Conflict and cooperation in animal societies
the role of internal state
Zoltán Barta
[email protected]
16th Annual European Meeting of PhD Students in Evolutionary Biology
23th -28th May 2010, Wierzba, Poland
Conflicts
Cooperation
Conflict and cooperation
social dilemma
gain depends on collective investment
investment is costly
☞ conflict of interest
everybody likes the others to invest more in public goods
two solutions of social dilemma:
conflict
exploitation
exploited loose a lot, exploiter gain a lot
☞
cooperation
everybody invests, everybody enjoys the benefits
everybody gain some
☞
conflict and cooperation are the two sides of the same coin
What’s this talk about?
Internal state is important.
hungry – well-fed
lean – fat
low – high level of
testosterone
⇔
Internal state is often
neglected.
How does the internal state influence the outcome of social
dilemma?
Three case studies:
parental care vs. reserves
social foraging vs. reserves
cooperation vs. helpfulness
Defence against exploitation:
parental care vs. energetic reserves
The distribution of care patterns – a few example
Species
Birds
Little Egret
Snail Kite
Kentish Plover
Penduline Tit
Amphibians
E. johnstonei
Fish
St Peter’s fish
I. nebulosus
bipar.
carea
male
only
carea
female
only
carea
40.0
22.2
9.1
0.0
44.0
50.0
81.8
17.9
4.0
27.8
9.1
47.8
12.0
0.0
0.0
34.3
Fujioka 1989
0.0
64.3
35.7
0.0
Bourne 1998
74.7
56.2
8.1
39.3
17.2
4.5
0.0
0.0
Balshine-Earn 1995
a: percentage of broods
bipar.
Reference
desertiona
Beissinger & Snyder 1987
Székely & Lessels 1993
Persson & Ohrström 1989
Blumer 1986
The parental conflict about care
parental care improves offspring’s survival
care is costly
reduced future survival
reduced chance of remating
cost of care can be avoided by deserting the brood if
one parent can raise the brood
partner will continue to care
conflict of interest: which of the parents should care?
the sex deciding first can force the other sex to care by deserting
Simultaneous vs. sequential decisions
members of the pair decide independently of each other
male:
female:
female
care
desert
female
care
desert
care
5
3
care
5
6
desert
3
2
male
male
desert
4
2
male decides first, female then decides on the basis of the male’s
decision
male:
female:
female
care
desert
female
care
desert
care
5
3
care
5
6
desert
3
2
male
male
desert
4
2
Why do we need a dynamic modell of parental care?
previously: arbitrary pay-offs
in reality the pay-offs depend on
behaviour of current mate
own future behaviour
past and future behaviour of others in the population
need to model the past and future of the population to get the
pay-offs
Solution
state-dependent dynamic game model of parental care
The outline of the model
time scale: one breeding season of T = 100 days.
state variables: marital status, own and mate’s energy reserves.
behavioural actions:
unmated individuals : rest, forage or search for a mate,
mated individuals : after producing a batch of offspring the parents
either cares or deserts.
decision about care: sequential, the male decides first
cost of care: energy and time
uni- and biparental care similarly efficient
strong conflict of interest about who should care
☞
0.00 0.01 0.02 0.03 0.04 0.05 0.06
Frequency of care
Results: no effects of reserves
biparental
female only
0
20
40
60
80
Time, t
The male forces the female to care by deserting her.
25
20
15
female
10
biparental
male
5
Mean reserves
0.020
0.010
male
only
female only
0
0.000
Frequency of care
Results: reserves are important
0
20
40
Time, t
60
80
0
20
40
60
80
Time, t
The female circumvent the male’s behaviour by keeping her reserves
below the cost of care.
Parental care game: conclusions
The sequence is important!
Only credible threat works.
low energy reserves guarantees credibility
Strategic regulation of body mass can be important in parental
conflict about care.
Social foraging:
from exploitation to insurance
Social foraging: foraging in groups
group mates
☞ chance to exploit others
common in ground-feeding passerines
two food finding behaviour in the group:
producing
scrounging
The basic model
strong negative frequency dependence of scroungers’ payoff
Pay-off
evolutionarily stable strategy (ESS)
scroungers
producers
ESS
0.0
0.2
0.4
0.6
0.8
Proportion of scroungers
1.0
Basic model: exploitation
0.6
0.4
0.2
0.0
ESS pay-off
0.8
1.0
without scroungers
0.0
0.2
0.4
0.6
0.8
ESS proportion of scroungers
1.0
Problems with the basic model
Assumptions
simplistic environment
Consequences
☞
predation?
stochasticity in food?
everybody is the same
☞
dominance?
spatial position?
reserves?
Solution
state-dependent stochastic dynamic game model of
producing-scrounging
The model
social foraging over a couple of winter days
maximising daily survival
behaviour
daytime: rest, forage (produce, scrounge)
night: rest
state variable: energy reserves
80
Results: optimal strategy
40
20
0
Reserves
60
rest
produce
scrounge
0
5
10
15
Time of day
20
25
30
0.2
0.3
0.4
0.5
producer only
producer-scrounger
0.0
0.1
Overwinter survival
0.6
0.7
Results: overwinter survival
10
20
50
Amount of food
Use of scrounging improves winter survival.
100
Producing - scrounging: conclusions
use of scrounging depends on internal state
scrounging as explorative strategy?
yes: its use decreases others’ gain
BUT: the possibility of scrounging increases everybodies’ survival
The rise of cooperation:
state-dependent generalised reciprocity
Cooperation
benefitial, but risky
big temptation to cheat
Cooperation
cooperators are more successful than
non-cooperators
BUT
among cooperators cheating is the
best
How can cooperation evolve?
Cooperation among non-kins needs some
“helping” mechanism.
Reciprocity
Direct reciprocity
Indirect reciprocity
I scratch your head
and you’ll scratch
mine . . .
It has never bitten
a client. . .
based on reputation
➽
back and forth helping between
non-kins
It has never eaten
a cleaner. . .
advanced cognitive capabilities
☞
minor importance in animals
New kid on the block
Generalised reciprocity
I help you because
someone else has
helped me . . .
among anonymous partners
simple mechanism
☞
the role of internal state???
A neglected constraint: internal state
Internal state can influence social behaviour.
mental mood: gratitude, hate, anger. . .
neurotransmitters/hormones
oxitocin
serotonin
Models of cooperation usually neglect these.
Simple model of generalised resiprocity
recipient
actor
helps
I) Kact ≥ 0.5
not helps
II) Kact < 0.5
no cooperation
Actual helpfulness, Kact
State-dependent model of generalised reciprocity
helps
not helps
Interactions
Traits:
Kini : initial helpfulness;
Kdec : decrement of helpfulness (it has not been helped);
Kinc : increment of helpfulness (it has been helped)
The rise of cooperation
0.4
0.8
K i ni
K d ec
K i nc
0.0
Trait values
(a)
0
50000
100000
150000
200000
150000
200000
Generations
(b)
0.4
0.0
Probability
0.8
prob. of helping after defection
prob. of helping after cooperation
prop. of helping
0
50000
100000
Generations
0.8
0.6
0.4
0.2
b; n M
3; 40
3; 80
5; 40
3; 40*
0.0
Proportion of cooperative populations
1.0
Effect of group size
0
10
20
30
Group size, M
40
50
1.0
0.8
0.6
0.4
0.2
b; M
3; 10
3; 20
5; 10
0.0
Proportion of cooperative populations
Effect of number of interactions
2
5
10
20
50
Expected number of rounds, n M
100
Generalised reciprocity: conclusions
cooperation under a wide range of conditions
anonymous players
large groups
moderate number of interactions
very simple framework
one internal state variable
update rules through gradual evolutionary steps
no advanced cognitive abilities
➽
state-dependent generalised reciprocity:
a basis for the evolution of complex social behaviour???
General conclusions
Internal state may have an important role in determining the outcome
of social dilemma.
avoiding force, credible threat
insurrance instead of exploitation
cooperation through simple, gradual evolutionary steps
Acknowledgements
Co-authors: Luc-Alain Giraldeau, Alasdair I. Houston, Dóra B.
Huszár, John M. McNamara, Tamás Székely, Michael Taborsky.
Finance: Leverhulme Trust Linked Fellowship, NATO Science
Fellowship, INCORE, Hungarian Scientific Research Fund.
LATEX