Slajd 1

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13. Altruism and sociality
Primitive animals are all the same. There is no
individualistic behaviour. Higher animals evolved
individualism. The highest birds and mammals
evolved individualistic characters (moods),
motions and fears.
Classical population genetic does not predict
individualism because it focuses on optimisation
and equilibrium states that are the same for all
members of a population.

• Evolutionary theory has to explain
• Altruism (the help of others despite of own
  costs)
• Cooperation of related and unrelated individuals
• The evolution of cheating
• Sexual selection (the existence of differentiated
  sexual behaviour and mating rituals)
• Biased sex ratios (the prevalence of either males
  or females in a population)
• The existence of highly altruistic insect
  societies (eusociality)
• The existence of infanticide in many mammals and
  birds
• The existence of homosexuality in many mammals
  and birds
• The appearance of common beliefs and religion in
  man

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The unit of selection and evolution
Unicellular organisms
Multicellular organisms
Higher taxonomic level
Classical population genetics (Fisher, Haldane,
Sewall Wright)
Species
Population
Wynne Edwards (1962)to explain cooperation
Higher taxonomic level
Group
Species
Family
Individual
Population
A more liberal view sees any trait inducing
carrier of information as a potential unit of
evolution. These include genes, individuals, and
even groups but not species.
Cell
Organelle
Genome
The basic unit is the gene as the smallest
essential carrier of information
Gene
C. Richard Dawkins (1941-
Nucleotid
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The game theory approach
The classical hawk and dove game

• Assume two players
• a hawk that will always fight until injured or
  until the opponent retreats
• a dove that will always retreat.
• Contests are associated will potential benefits
  (B) and potential costs (C).

John F. Nash (1928-
John Maynard Smith (1920-2004)
Hawk v. Hawk Each contest has a 50 chance to
win. The net gain is the difference between
benefits and costs of the contest
Hawk v. Dove The hawk will always win
The pay-off matrix
Hawk
Dove
½(B-C)
B
Hawk
0
½B
Dove
Dove v. Dove Each contest has a 50 chance to
win. There are no costs
Dove v. Hawk The dove will always loose
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The idea behind game theory is now to define
equilibrium conditions that define which game
(strategy behavioural phenotype) will have the
highest payoff in the long run. Maynard Smith
defined such equilibria that cannot be beaten by
other strategies as evolutionary stable
strategies (ESS). Populations of individuals
playing an ESS cannot be invaded by immigrating
individuals or by mutants playing other
strategies.
The pay-off matrix
Hawk
Dove
½(B-C)
B
Hawk
0
½B
Dove
The fitness
Is H an ESS?
If B gt C, H is always an ESS because per
definition 0 p 1.
Is D an ESS?
For H to be an ESS W(H) gt W(D) For D to be an ESS
W(D) gt W(H)
If B gt C, D is never an ESS
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The pay-off matrix
What is if costs are higher than benefits C gt B?
Hawk
Dove
At equilibrium we have
½(B-C)
B
Hawk
For C gt B an ESS is to play hawk with probability
p and dove with probability 1-p.
0
½B
Dove
Even simple games favour mixed strategies. This
is the start of individualistic behaviour.
The Retaliator game(fight when meeting a hawk
and retreat when meeting a dove)
The Bourgeois game(fight when owner, retreat
when intruder)
Hawk
Dove
Retaliator
Hawk
Dove
Bourgeois
½(B-C)
B
Hawk
½(B-C)
½(B-C)
B
Hawk
¾B-¼C
0
½B
Dove
½B-e
0
½B
Dove
¼B
½(B-C)
½Bd
Retaliator
½B-¼Cg
¼(B-C)
¾B
Bourgeois
½B
The Bourgeois is the only ESS of this game.
Retaliator and a mixed strategy are the two ESS
of this game. Realization depends on the initial
frequencies of players.
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Local mate competition
In 1967 W. D. Hamilton proposes that in the long
run organisms should preferentially invested in
the cheaper sex. The cheaper sex is the one that
promises more offspring at equal costs.
p probability to produce a son r expected
reproductive success, C cost of reproduction
Which sex to produce?
The probability that a son reproduces is high
The probability that a daughter reproduces is low

• For a proper choice a female
• needs knowledge about the actual sex ratio and
• must have the ability to control which sex she
  produces

Many Hymenoptera and some other insects have
these abilities Mammals and birds perform
selective infanticide
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Two examples of sex ratio allocation
Figs and fig wasps
Parasitic wasps
Agaonidae are closely connected to figs.
Depositing eggs into the ovaries they pollinate
figs. Males are wingless and mate only with the
local clutch
Secondary parasitism of the parasitoid wasp
Nasonia vitripennis parasitoid of blow and flesh
flies
Sex ratio is defined as the proportion of males
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Selective infanticide in man
The sex ratio is the proportion of males SR
males / (males females) The normal cross
cultural sex ratio at birth is 105 males to 100
females 0.512 (range 101 to 107 100)
Some reported sex ratios in childhood of
preindustrial societies Inuit Eskimos
0.67 Yanomamö Indians 0.56 Cashinahua, Peru
0.60 Rajput caste, India gt 0.9 Upper class
medieval Florence 0.57

• Selective infanticide in man is found in nearly
  all cultures.
• Often it serves to
• stabilize population size
• to adjust sex ratios to marriage probabilities in
  cases of highly unequal reproductive success
• to adjust to a culturally preferred gender
  (frequently the male gender)

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Reciprocal altruism
Reciprocal altruism beween non-related
individuals needs
Blood sharing in the vampire bat

• Long term association of group members.
• Donorship can be predicted from past helping.
• Roles of donors and recipients reverse.
• Benefits of the recipients outweigh donor costs.
• Donors can detect cheaters.

Exponential vampire bat weight loss function due
to starvation

• Primary social groups contain 8 to 12 adults with
  depending young.
• 30 of the blood sharing events involve adults
  feeding young other than their own.
• Blood sharing intensity depends on the degree of
  relatedness.
• Blood sharing is often reciprocal.
• Cheaters have not been observed.

Weight lost
Donor
Recipient
Weight gained
Time lost
Time gained
Benefits outweigh costs
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Cooperative breeding and helpers at the nest
In the pied kingfisher Ceryle rudis primary and
secondary helpers at the nest occur.
Helpers occur in many higher bird species and
help adults to raise the offspring.
Primary helpers are older sons that are yet
unable to breed. They increase their fitness via
their younger sisters and due to additional
experience. Secondary helping males are
unrelated to the pair they help. Secondary
helpers increase their fitness due to the chance
to become the widows mate if the breeding male
dies.
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The evolution of cheating or the Prisoners
dilemma
Assume two prisoners have the alternative either
of defect the other or to cooperate. Defection
means shorter imprisoning.
The pay-off matrix
BgtC If both prisoners defect they do worse than
if both cooperate. However cheating the other is
superior irrespective of what the other makes.
Hence pure cooperation can never evolve.
Defect
Cooperate
Defect
0
0
B(A)
0
Cooperate
0
B(B)
C(A)
C(B)
Now assume an iterative game where the players
play many times. What would be the best strategy?
In the long run there are several possible
strategies
The prisoners dilemma cannot fully be resolved
analytically. The first software solution was
provided by Rapoport in 1980.
One EES is Tit for Tat (defect if prior being
defected and cooperate if the other prior also
cooperated).
Defect
Cooperate
Tit for Tat
The program playedTit for Tat or reciprocal
altruism. The other EES of this game is always
defect.
0
e
Defect
0
-d
g
Cooperate
g
0
g
Tit for Tat
g
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Inbreeding
What is the probability for a children to get a
certain allele from their grandparents?
GM1
GF1
GF2
Grandparents
GM1
GF1
GF1
GM2
GM2
A,B
C,D
G,H
E,F
A,B
C,D
C,D
E,F
Parents
M
F
M
F
P(C)0.25
P(C)0.25
P(C)0.25
P(C)0
Ch
Ch
P(C)0.125
P(C)0.25
Childrens
The probability that Ch gets allele C is 0.125.
The probability that Ch gets allele C is 0.25.
GF1 is already inbred
The mean probability to get an allele X from one
of the members of a lineage is called the
coefficient of inbreeding.
GM1
GF1
GF1
GM2
A,B
C,C
E,F
C,C
Sewall Wright defined this coefficient as
M
F
P(C)0.5
P(C)0.5
Ch
P(C)0.5
The probability that Ch gets allele C is 0.5.
rl?m is the path from l to descendent m and L the
length of path i.
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Inclusive fitness
In the Hawk - Dove game the EES for C gt B
was BltpC ? pBgtC P was the probability of a
trait to occur. This is formally identical with
the probability of a gene to occur via descent,
it is identical to the coefficient of inbreeding.
William D. Hamilton (1936-2000)
Hamiltons rule of inclusive fitness
A simple example
Assume a new gene A that promotes parental care.
The probability of transmitting A from mother to
daughter is 0.5. Even if the mother would die
due to parental care (cost 1) two additional
raised offspring (B 2) satisfy Hamiltons
rule. 0.5 1 / 2 Parental care should therefore
be widespread in animals.
In cockroaches (Phoraspis and Thorax) the young
bite wholes in the mothers thorax to feed from
their haemolymph.
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Kin selection and the evolution of sociality
Members cooperate but retain reproductive ability
Part of the members loose own reproductivity in
favour of other group members
Individualistic life ? Sociality ? Eusociality
(superorganisms)
?
Joined parental care and defence
Cooperative breeding
Most bacteria and single cell eucaryotes
True multicellular organisms (Metazoa, Fungi,
Plantae
?
?
Colonies
Most primitive animals and plants
Social spiders, isopods, many insects,many
fishes Higher birds and mammals
Isoptera (autapomorphy) Some Aphidae and
Thripidae At least 14 independent lineages of
Hymenoptera Eucalyptus ambrosia beetles
(Australoplatypus incompertus) Sponge shrimp
(Synalpheus regalis) Naked mole
rats(Heterocephalus glaber and Cryptomys
damarensis)
?
?
Often intensive common parental care, aunt
behaviour, playing groups, and group defence
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All termites (Isoptera). They have male and
female workers and different casts.
All ants (Hymenoptera). They have female workers
only and highly differentiated cast systems.
Some eusocial Apidae and Vespidae (Hymenoptera).
They have female workers only.
Some bumble bees and other Apidae species may be
either solitary or eusocial depending on
environmental conditions.
Two species of mole rats have non-reproducing
workers and a queen. Colonies have up to 300
members.
Some Aphidae and Thripidae (Homoptera) have
sterile soldiers. Sometimes rudimentary parental
care.
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What favours Hymenoptera to become eusocial?
Hymenoptera are haplo-diploid organisms Fertilized
eggs become females Unfertilized eggs become
males
The haplo-diploid system
Queen King Daughter Son Brother 0.5 0.5 0.75 0.25
0.25 0 1.0 1.0 0 0.5 1.0 0 0.5 0.5 0.25
Daughter King Queen
Queen A,B
King C
The diploid-diploid system
Queen King Daughter Son Brother 0.5 0.5 0.5 0.
5 0.5 0 1.0 0.5 0.5 0.5 1.0 0 0.5 0.5 0.5
Son A
Daughter A,C
Daughter King Queen
Son B
Daughter B,C
Queen - daughter
Queen - sister
Hamiltons rule of inclusive fitness
Given that costs and benefits of reproducing are
similar it pays for a hymenopteran female more to
invest in her sisters than in her own brood.
This explains why eusocial Hymenoptera all have
sterile female workers and never sterile males.
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For instance a hymenopteran female helps her
sister at the cost of no reproduction. At
equlilibrum the number of surviving offspring
should be 2. Hence C 2
The sister raises one additional offspring
Even for one additional offspring of the sister
it pays to resign of own offspring
But be careful Most of the haplo-diploid
Hymenoptera are solitary. The theory requires
that queens a priori invest more in daughters
than in sons. Interestingly, many Hymenoptera
are able to decide whether to lay male or female
eggs. They are able to control sex
ratios Termites are diplo-diploid
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Eusociality and monogamy
Phylogenetic analysis shows that all ancestral
eusocial hymenopteran species were
monogame. Polygamy has derived after the
transition to eusociality. Polygamy never occurs
in species with totipotent workers.
From Hughes et al. 2008
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Todays reading
The game theory site http//www.holycross.edu/dep
artments/biology/kprestwi/behavior/ESS/ESS_index_f
rmset.html Selfish gene theory
http//en.wikipedia.org/wiki/Gene-centered_view_of
_evolution The evolution of eusociality
http//www.thornelab.umd.edu/Termite_PDFS/Evolutio
nEusocialityTermites.pdf Biology and sexual
orientation http//en.wikipedia.org/wiki/Biology_
and_sexual_orientation Biased sex ratios in man
http//huli.group.shef.ac.uk/lummaaproceedins1998.
pdfand http//www.jstor.org/cgi-bin/jstor/printpa
ge/00664162/di975349/97p0109i/0.pdf?backcontextpa
gedowhatAcrobatconfigjstoruserID9e4b1f37_at_umk
.pl/01cce4405a00501c7b1f10.pdfand
http//en.wikipedia.org/wiki/Gender_imbalance Figs
and fig wasps http//www.figweb.org/Interaction/
index.htm