervet monkeys.
- have different calls for different predator
- Colobus monkey, Diana monkey(?), Chimp
- examples: predator calls in vervet monkeys.
Another successful strategy
- living in groups
- theory of mind
- if primate have it or not?
- if they don't have , they can predict behavior of others?
- or they just predict based on past experience
Cheaters in ESS
- Tragedy of the commons- if everyone cheats then everyone will loose
- Thus, in a ESS there is selection against cheating. Cheaters are not eliminated completely but kept to a minimum
- Examples: monkey fooling con-specifics to hog food for itself. Can you think of other ones?
- ５人ぐらし。それぞれが家事を。１人がやらなくてもそこまで問題じゃないが、みんながやらなければ・・・。
- テストで話し合いが可だった。勉強しない人も点数が取れる。みんな勉強しなければ・・・
- Examples: monkey fooling con-specifics to hog food for itself. Can you think of other ones?
review
- Game theory is important
- Dove Hoke example
- evolutionary stable behavioral strategy
- cost-benefit of behavior
- retaliator and punishes model - represent human and chimp
- retaliator - against action
- punisher - against opponent
- come back later
- moral
- thing have to be learned
- evidence: varies depending on places
- religion
- culture
- social contract
- evidence: varies depending on places
- thing have to be learned
- game theory
- used to model behavior
- not have to be actual reality
- purpose is to test ideas
- evaluate condition mathematically
- test if the behavior or strategy is stable or not
霊長類行動学6.性淘汰(Sexual Selection)
sexual selection (1871)
- no apparent survival value, but very important and very different from natural selection
性淘汰（せいとうた）または性選択とは、進化生物学における重要な理論の一つ。異性をめぐる競争を通じて起きる進化のこと。クジャクやシカのように雌雄で著しく色彩や形態・生態が異なる動物について、その進化を説明するためにチャールズ・ダーウィンが提唱した。
一つの種において、ある性（ほとんどの場合は雌）の個体数や交尾の機会はもう一方の性よりも少ない。それゆえ、交尾をめぐる個体間の争いが起き、進化を促す。本項では便宜上、メスがオスを選ぶ場合を想定して記述する。
性淘汰は通常は自然淘汰とは別のメカニズムとして論じられる。主にオスとメスの社会関係に由来する現象であること、オスとメスに異なった淘汰圧を加えることなどがその理由である。しかし広義には性淘汰は自然淘汰に含められる。ある個体にとっては他の個体の形質や好みは環境の重要な要因のひとつである。また長い尾羽のような装飾的な形質も、長さの上限が生存上の不利さによって制限されているなど、自然淘汰と全く独立して論ずることはできないからである
(Wikipedia)
- 1930's Fisher revised the model (ignored for years)
- 1. Proved mathematical viability of the model
- 2. strength of phenomenon
- showed it is powerful force of nature
- 1971 - Campbell
- Trivers - parental investment
- he revolutionised
- he solved problems of low of male and female investment in offspring.
- Trivers - parental investment
ロバート・トリヴァースは親の子育て行動を経済学の投資、利益、コストという概念を用いて説明できることを示した。親は自分の持つ有限資源（寿命、エサなど）をどのように自分の生存と子孫を残す努力へ振り分けるか常に判断を迫られている。つまり最も効率よく振り分けできた個体が繁栄する。親は獲得したエサを自分で食べるか、子に与えるか、自己の利益を最大化できる方を選ばなくてはならない。また子にとっては自分が親から与えられる子育ての労力は100%有意義であるが、50%しか遺伝子を共有していない兄妹たちへの子育てはその半分の価値しか持たない。鳥類に多く見られる「兄による弟殺し」は、兄弟間の対立であると同時に、親が予備として子を多めに産んで、第一子が上手く育ちそうなら弟を殺させるという、親子間の利害対立が原因だと考えられている。
(Wikipedia)
Differential reproductive success
- arising from patterns of mating
- 1. mate competition
- 2. mate choice
- anisogamy (異型配偶子)
- female have the largest gamete (配偶子)
- male have a smaller gamete
精子や卵子のように、有性生殖を行う生物が作る配偶子の形態が異なる配偶子のこと。
(三省堂辞書)
- larger gamate tend to need more time to be produced
- e.g.,
- female: 400,000 occytes (卵母細胞)
- 1 egg / month
- 3 eggs every 4 years
- e.g.,
Control of mating
female choice (larger gammies: control partners)
- 1. good genes - "better offspring"
- 2. good help - "better partner"
male competition (small gamate: control access to mates)
- 1. attract mates through advertisement
- 2. forcibly exclude others from access
- 3. out produce gamates
- 4. block gamete access
- カエルもメスにくっついて他に取られないようにしたり
female choice
based on
- 1. good genes
- health of male
- size and strength
- color
- symmetry
- complexion (顔色)
- genetic compatibility
- major history compatibility complex (MHC) - want to mate with different
- 2. Provisioning
- food for female
- food for offspring
- (resource defense polygyny)
- males do not directly compete over females, but resources required for females
- Emilin, ST and Oring LW (1977) Ecology, sexual selection, and the evolution of mating systems. Science 197: 215-223
- sexual selection is relatively slight in monogamous groups while it is intense in highly polygamous societies.
- many environmental factors affect the potential for control of mate resources. But primary among these are the spatial and temporal patterns of resource dispersion.
- Certain environmental factors, particularly the spatial dispersion pattern of key resources and the temporal availability of receptive mates, are important determinants of these cost and benefits.
- The greater the potential for individuals to monopolize resources or mates, the greater the intensity of sexual selection and the greater the environmental potential for polygamy.
- 3. Protection from other males
- not protection for females, but for offsprings
male competition
- contingent to availability of females
- 1. female clumping (spatial distribution)
- 2. female receptivity (temporal distribution)
- operational sex ratio (OSR) = # receptive females available per male
- contingent to group size
- spatial distribution and estrus overlap
- if all females are synchronous, male only gets 1.
- multi male group
- male forms dominance hierarchies to give "priority of access"
- single male groups
- OSR measures Potential of sexual selection, but not directly.
| group | A | B |
| ratio | 12 males:12 females | 12 males:12 females |
| estrus period | 1 female/mo | all the females at the same time |
| OSR | 12:1 | 12:12 |
| description | reproductive skew - only one get 100 % | equally distributed chance |
