or why consent to social oppression
T. Wenseleers,
University of Sheffield

 conflicts occur in most societies
 how are conflicts resolved?
 Kin selection
 Recriprocity (tit-for-tat)
 Reputation (humans)
 Policing
 Punishment
NON-COERCIVE
COERCIVE

 occurs in three contexts :
 conflict over male parentage
(eating of worker laid eggs by queen or workers)
 conflict over caste fate in societies with morph. castes
(caste fate policing by food control)
 conflict over queen replacement
(prevention of queen overthrow)

 policing reduces benefit of attempted selfishness
 could this favour individuals not even to attempt to behave selfishly ?
 idea of “self policing” or “acquiescence” = to agree without protest to a system of policing

 formally investigate the likelihood for the evolution of acquiescence
 models specific for social insects, where several types of policing occur

 occurs in three contexts :
 conflict over male parentage
(eating of worker laid eggs by queen or workers)
 conflict over caste fate in societies with morph. castes
(caste fate policing by food control)
 conflict over queen replacement
(prevention of queen overthrow)

Workers lay male eggs… r own sons
> r queen’s sons
…but these are eaten by other workers r other workers’ sons
< r queen’s sons
“worker policing”

Females would generally benefit from becoming a queen rather than a worker
“caste fate conflict”
But workers only provision a few
“royal cells” with sufficient food to allow queen development
Females in other cells are forced to develop as workers
Bourke & Ratnieks BES 1999, Wenseleers, Ratnieks & Billen J. Evol. Biol. in press

Policed by fellow workers
“pretender punishment”
Selfish ant attempts to overthrow current breeder
Monnin & Ratnieks BES 2001, Monnin et al. Nature 2002

Normal queen lifespan (100%)
Nonproductive
‘Lag period’ length L
Early queen replacement
 Benefit of early replacement: no risk of queen being replaced by sister at later time
 Cost of early replacement: drop in average colony productivity, since it takes time for new queen to reestablish

Selects for workers to police ‘early replacers’

100%
COLLECTIVE OPTIMUM

PREVENT EARLY OVERTHROW
Single mating
Double mating
80%
60%
50%
40%
INDIVIDUAL
OPTIMUM = L(1+R m
)/(1-R f
) = 0.1x1.25/0.25
20%
All males queen’s sons
All males workers’ sons
0% 10% 20% 30% 40%
Productivity cost of early replacement L
50%

In Trigonini stingless bees, e.g. Plebeia remota prevents virgin queens from selfishly overthrowing mother queen “preemptive policing”
Workers force virgin queens to build their own prison and queens that escape from their prison are executed

?
Conflict over It is selfish Policing via Acquiescence
Male parentage For a worker to lay eggs
Caste fate To become a queen
Queen replacement
To replace current queen
Cannibalization of w/laid eggs
Food control
Aggression or imprisonment
Worker sterility
Accept worker caste fate
Not attempt to replace queen

 If workers reproduce, but their eggs are policed, could it favour workers not to lay eggs in the first place
 i.e. could policing secondarily select for worker sterility?
NEW THEORY: YES

 single worker selected to lay when
1
 q
P
.( R son

R brother
)

1 n
.
R brother

1 n
.
R sister

0
 shows that benefit of worker laying reduces as the efficiency of policing P goes up
 policing can potentially make it unprofitable for any worker to lay

 ESS fraction of laying workers z *

 
B
2 
4 AC
2 A with A
 
2 n
2
(1

P
2
) (1

R f
)
B
 n

P n

P )(1

R f
)
 q

R f
))
C

( (1

P )
 q (1 4 R f
))
 Function of colony size ( n ), relative queen fecundity
( q ), sister-sister relatedness ( R f
) and probability that worker-laid eggs are policed ( P )

 when there is no policing ( P =0) and for large n ,
ESS is for colony to have ratio of
R son
R nephew to R nephew
+ R sister laying workers sterile workers i.e. z* =(1R sister
)/(1+ R sister
)
=14% under single mating
 but fewer workers selected to lay when there is a high chance that their eggs are policed

honey bee, polyandrous queen
0.5
0.4
0.3
0.2
0.1
single monandrous queen
0.2
0.4
0.6
Efficiency of policing (P)
0.8
1

Empirical data : honey bees and vespine wasps
Dolichovespula saxonica
Dolichovespula sylvestris
5.00
Dolichovespula media
0.50
Apis cerana
Vespa crabro
Vespula vulgaris
0.05
84

= -0.8, p < 0.01
86
Apis mellifera
88 90 92 94 96 efficiency of policing
(% of worker eggs eaten)
98 100


Only 1 in 10,000 workers lay eggs

Model’s predictions





 n = 35,000 workers q = 25 (counting only queen’s male eggs)
R f
= 0.3 (multiple mating)
If policing were absent : 54% of all workers should lay
But as a result of highly effective policing there is less to gain from laying e.g. with P = 0.99 only 1 in 10,000 laying workers predicted
Fits observed data very well

Theoretically predicted values
14

= 0.8, p < 0.01
12
Dolichovespula saxonica
10
8
Dolichovespula sylvestris
6
Dolichovespula media
4
Apis cerana
2
Vespa crabro
Vespula vulgaris
0
Apis mellifera
1
Using best-fit colony-level cost function y = (1-x) k
0.5
vespine wasps k = 1.5
0
0 honey bees k = 5.7
0.5
% of laying workers
0 2 4 6 8 10 12 14 theoretically predicted % of laying workers
1
16

 Given that there are individuals benefits of developing as as queen, why do females accept their worker caste fate?
 Even when females are only given little food they could potentially evade their caste fate by becoming a dwarf queen
 Occurs in stingless bees and some ants

2 mm
Stingless bee
Plebeia remota dwarf queen normal queen

 dwarf queens may have lower fecundity than normal queens
 producing 100% of sister’s offspring
(r = 0.375) is as good as producing 75% own offspring (r = 0.5) !
 favours acquiescence

Schwarziana quadripunctata
 89% of all queens produced are dwarf queens
 Yet only 31% of all colonies are headed by dwarf queens
 Seems to be the result of favouritism: workers selectively kill dwarf queens and prefer to swarm with normal queens
 This also reduces the benefit of becoming a dwarf queen

single mating, all males queen’s sons
0.2
0.15
0.1
0.05
single mating, all males workers’ sons
Schwarziana quadripunctata
0.2
0.4
0.6
0.8
Worker preference for normal queens (P)
Parameters: 1 in a 100 cells are normal sized queen cells
1

 Dinoponera ants: workers are selected to overthrow mother at
50% her normal lifespan, but attempted overthrow is punished

Does punishment of “pretenders” reduce the conflict?
 YES, it reduces the benefit of becoming a dominant “resisting” worker

0.2
0.15
0.1
0.05
All males gamergate’s sons
All males workers’ sons
0.2
0.4
0.6
0.8
Effectiveness of pretender punishment (P)
1


Varied mechanisms of policing in social insects - aggression, imprisonment, punishment, etc…

Policing does not just repress individual selfishness, it also makes it unprofitable for individuals to act selfishly in the first place

Can explain why
 workers in many species are sterile
 females usually accept worker caste fate
 breeder isn’t always challenged in totipotent societies

 Collaborators
 Steve Frank, Adam Hart, Heikki Helanter ä,
Thibaud Monnin, Francis Ratnieks
 Funding
 INSECTS network
 EC Marie Curie Fellowship