conflict and cooperation jacobus j. boomsma institute of biology university of copenhagen parasitism...
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CONFLICT AND COOPERATION
Jacobus J. Boomsma
Institute of Biology University of
Copenhagen
Parasitism versus Mutualism
Resource Allocation
Sex
Cooperation does not come easy
• Who gives alarm calls?• Can policing and punishment evolve?• Are policing and punishment necessary
for stable cooperation?• How important are kinship and
reciprocity?• How special are human societies?• Reciprocal exploitation and conflicts in
mutualisms
Evolution is essential for all biology
“Nothing in biology makes sense,
except in the light of evolution”
(Dobzhansky, 1973)
A Portrait Gallery of Evolutionary Biologists
1800 1850 1900 1950 2000
Malthus
Darwin
Wallace
Source of inspiration
A Portrait Gallery of Evolutionary Biologists
1800 1850 1900 1950 2000
Malthus
Darwin
Wallace
Mendel
Source of inspiration
A Portrait Gallery of Evolutionary Biologists
1800 1850 1900 1950 2000
Malthus
Darwin
Wallace
Mendel
Fisher
Haldane
Wright
Source of inspiration
A Portrait Gallery of Evolutionary Biologists
1800 1850 1900 1950 2000
Malthus
Darwin
Wallace
Mendel
Fisher
Haldane
Wright
Dobzhansky
Mayr
Source of inspiration
The roots of Behavioral Ecology: Tinbergen, Hamilton
and WilliamsTinbergen (1963)
Survival valueof behaviour
Hamilton (1964)
Evolutionaryroots of social behaviour
Williams (1966)
The first synthesis
Ecology is essential for understanding evolution
• “ Nothing in biology makes sense, except in the light of evolution ”
(Dobzhansky, 1973)
• “ Very little in evolution makes sense except in the light of ecology ”
(Townsend, Harper & Begon, 2000)
“Ecology provides the stageon which the “evolutionary play” is performed”
Darwinian Ecology
Evolutionary Ecology proper (animals, plants, micro-
organisms)
Behavioural Ecology (animals)
Sociobiology (social animals)
Darwinian Ecology
Natural selection and Sexual selection
Kin selection:The only realInnovation
after Darwin
e.g. Life Histories
Darwin’s Problem with Insect Societies
“ I……… will confine myself to one special difficulty, which at first appeared to me insuperable, and actually fatal to my whole theory. I allude to the neuters or sterile females in insect communities: for these neuters often differ widely in instinct and in
structure from both the males and the fertile females, and yet, from being sterile, they cannot propagate their kind.”
Darwin (1859) “The Origin of Species”
queen
workers
Hamilton’s Solution
Reproductive “altruism” evolves when:
br > c b = benefit (extra offspring of
relatives raised because of helping)
r = relatedness of donor to recipient
c = cost (own offspring not raised due to helping)
Parent-offspring conflict (Trivers 1974)
• Benefits gradually decrease per u.o.i.
• Costs stay constant or increase
• Parents weigh costs and benefits equally
• Offspring discount parental costs by their average relatedness to future sibs
Parent-offspring conflict (Trivers 1974)
• Young want more PI (y) than parents are selected to provide (p)
• y-p is even larger when current of future sibs have a different father (maximize B – C/4)
• Mother equally related to all offspring
• Offspring related to itself by r=1
Parent-offspring conflict theory
Dad 2
Dad 1
Mom
Parents Offspring
R.L. Trivers
Genetic relatedness
r = 0.25r = 0.5r = 1.0r = 0.5Parent-offspring conflict and sib-rivalry are relatedness-linked
Reciprocal altruism - The “ prisoner’s dilemma ”
1 2
Swap?
“Defection” is favoured. Mutual cooperation only pays in repeated exchanges.
1 2Defect Cooperate
1 2
1 2
1 2
1 2
Defe
ctC
oopera
te
“ Nature, red in tooth and claw ”
Tennyson (1850)
• Merciless• Exploitative• Fundamentally selfish
• Cooperation in nature needs to be explained by individual (gene) level selection and not by group selection
“Good for the species arguments”
Insect colonies as model systems
Simple ant colony in an acorn
Primitive waspcolony
2 cm 2 cm
From centimeters…...
Large insect colonies
Length: ~100 xArea: ~10 000 xMass: ~1 000 000 x
2 cm
2 m…. to meters
Advanced tropical ant colony
Previous slide
Large colonies are like societies
Tropical honey bee
Tropical waspTropical termite
Long-lived Elaborate nests
Simple and complex family structures
x
x
complexhalf-sib family
offspring
Parentsx
simplefull-sib family
daughter queenmates and takes over
x
x
Reproduction in haplodiploid social insects (ants, bees,
wasps)
Mother queen
father
Queen ovaries
workers
Not matedNo stored sperm
worker ovaries
worker sons
no Fertiliz ation
queen sons
noFertiliz ation
queen daughters
Fert ilization
Relatedness consequences of haplodiploidy
Mother queen
father
workers
queen sonqueen daughter
worker son
0.75
0.50 (own son)0.375 (other worker’s son)
0.25
0.500.25
0.50
0.500.25
0.00
Reproductive Conflict overSex ratio
and Male production
The conflict over Male Production
Mother queen
father
workers
queen sonqueen daughter
worker son
0.75
0.50 (own son)0.375 (other worker’s son)
0.25
0.500.25
0.50
0.500.25
0.00
When there are more half sisters thanfull sisters workers are selected to
remove each other’s eggs
Worker-Queen Conflict in Ants, Bees, Wasps
• Worker control over sex allocation is common
• Worker production of males is not
Who wins reproductive conflicts ?
In species with small colonies many try to reproduce but queens manipulate reproduction to their own advantage
Queens always win in Bumblebees
Who wins reproductive conflicts ?
In species with large colonies queens monopolize reproduction but workers raise sisters or brothers depending on their own best interests
Workers tend to win sex ratio conflicts in large ant societies
Nepotism is prevented by worker policing
• Queen eggs are marked with a queen pheromone
• Worker male eggslack this pheromone
• Worker eggs arerecognised by other workers and removed
• Worker policing is evolutionary stable in honey bees
Photos and data: Francis Ratnieks
Cooperation does not come easy
• Who gives alarm calls?• Can policing and punishment evolve?• Are policing and punishment necessary
for stable cooperation?• How important are kinship and
reciprocity?• How special are human societies?• Reciprocal exploitation and conflicts in
mutualisms
How special are Human Societies?
• We have culture !!!• But is culture really 100%
independent of genes?• How relevant is fitness in human
societies and can it be measured?• Do humans fit inclusive fitness
theory?• If so, what does this imply?• Cooperation does not come easy
Mutualistic Symbiosis and Co-evolution
mitochondria
gut bacteria
nitrogenbindingbacteria chloroplasts corals
mycorrhizae
lichens
termites and fungiants and fungi
Ectosymbionts of Insect Societies
The Conceptual Paradigm
“Many of the benefits sought by living things are disproportionally available to co-operating groups......
The problem is that while an individual can benefit from mutual co-operation, each one can also do even better by exploiting the co-operative efforts of others”.
R. Axelrod and W.D. Hamilton, The evolution of co-operation. Science 211: 1390-1396 (1981)
When and Why do Symbiotic Partners Cooperate?
• Exploitation and monopolization of novel resources
• Sufficient alignment of reproductive interests to stabilize interactions in spite of potential conflict
• ....... i.e., to allow Stable Bilateral Exploitation
Ant fungus-farming started simple
Mycocepurus nest
Dead Substrate:
Leaf debrisWood chipsInsect body partsInsect frass
The evolutionary history of fungus-growing ants
Leafcutters
Lower Attines
Higher Attines
Fungusrearing
SpecialClones
LeafcuttingHerbivory
Large Colonies
Ant Phylogeny:
Schultz & Meier (1995) and Schultz et al. unpublished
Mueller et al., 1998
Split into two genera, …… One of which became really
dominant, ……
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Biggggg..
An underground metropoliswhich may live for decades
A society with millions of workers, all daughters of the same long-lived queen
After Jonkman
And highly sophisticated
Atta
From Hölldobler and Wilson, 1990
castes
Acromyrmex
anal droplets gongylidia
The Leafcutter Ants
Fungus rearing Assembly Lines
• Evolution towards clonal fungi
• More genetic diversity of ants per nest via multiple queen mating
• Worker policing phenomena expected
Photo: Mark W. Moffett
Ongoing work Mischa Dijkstra
Villesen, Murakami, Schultz & Boomsma (2002)
Leafcutters
Lower Attines
Higher Attines
Leafcutter Ants Have Highly Harmonious Societies
Large Colonies, Worker Castes & Live Substrate associated with genetic diversity
Acromyrmex As Laboratory Model System
Three sympatric species inGamboa, Panama:A. octospinosusA. echinatiorA. insinuator (inquiline)
Division of labour
Ac. echinatior
0
0.1
0.2
0.3
0.4
0.5
0.6
0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
Head width (mm)
Pro
po
rtio
n o
f sa
mp
le
Internal
ForagersAcromyrmex echinatior
Data: Bill Hughes
Incompatibility Issues
Acromyrmex
0
1
2
3
0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0,45
Inco
mp
atib
ility
re
act
ion
Mean genetic distance
Inco
mpa
tibi
lity
Social parasites: Do not build nests, but simply move in
Acromyrmex echinatior host
Picture: Klaus LechnerParasites never carry Streptomyces
Parasite and host are sister species
The world’slargest and smallest ant
“Go to the ant, thou sluggard: consider her ways, and be
wise”Proverbs 6:6
The discussion program this afternoon
• A recapitulation of social insect conflicts • An experimental study of policing and
punishment in ants• Linking social evolution in insects and
vertebrates• How important is kinship in
vertebrates?
The conflict over Male Production
Mother queen
father
workers
queen sonqueen daughter
worker son
0.75
0.50 (own son)0.375 (other worker’s son)
0.25
0.500.25
0.50
0.500.25
0.00
Queen always values own son most (0.5)Worker always values own son most (0.5)
Workers prefer full sister sons (0.375) over queen sons (0.25)
Workers prefer queen sons (0.25) over half sister sons (0.125)
SPLIT SEX RATIO THEORYBoomsma & Grafen 1990, 1991
SINGLE MATINGHIGH RA
“SPECIALIZE IN FEMALES”
MULTIPLE MATINGLOW RA
“SPECIALIZE IN MALES”
rf = 0.75rm = 0.25
RA=3rf = 0.50rm = 0.25
RA=ca. 2
Formica truncorum Sex allocation
Queen singly mated Queen multiply mated
0
1
2
3
4
5
6
7
8
0 - 0.2 0.2 - 0.4 0.4 - 0.6 0.6 - 0.8 0.8 - 1.0
1989
Investment in females
Nu
mb
er
of
colo
nie
s