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大學部 生態學與保育生物學學程 (必選)
2010 年 秋冬
團體生活，利他和合作
(Group Living, Altruism, and
Cooperation)
─動物行為學 (Ethology)
鄭先祐(Ayo)
國立 臺南大學 環境與生態學院
生態科學與技術學系 教授
Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/
Part 3. 個體間的互動
 生殖行為 (Reproductive Behavior)
 親代照顧與交配體系 (Parental Care and Mating




Systems)
溝通：管道與功能 (Communication: Channels and
Functions)
溝通的演化 (The Evolution of Communication)
衝突 (Conflict)
團體生活，利他和合作 (Group Living, Altruism,
and Cooperation)
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17 團體生活，利他和合作
 Living in Groups: from aggregation to structured
societies
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Benefits of Group living
Costs of living in groups
Balancing costs and benefits
 The puzzle of altruism
 Individual selection and altruism
 Kin selection
 Reciprocal altruism
 manipulation
 Examples of cooperation among animals
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An introduction to group living
 Ladybug beetles overwinter in aggregations of
thousands of individuals
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They crawl inside rock crevices and houses for shelter
They were introduced from Asia to control invasive
pests
Have become wildly successful and their numbers have
soared
They outcompete and even eat native ladybug species
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Animal groups: simple to complex
 Ladybug groups are at the “simpler” end of the spectrum
 No evidence that ladybugs interact in complex ways
 Other species form groups
 Individuals respond to the same features of the
environment
 The other end of the scale of animal groups:
chimpanzees
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After conflict, one chimpanzee opponent approaches the
other, offering an open hand
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Benefits of living in groups
 Societies: chimpanzees and other species are
members of structured groups
 Fitness benefits accrue to animals living in groups
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Improved foraging
Decreased risk of predation
Conservation of water and heat
Decreased energetic costs of movement
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Cooperative hunting improves foraging
 Cooperative hunting in groups improves foraging success
 Harris’s hawks live and hunt in family groups
 In early morning, family members gather at one perch site
 The group splits into smaller subgroups
 The subgroups take turns flying through their family’s area
 Hawks employ different hunting tactics
 The surprise pounce(猛撲): hawks converge(聚集) on a
rabbit
 Flush-and-ambush tactic: hawks flush the rabbit and other
family members pounce on it
 Relay (換班) attack: family members chase the prey, with a
new lead bird taking over
each time
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Cooperative hunters share prey
 For cooperative hunting to be favored by selection
 Individuals must average at least the same amount of food
they would get by hunting alone
 Hunting success must be increased in groups
 Harris's hawks
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 In Harris's hawks, larger group size increases the chance of a kill
 Even with more individuals, the energy intake per individual from prey
is higher in larger groups
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Improved foraging: information sharing
 Animals improve foraging in groups by information
sharing
 Individuals pay attention when conspecifics discover food


They use this information to guide their own foraging
Geese land nearer artificial geese with their heads down in a
feeding position than to those standing erect
 Communal roosts or colonies can act as information
centers


Successful foragers return to the roost or colony and then
return to the food site
Seen in cliff swallows and honeybees
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 cliff swallows
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Decreasing predation risk
 The many eyes hypothesis: better predator detection
 Animals in groups give alarm signals
 The dilution effect: an individual in a group has a
smaller chance of becoming the next victim
 The selfish herd hypothesis: animals in the center of
the group have a lower chance of being preyed upon
 Confusion effect: fleeing in different directions
decreases a predator’s ability to track and kill any one
individual
 Group members can band together to drive a predator
away
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Conserving heat and water
 By huddling together, animals reduce the surface area
exposed to the environment

Reducing the loss of heat or water
 Many mammals sleep or overwinter together in
communal burrows
 Many birds perch snuggled (偎依) up next to one
another

The metabolic rates of penguins is reduced compared to
isolated birds
 Even some slugs (蛞蝓) rest in contact with one
another to reduce water loss
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Conserving energy by moving together
 Drafting (riding close behind in the slipstream of
another)

Reduces the amount of energy needed to move
 Holds true for animal groups that travel together
 Schools of fish
 Flocks of birds
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 Pelicans (鵜鶘)
flying in a V
formation have
lower heart rates
than birds flying
solo
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Cost of group living: increased
competition
 Individuals that live in groups often compete with each
other For mates, nest sites, or food
 Some snails secret a mucous net that floats on water
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
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The snail draws the net in to eat the mucous and its catch
When snails group, their mucous nets overlap and stick
Snails adjust for neighbors by retracting their nets quickly
 Group-living animals might lose food to thieves
 Stealing can be considered a strategy
 There is a limit on how many “scroungers” (thieves) a
population supports before the strategy becomes
unrewarding
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Costs of group living: increased disease
and parasites
 Proximity to conspecifics presents an increased risk of
infection
 Larger colonies of cliff swallows have more bloodsucking swallow bugs
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
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Which reduce nestling mass, and decrease survival
Larger colonies have higher levels of glucocorticoid
hormones, released in response to stress
The stress response was caused by exposure to the
parasites
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Fending off(擊退) disease and parasites
 Group-living species have behaviors that help fend off
disease and parasites
 Allogrooming: animals groom each other and pick off
ectoparasites
 Social insects (honeybees, ants and termites) remove
corpses and other waste from the colony

And wall off or remove infected individuals
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Costs of group living: interference with
reproduction
 Extra-pair copulations (outside of the pair bond) are
common Even among “monogamous” birds
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
Males may take care for young that are not theirs
A female may not notice when another female deposits an
egg in her nest
 Allonursing: mammalian mothers nurse offspring not
their own
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In shared roosts, reproducing communally or in a small
space
May provide fitness benefits to the nursing mother (e.g.,
feeding related young or the mother will reciprocate later)
It may be misdirectedAyoparental
care (mistaken identity)
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Balancing costs and benefits
 Hunting success alone does not explain formation of
prides in lions

Benefits of group living include defense of food, young,
and space against conspecifics
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Costs and benefits of group living may
differ across individuals
 Whirligig beetles form aggregations on the surface of
fresh water
 Beetles at the outside edge are more likely to get food

But are also more likely to get attacked
 Beetles weigh the tradeoff between predation risk and
food availability

Depending on how hungry they are
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 Hungry beetles move to the outside of the group, in
spite of the risk
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The puzzle of altruism
 Why do some animals help other members of their
species?
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A Belding’s ground squirrel increases its risk of being
spotted by an approaching predator when it barks an alarm
Dwarf mongooses feed young of others and guard the den
Eusocial insects (ants, termites, wasps and bees) care for
their colony and rear young that are not their own
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 Wild turkey males form coalitions (聯盟) that court
females and defend(保護) them, but only dominant
males father offspring
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Altruism
 Altruistic behavior appears to be costly to the altruist
 And beneficial to another member of its species
 Altruism is defined in terms of fitness
 It is a behavior that raises the fitness (number of offspring
produced that live to breed) of another individual
 At the expense of the altruist’s direct fitness, measured by
the number of offspring it leaves
 How could altruism evolve?
 Shouldn’t alleles that promote selfish behavior multiply
more quickly than alleles that promote altruism?
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Individual selection and altruism
 Behavior may appear to benefit others at a cost to the actor
 In fact, the actor might directly benefit from its behavior
 An animal that gives an alarm call may appear to be alerting
others at is own expense

But it improves its own survival by alerting the predator that it
has been seen
 Some cichlid fish (慈鯛魚) adopt unrelated young into their
own brood

The parents gain: the adopted young reduce the predation risk
of their own young
 Before assuming that a behavior is truly altruistic
 Determine if the actor benefits
directly
from the behavior
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Kin selection
 Natural selection increases the frequency of an altruistic
trait


Individuals improve their fitness through their own offspring
(descendent kin)
And through the reproductive success of other relatives
(nondescendent kin)
 Kin selection: family members other than offspring possess
copies of some of the same alleles

Because they inherited the alleles from the same ancestor
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Kin selection duplicates alleles
 If family members increase their reproductive success
 The alleles that the altruist has in common with them are
also duplicated
 Just as if the altruist reproduced personally
 Not all relatives have the same likelihood of sharing
alleles

Closer relatives (i.e. siblings) share more alleles than
distant relatives (i.e. cousins)
 Coefficient of relatedness (r): the probability that
particular pairs of relatives share the same allele through
common descent
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The coefficient of relatedness
 There is a 50–50 chance (probability of 0.5) that any
particular allele will be found in an egg or sperm produced
by the parent

A parent and offspring have a coefficient of relatedness of 0.5
 The value of r ranges from 0 (nonrelatives) to 1 (identical
twins or clones)
 A family tree can be used to calculate the coefficient of
relatedness between more distant relatives
 An animal shares 50% of its genes with a full sibling (r = 0.5)


25% with a half sibling or grandparent (r = 0.25)
Only 12.5% with a first cousin (r = 0.125)
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Calculating relatedness (r): a family tree
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Coefficient of relatedness affects
altruism
 When will the gene for an altruistic behavior increase?
 Hamilton’s rule: B  1
C r
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B = the benefit to the recipient: extra offspring that the
relative produces because of the altruistic act

C = the cost to the actor: the number of offspring it
does not produce because of the altruistic act
r = the coefficient of relatedness between the recipient
and the actor
1/r = a value of 1 or greater (r ranges from 0-1)
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Applying Hamilton’s rule
 When should an individual forgo (放棄) reproduction
to help its sister?


For siblings, r = 0.5, so 1/r = 2
The benefits of acting altruistically must outweigh the
costs by 2:1 for an individual to help its sister reproduce
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Stop and think
 A bird would have two offspring without help
 If her altruistic sister helps her by bringing food to the
nest and driving off predators, she will have five
offspring
 This behavior has a cost to the altruist
 The altruist will not have any of her own offspring
 Whereas if she did not help, she would have one
 Will altruism be favored by natural selection?
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Expanding the definition of fitness
 Direct fitness: measured by the number of offspring
that an individual has as a result of its own efforts
 Indirect fitness: the number of extra offspring that an
individual gains by helping a relative

Devalued by the genetic distance between the
individual and the relative who was helped (in other
words, multiplied by r)
 Inclusive fitness: the sum of direct and indirect
fitness
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Discriminating between kin and non-kin
 If animals can aid each other
 It should be evolutionarily advantageous to
discriminate kin from non-kin
 Animals discriminate kin versus non-kin in four ways
 Location
 Familiarity
 Phenotype matching
 Recognition alleles
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Kin vs. non-kin: location
 Individual animals are often found in predictable
locations
 In mammals males generally disperse from home

Females tend to remain in their natal area
 Female mammals that help conspecifics located near
their home are likely to be helping relatives


Even if they do not recognize them individually as kin
They follow the rule of thumb “if you are a female, help
those near home” which leads to increased inclusive
fitness
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Location as a mechanism for kin-biased
behavior
 When a parent identifies its offspring as those young
in its nest or burrow
 Parent birds feed any young in their nest



When the young leave the nest
The parent learns to recognize its young by its calls
And rejects foreign young entering the nest
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 A bank swallow feeds any chicks inside its nest,
but ignores its own chicks if they are moved to a
nearby nest hole
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Kin vs. non-kin: familiarity
 Young learn to recognize the individuals they are raised
with, through their experiences during early development

Later, they treat familiar and unfamiliar animals differently
 A young spiny mouse uses familiarity to distinguish its
siblings
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
Weanling pups huddle(聚在一起) in pairs
And members of the pair are siblings
 Non-kin encountered during the learning process may be
mistakenly classified as kin
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Kin vs. non-kin: phenotype matching
 Animals identify kin, even if they have never met
 Through physical, behavioral, and physiological
appearances
 One’s genetic inheritance has much to do with appearance
 Family members often resemble one another
 Animals can learn the “kin phenotype”
 By learning about the phenotype of familiar individuals
 Or by learning their own phenotype
 This template is then compared against strangers
 “He looks like my brother” or “He looks like me”
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Learning the phenotype of familiar individuals
 Developing a template
 And then matching new individuals to that template
 Belding’s ground squirrels use both familiarity and
phenotype matching


Pups identify their siblings because they learn one
another’s odors while still in the same nest burrow
Juveniles and adults use phenotype matching to
discriminate relatedness among individuals they have
never encountered before
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Paper wasps identify kin from non-kin
 By using the odor of hydrocarbons in the insect’s
cuticle (skin)

The odor comes from the nest
 When a wasp meets a nestmate away from the nest
 It can recognize it
 Since a colony consists of a queen and her worker
daughters

The nest odor is a reliable label of colony members as
relatives
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 Paper wasps
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An animal can use its own phenotype as
a template
 Against which to compare strangers
 The “armpit (腋窩) effect:” imagine an individual
sniffing (嗅聞) its own armpit

And then that of a stranger
 Golden hamsters discriminate between odors of
unfamiliar kin and unfamiliar non-kin

Using their own odor to form a template
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Kin vs. non-kin: recognition alleles
 This mechanism of kin discrimination is genetically based
 The allele endows its bearer with a recognizable label
 It enables the bearer to perceive that label in others
 The bearer behaves preferentially toward others with the
label
 This recognition system is called the “green beard effect”
 The label could be any conspicuous trait (i.e. a green beard)
 As long as the allele responsible for it also causes its owner
to behave appropriately to other labeled individuals
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A green beard allele in the red fire ant
 Kin discrimination in fire ants is closely tied to genetics
 Memory (formation of a template) also plays a role
 The protein-encoding gene, Gp-9, controls social
organization (The gene has two alleles, B and b)
 Workers encountering individuals with the b allele form a
template
 Workers that come into contact with ants that bear b alleles
when forming their template

Accept only b-bearing queens (bb and Bb)
 Workers in colonies with BB individuals accept only BB
queens
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 fire ants
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Genetically-based recognition mechanisms
 Used to recognize a protein coded by a region of the
DNA

The major histocompatibility complex (MHC)
 The MHC region codes for molecules that allow the
body to distinguish between “self” and “nonself”
 These genes may serve as direct cues of relatedness

Allowing individuals to identify their kin
 Sea squirt (海鞘) larvae use MHC to discriminate kin


Groups of siblings that share an allele in the MHC region
Clump together when they settle on the sea bottom
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 Bluebell tunicates (Sea squirt) (海鞘)
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MHC plays a role in kin recognition
 Especially in the context of mate choice and incest
avoidance

In amphibians and mammals (including humans)
 There is no evidence that MHC genes influence the
perception of odor


Necessary for MHC to be a “recognition allele”
But the MHC system remains an interesting case of a
close link between genes and kin recognition
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Reciprocal altruism
 Helping relatives is favored by natural selection
 When the inclusive fitness of the helper is increased
 Natural selection also favors reciprocal altruism
 Altruism between nonrelatives
 Evolves if there is an opportunity for payback in the future
 “You scratch my back and I’ll scratch yours”
 The Prisoner’s Dilemma: in reciprocal altruism
 The costs and benefits to the altruist depend on
 Whether the recipient returns the favor
 Evolutionary game theory can handle situations such as this
 The best course of action depends on what others are doing
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The Prisoner’s Dilemma
 An imaginary story: two suspects are arrested for a crime
 Kept in separate cells to prevent them from communicating
 One of them is guilty
 But sufficient evidence is lacking for a conviction
 The prosecutor offers each a deal
 Each prisoner is told that there is enough evidence
 To guarantee a short jail term
 Freedom can be obtained by providing evidence to send the
other to jail for a long time
 If each informs on the other, they both go to jail for an
intermediate length of time
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Constructing a payoff matrix
 The strategies available to each player are:
 To cooperate (don’t squeal on your partner)
 To defect (squeal)
 The best strategy: defect while your partner cooperates
 Payoff = T (the temptation to defect)
 If both you and your partner cooperate the payoff is R
(reward)
 If both partners defect, the payoff is P (punishment)
 If you cooperate and your partner defects

You get the lowest possible payoff, S (for sucker’s payoff)
 The payoffs must be in the order T > R > P > S
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The best strategy for Prisoner’s Dilemma
 Examine the payoff matrix
 Player 1: the best strategy if the opponent cooperates?
 Because T > R, it is better to defect—you will go free
 Similarly, if the opponent squeals
 Because P > S
 It is better to defect, rather than taking the rap
 In a single round of the game, it is always better to defect
 This is a “dilemma”
 If both players follow this logic, they will both defect, and
will both do worse than if they both cooperated
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Tit for tat (一報還一報)
 The Prisoner’s Dilemma implies that reciprocal altruism
cannot evolve


If the prisoners never meet again
But individuals do interact, so reciprocal altruism may evolve
 The “tit-for-tat” strategy: repeated games of Prisoner’s
Dilemma
 An individual begins by being cooperative



In all other interactions: match the other party’s previous
action Be “nice” (begin with cooperation)
Retaliate immediately (if the partner defects, defect in return)
Forgive immediately (“forget” a defection and cooperate if the
partner later cooperates) Ayo 教材 (動物行為學 2010)
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Reciprocal altruism can be an ESS
 If a population of individuals adopts this strategy
 It cannot be overrun by a selfish mutant that always
defects
 When individuals have repeated encounters
 Reciprocal altruism can be an evolutionarily stable
strategy (ESS)
 Cannot be invaded by another strategy
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When reciprocal altruism is likely to
evolve
 Conditions that favor reciprocal altruism:
 The benefit of the act to the recipient is greater than the
cost to the actor
 The opportunity for repayment is likely to occur
 The altruist and the recipient are able to recognize each
other
 These factors occur in a highly social species
 With a good memory
 Long life span
 Low dispersal rate
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Reciprocal altruism in vampire bats
 Vampire bats bite large mammals and lap up the blood
 Consuming up to 50% of their body mass
 A bat that did not obtain a blood meal begs for food
 A receptive donor regurgitates blood
 Regurgitated food sustains the hungry bat until the next
night
 When it may find its own meal
 Donors give blood to recipients that are not related to
them
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Vampire bats evolved reciprocal altruism
 The benefit to the recipient of the blood gift exceeds the
cost to the donor


The recipient gains 12 hours of life and a chance to find food
The donor has two nights of hunting before it would starve
 Bats have the opportunity to repay favors and get favors
repaid


Most bats will need blood at some time
They will encounter the same individuals again
 Individuals recognize each other
 Only bats who have had a prior association share food
 Pairs of unrelated bats regurgitated almost exclusively to
each other
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Manipulation
 Animals can coerce (迫使) others to help them

Particularly between parents and offspring
 Because parents and offspring are not genetically identical
 Their interests are not always perfectly aligned
 Parents have an advantage in power struggles
 They are larger and more experienced than their offspring
 Because offspring are related to their parents
 Their motivation to resist(反抗) coercion is reduced
 If offspring forgo(放棄) their own breeding to help their
parents reproduce

They at least gain indirect fitness
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Cooperation among animals: alarm calls
 When Belding’s ground squirrels spot a ground
predator (badgers, snakes, coyotes)

Their alarm call is a series of short sounds
 When they spot an aerial predator (hawks and eagles)
 Their call is a high-pitched whistle
 Are these calls directed at the predator to let it know it
has been detected?

Or are they directed at kin?
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Individual selection in Belding’s ground
squirrels
 Individual selection is behind aerial predator alarm calls
 When an alarm whistle is heard, pandemonium breaks out
 Others also whistle an alarm and all scurry(急趕) to shelter
 When a hawk is successful, the victim is usually a noncaller
 The most frequent callers were in exposed positions close to
the hawk
 The alarm whistles directly benefit the caller
 By increasing its chances of escaping predation in the
ensuing chaos (接踵而來的混亂)
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Kin selection in Belding’s ground
squirrels
 Individual selection is not behind the squirrels’ alarm trills
 Given in response to terrestrial predators
 In this case, the caller is assuming a risk
 More callers than noncallers are attacked
 Predators did not give up when an alarm call was sounded
 The caller was not manipulating its neighbors to its
advantage


Other squirrels sat up and looked at the predator
Their reaction did not create chaos that might confuse a
predator
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Female Belding’s ground squirrels are
genetically related
 Squirrels practice nepotism (任人唯親): favoritism for
family members
 Females are more likely to sound an alarm with a
ground
 This is consistent with kinship theory



Females have nearby relatives that benefit from the
warning
Reproductive females are more likely to call
Reproductive females with living relatives call more
frequently
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 Expected and observed
frequencies of alarm
calls by Belding’s
ground squirrels in
response to aerial and
terrestrial predators.
 Expected frequencies
are those that would be
predicted if the
animals called
randomly. The calls in
response to aerial
predators are close to
the expected
frequencies.
 However, the calls in
response to terrestrial
predators are more
likely to be given by
females with relatives
nearby.
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Evolution of alarm calls in rodents
 Alarm calling increases the caller’s own chance of survival
 Aids the caller’s offspring (i.e. Yellow-bellied marmots)
 Or aids other animals
 Social species are more likely to call than non-social species
 Diurnal (day active) species are more likely to call
 Evolution of diurnality precedes evolution of alarm calling
 In rodent species, alarm calling communicates with predators
 Benefits arising from kin selection are secondary
 Belding’s ground squirrels benefit from kin selection
 They live in high-density meadows near relatives
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Cooperation in animals: acquiring a mate
 Males of some species cooperate in attracting a mate
 Some even relinquish (放棄) the opportunity to pass their
alleles into future generations
 At least temporarily
 These males concentrate their efforts on making another
male more attractive to females


Seems to lower fitness
But in some cases it can be advantageous
 Sometimes the benefits to cooperators can arise separately
or in combination with each other

Individual selection, kin selection, or reciprocal altruism
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Cooperation among wild turkeys
 Most male wild turkeys in some Texas populations never
mate
 A young male and his brothers form a sibling group



Will be an inseparable unit until death
Only the dominant male in each group mates
Each male’s status is decided by the outcome of two contests
 Competition for dominance within the sibling group
 Endurance is the key to success: the last one able to fight is
the winner
 Competition between rival sibling groups
 The groups fight until a dominance hierarchy is established
 The sibling group with the
most
members
is victorious
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(動物行為學
2010)
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Kin selection in wild turkeys
 Dominance hierarchies are stable: renegotiation of rank is rare
 When the breeding season begins, females visit meadows
 The brothers strut (高視闊步) in unison (和諧一致)
 Even though only the dominant male in the highest-ranking
sibling group will mate
 Kin selection: the major driving force behind this behavior
 A subordinate male gains inclusive fitness by helping his brother
perpetuate his alleles
 Without his assistance, the brother could not be successful
 Siblings must cooperate for their unit to become dominant
 Sibling strutting makes the dominant male more attractive
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Cooperation among lions
 Male lions cooperate in acquiring
mates


Form coalitions (partnerships) to
challenge males of other prides
The larger coalition usually wins
 The reward is a harem of lionesses
 Females enter reproductive condition
simultaneously


Any of the males in the coalition may
be the first to mate
A female may change mates
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Coalitions drive
out resident males
and can involve
fighting
71
Why do male lions form coalitions?
 Does kin selection underlie formation of coalitions?
 Coalitions usually consist of close relatives
 A male gains reproductive success indirectly by helping
his male relatives mate with the female
 However, kin selection is not the entire story
 Because male coalitions contain unrelated males
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 Reciprocal altruism is not important: lions attack a
stuffed lion regardless of the behavior of other lions
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Coalition size affects reproductive success
 Male lions in larger coalitions have greater reproductive
success
 A solitary male has little chance of reproducing

And much to gain by joining a coalition
 By accepting an unrelated male, a small coalition may
take over a pride
 The lifetime success of a male lion increases by
cooperating with other males

Even if all the males are not related
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 Males in larger coalitions have greater reproductive
success.
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Cooperation among long-tailed manakins
 Two or three males of this small bird species work together
 They call and perform visual displays to attract a mate
 In the up-down jump display: perching males take turns
jumping up and down
 In the cartwheel display: one male jumps upward and
backward over the second male

Which then jumps up and over the first male
 One male leaves and the remaining male
does a solo performance

The female mates with him
 The same male always mates
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Why does a subordinate manakin stay?
 It is not indirect fitness
Because the two males are probably not related
A subordinate’ chance of mating is not increased by deserting
 Solitary males cannot perform the courtship dance or mate
A subordinate male that outlives his partner obtains a subordinate
partner
 Then it will be his turn to mate and raise his direct fitness
Also, singing (which impresses females) improves with age and
practice
The most likely reason for cooperative courtship in this species?
 Increased chances of obtaining future direct fitness benefits





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Cooperation among olive baboons
 A male olive baboons enlists the help of a friend for a
female




Male A associates (consorts) with an estrous female
Male B (with no female) covets (垂涎) this female
Male B solicits the help of male C to challenge male A
While the battle is in progress, male B mates
 Male C risked injury while assisting another to acquire a
mate

Reciprocal altruism: at some time in the future, he will
enlist the help of male B to obtain his own female
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 An alliance between two male olive baboons. The
two males on the right are cooperating to challenge
the male on the left. At a later time, the male that
was assisted will have to reciprocate to maintain the
alliance.
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Cooperative breeding
 Nonbreeding helpers can reproduce
 But stay to help their parents raise young
 Acorn woodpeckers fit the definition of cooperative
breeding:


Some individuals (helpers) assist in the care and rearing of
another’s young
Rather than producing offspring of their own
 Cooperative breeding it is quite rare
 Occurs in birds, mammals, insects and spiders
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 Acorn woodpeckers live in family groups
containing nonbreeding helpers
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Helpers provide food
 Helpers pitch in to feed offspring
 Anybody, not just parents, can collect and carry food
 Reduces the parents’ job and increases health and survival
 Mammalian mothers provide milk to their offspring
 Helpers deliver food by carrying it in their jaws or stomachs
 Feeding the mother allows her more time to remain with the
pups instead of hunting
 Blackbacked jackals (黑背胡狼)
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Blackbacked jackals (黑背胡狼)
regurgitate food to pups and
mothers
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Helpers protect young and do other jobs
 Helpers provide extra protection for the young
 Florida scrub jays give alarm calls and mob predators
 Jackal families with helpers always have an adult on guard
 In fish, helpers protect but don’t feed offspring
 In some bird species, helpers may build and clean nests
 Or incubate and brood the nestlings
 Male helper saddle-backed tamarins (a small primate)
carry offspring

Mothers can obtain nourishment for herself and for an
adequate milk supply
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Is “helping” really helpful?
 In many species, the number of helpers correlates with the
survival of the young, the survival of the breeders, or both
 Helpers have no effect on the number of eggs laid

But increases the chance that the young hatch, leave the
nest, and become independent birds
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Breeding success for Florida scrub jay pairs with helpers
exceeds that of pairs without helpers
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Do helpers increase breeding success?
 Another factor, such as territory quality, may cause an
increase in the number of helpers and breeding success
 Removing helpers reduces reproductive success

Gray-crowned babbler nests where helpers were removed
raised fewer young
 Superb fairy-wren helpers did not increase offspring
survival

But increased future survival of breeding females
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Meerkat (狐獴) pups gained more weight when the number of
pups was reduced but the number of helpers remained the same
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Do breeders always
want help?
 Not always
 Helpers might compete for resources
 Or increase the chance that the mate has an extra-pair
copulation
 In pied kingfishers, helpers are tolerated only when their
services are needed


Primary helpers are older offspring
Secondary helpers, which are unrelated, are permitted to
stay when the additional fish they provide are needed
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Is it costly to help?
 Helping behavior has a cost
 Mongoose (貓鼬) helpers forgo feeding and stay at the
burrow to baby-sit and guard pups from predators


While the parents and others forage
They lose weight
 Helping may even reduce survival
 Helpers among stripe-backed wrens that bring the most
food die more quickly than other birds
 If it costly to help, why do it?
 (1) Why would an offspring delay dispersal?
 (2) Why would it help?
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 Mongoose (貓鼬)
 stripe-backed wrens
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Stop and think:
 Imagine you are spending your graduate school years
studying helping behavior in a little-known bird species

You find that birds that remain behind on their natal
territory to help their parents are far more likely to die
than those that go off to breed on their own
 In your dissertation defense, you would like to make the
argument that helping is costly


How confident are you?
What experiment(s) would you like to perform in order to
increase your confidence?
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Why should an offspring delay dispersal?
 Animals disperse to avoid inbreeding
 Or because of reproductive suppression by their relatives
 Or because of competition
 Animals exhibit philopatry because they are
 Adapted to the local conditions
 And familiar with the physical and social settings of home
 Dispersal is risky
 Small cichlid fish are eaten by predators when they disperse
 But, other options may be limited
 All available territories might be full
 Or all the available mates might be taken
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Delayed dispersal: habitat saturation
 Florida scrub jays live in limited scrub habitat
 Every territory is filled
 A male acquires a territory by
 Inheriting a portion of his parents’ property
 Replacing his father after his death
 Subdivision of his father’s territory
 Defeating a breeder
 Successfully competing for territory of a breeder that has died
 If there is more than one son helping, the dominant one wins
 So, scrub jays help their parents because they are making the
best of a bad set of circumstances
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Territory availability and quality
influences helping
 When no territories are available, juvenile acorn
woodpeckers

Remain at home and become helpers
 Not all territories are equal in quality
 It might be better to stay home if the only other
choice is a poor-quality territory
 Some Seychelle’s warblers stay to help their
parents rather than move to low-quality territories
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Delayed dispersal: lack of mates
 Mates can also be a limited resource
 Splendid fairy-wren females suffer much greater annual
mortality than do males
 Females are often in short supply
 Helpers tend to be males waiting for an available mate
 The wait can be as long as five years
 When females are scarce, male helpers are plentiful
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Why should a helper help?
 Even if an animal does not have the opportunity to breed
 That does not automatically mean it will become a helper
 Many animals become “floaters” and wander around
without a territory
 Even if an individual remains on its own territory
 It may not help
 There are other reasons beside lack of other
opportunities that underlie helping behavior


Helpers may get indirect fitness benefits
Helpers may get direct fitness benefits
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Helpers get indirect fitness benefits
 A helper benefits by increasing the production of relatives
 Older offspring help their parents raise siblings
 Kin selection can be important
 Helping in white-fronted bee-eaters did not provide direct
benefits to the helpers (increased survival or chance of
mating, and increased success in rearing young)
 But helping led to increased production of related young
 Pied kingfisher become secondary helpers when both their
parents are dead
 Long-tailed tit helpers are failed breeders that help relatives
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 white-fronted bee-eaters
 Pied kingfisher
 Long-tailed tit
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Helpers get direct fitness benefits
 A helper’s own lifetime reproductive success is increased
by its actions

Many groups have unrelated members
 Seychelle’s warblers help raise additional offspring
 Extra-pair copulation is common, so a helper may not have
the same father as the offspring it helps
 Eggs may be deposited by other birds
 Indirect benefits are lower in this species
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On the left is a nest built by a 4-year-old female Seychelles
warbler with no experience.
On the right is a nest built by a 4-year-old female that had
experience in being a helper.
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Direct fitness benefits for helpers
 They may add their own eggs to a nest
 They may be able to take over a territory budded off
from the main territory
 They have a chance to practice their parenting skills
 They may mate with the original breeder later on


Or if the original mate dies
In pied kingfishers, secondary helpers (unrelated to the
breeders) mate with the female they had previously
assisted
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Stop and think
 Helping behavior in humans has been studied from an
evolutionary perspective
 Because human children are very dependent for years


And mothers can give birth to children in rapid succession
Most mothers require help from others
 In a review of studies across many cultures
 The presence of maternal grandmothers (the mother’s
mother) and sibling helpers improves child survival
 Fathers improved child survival in only 1/3 of the studies
 What a hypothesis based on kin selection might explain
this?
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Bees are a eusocial (“truly social”) species
 Young worker honeybees feed the queen’s larval offspring
 Other workers maintain the hive and carry out the dead
 Older workers forage at flowers and communicate their location
to their hive mates in an elaborate dance
 All workers are female
 Only one individual in the hive - a queen - lays eggs
 Eusocial species are defined by three characteristics
 Reproductive division of labor
 Cooperation in the care of young
 At least two generations share in the colony’s labor
 These characteristics also apply to some cooperative breeders
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A eusociality continuum
 How evenly is reproduction is shared among group
members?


At one end, all or many of the group members breed
At the other end, breeding is restricted to one or several
group members
 Reproductive skew: describes the degree of eusociality
 The proportion of individuals that give up reproduction
 Eusociality is rare
 Occurs in ants, bees, wasps, termites, aphids, an
ambrosia beetle, thrips, spiders and snapping shrimp
 Eusociality is extremely rare in mammals
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Eusociality and cooperative breeding
Predicted locations of cooperatively breeding species along the
eusociality continuum
•
When reproduction is restricted to a single individual
– Reproductive skew = 1
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Naked mole rats are eusocial
 Breeding is restricted to a single female - the queen
 Other adult females are smaller and don’t ovulate or breed
 Colonies contain overlapping generations of offspring
 Which are communally cared for
 Duties of nonbreeder members depend on their size and
age



Smaller member gather food and transport nest material
Larger members clear the tunnels of obstructions
The largest members dig tunnels and defend the colony
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 A queen naked mole rat, the only reproductive female
of the colony, is resting on the workers that feed her
and help care for the young.
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Eusociality presents an obvious puzzle
 Members of eusocial species may relinquish all chances
of reproduction
 Eusocial colonies can be described as “superorganisms”

Members function efficiently together to ensure survival
and reproductive success of the colony
 The most common feature of eusocial societies
 They are family groups
 What favors the evolution of eusociality?
 How do eusocial colonies function on a day-to-day basis?
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Evolutionary origins of eusociality:
haplodiploidy
 Haplodiploidy: an unusual genetic system in eusocial
species


The females are diploid, with two sets of chromosomes
The males are haploid, with a single set of chromosomes
 Males grow from an unfertilized egg
 And produce sperm that are genetically identical to
themselves
 When a male mates with a female
 The female offspring get a sampling of 50% of their
mother’s DNA
 But all of the father’s DNA
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Haploidiploidy changes coefficients of
relatedness in a family
 Full sisters (share both a mother and a father) get half of
their DNA from their mothers

They share 50% of their maternally derived DNA
 Full sisters also get half their DNA from their fathers
 Because fathers are haploid and all sperm are identical
 This DNA is identical for every sister
 With the paternally and maternally derived DNA
combined

Full sisters share 75% of their DNA with one another (r =
0.75)
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 The genetic
Ayo 教材 (動物行為學 2010)
contributions of
a male and
female of a
haplodiploid
species to their
offspring.
 Males are
haploid and
have only one
set of
chromosomes.
They arise from
unfertilized eggs.
 A female of a
haplodiploid
species shares
more DNA with
her full sister
113
The relationship between haplodiploidy
and eusociality
 Haplodiploidy is not necessary for the evolution of
eusociality

Many eusocial species, such as termites, are not
haplodiploid
 Haplodiploidy alone is not sufficient for the evolution of
eusociality

There are many haplodiploid species that are not eusocial
 Even in haplodiploid species that are eusocial
 Females very often mate with more than one male
 Multiple mating reduces the relatedness among sisters
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Summary
 Benefits of group living: increased foraging success, decreased
predation risk, conservation of heat, water and energy
 Costs: competition, disease, parasites, reproductive interference
 Altruism: performance of a service benefiting a conspecific at a
cost to the one that does the deed - it is measured in units of
fitness
 Hypotheses for the evolution of altruism:
 Individual selection: an individual receives direct benefits
 Kin selection: indirect fitness increases by helping kin
 Reciprocal altruism: the altruist’s final gain exceeds its cost
 Manipulation: animals can coerce others into helping them
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Summary
 Relatives are identified through location, familiarity, phenotype




matching, and genetics
Reciprocal altruism occurs when: a recipient’s benefits exceeds
the actor’s costs, future repayment arises, individuals recognize
one another
Cooperation in acquiring a mate: through displays, coalitions or
alliances
Cooperative breeding: altruism where a helper helps rear
offspring not its own
Eusocial species: an extreme example of cooperative breeding
 Division of labor, cooperation in caring for young,
generational overlap in colony care
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Summary
 Haplodiploid sisters are more related to each other than
to their mothers or daughters

By Hamilton’s Rule, kin selection is more likely to evolve
 Factors favoring evolution of eusociality: extended
parental care, long-lasting sibling associations, sharing a
central resource
 Eusocial individuals favor colony-mates that are more
closely related
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問題與討論
[email protected]
 Ayo 台南 NUTN 站
http://myweb.nutn.edu.tw/~hycheng/
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