Transcript Formica truncorum

Conflict from
Cell to Colony
Tom Wenseleers
University of Leuven, Belgium
Ph.D. defence
May 22nd, 2001
Major transitions in evolution

Genes to Genomes

Prokaryotes to Eukaryotes

Unicellular to Multicellular Organisms

Organisms to Societies
Cooperation is
Key Feature in
Evolution of
Life on Earth
But potential for conflict

Cooperation seems obvious to
explain when viewed in terms of
species-level benefits

But erroneous logic: non-cooperative
’free-riders’ outcompete altruists

Conflicts may occur between organisms,
but also between cells or genes
(’intragenomic conflict’)
Potential for
Conflict in
Most Societies
Conflicts in insect societies
In what ratio should
males and females
Female
½ 3:1
¼Biased
Equal½
¾
Sex-Ratio be reared?
Sex-Ratio
F
M
Cytoplasmic sex-ratio distorters

Conflict also occurs at the
genomic level: maternally transmitted
genes favour more female biased sexratios than nuclear genes
(“intragenomic conflict”)

Cytoplasmic genes such as
mitochondria or some bacterial
symbionts may manipulate host to
produce female biased broods
(“cytoplasmic sex-ratio distorters”)
Wolbachia

Example of a maternally transmitted
symbiont

Alpha-proteobacterium

Occurs mainly in arthropods
(insects+Crustacea) + nematodes

Manipulates host reproduction to
favour own spread
Effects on host reproduction

Male Killing

Feminisation

Parthenogenesis Induction

Cytoplasmic Incompatibility
Female
Biased
Sex-Ratios
Cytoplasmic incompatibility
Inviable

Reduces fitness of
Uninfected Female x
Infected Male Crosses

Gives an advantage to infected
females

Sterility in diploids, but production
of males only in haplo-diploids
Normal
Offspring
Production
Phylogeny
Mitochondria
CMS
Caedibacter
MtK
Ehrlichieae
Rickettsia
MK
0.1
Wolbachia
Orientia
MK
Neorickettsia
Aims of my thesis

Part I : empirical
– Does Wolbachia occur in ant
societies?
– Alternative explanation for female
biased sex-ratios in this group?

Part II : theoretical
– What do animal and genomic
conflicts have in common?
– Can sociobiological theory be
applied to both?
Integrated approach
S e q u e n c e
o f
E v e n t s
Modelling
DNA Analysis
Experiments
Make predictions
Measure key
parameters
Formally test
hypotheses
Ideas
Molecular
Hypotheses
Experimental
Data
Data
Part I. Wolbachia - a cause
of intragenomic conflict
in ant colonies
Work plan

Does Wolbachia occur in ant societies
and if so in what frequency?

What effects does it have?
Three case studies :
–
–
–

Parthenogenetic species
Wood ant Formica truncorum
Leptothorax nylanderi
Host-parasite coevolution?
Methodology: PCR Assay

Polymerase Chain Reaction using
Specific Primers

Targets: ftsZ and wsp Wolbachia
genes

Positive, negative and nuclear DNA
(18S rDNA) controls

Negative samples retested twice
Sensitive
& Reliable
High Incidence Worldwide
3451 samples
Indonesia
Europe
A
# species=50
Chapter 1
Wenseleers et al. (1998)
Proceedings of the Royal Society of London
A+B
A
B
A+B
NI
NI
Chapter 6
# species=50
Florida
Panama
I
A
# species=7
Van Borm et al. (2001)
Journal of Evolutionary Biology
A+B
# species=10
Jeyaprakash & Hoy (2000)
Insect Molecular Biology
Morphological evidence

Present in trophocytes and
oocytes

Electron and light
microscopical (DAPI)
evidence
Work plan

Does Wolbachia occur in ant societies
and if so in what frequency?
YES, IN HIGH FREQUENCY

What effects does it have?
Three case studies :
– Parthenogenetic species
– Wood ant Formica truncorum
– Leptothorax nylanderi

Host-parasite coevolution?
Work plan

Does Wolbachia occur in ant societies
and if so in what frequency?
YES, IN HIGH FREQUENCY

What effects does it have?
Three case studies :
– Parthenogenetic species
– Wood ant Formica truncorum
– Leptothorax nylanderi

Host-parasite coevolution?
Parthenogenesis induction?
PCR Assay
6 Parthenogenetic Ants
and Cape Honey Bee
N=250
36 cols.
Grasso et al. (2000) Ethology, Ecology & Evolution 12:309-314
Wenseleers & Billen (2000) Journal of Evolutionary Biology 13:277-280
Were not infected.
Parthenogenesis
not induced by
Wolbachia.
Wolbachia in F. truncorum
With: Lotta Sundström
University of Helsinki
Formica truncorum

Extensive variation in sex-ratio produced
by different colonies

Linked to facultative sex-ratio biasing :
–
–

Workers kill brothers in colonies
headed by singly mated queen
But not in colonies with double mated
queen
Does Wolbachia affect the sex-ratio too?
Predictions
 Incompatibility
:
Effect on the sex-ratio
:
– Males and
queens
shouldless
be than
should
be infected
infected
queens equally
– Uninfected
colonies
should notwith
be
Sex-ratio should
be correlated
able
to survive
infection
rates
Formica truncorum

Males (96%) and queens (94%) infected
equally

All colonies infected (total # 33) despite
production of 6% uninfected queens by
each colony

Consistent with an incompatibility effect :
Uninfected queens do not survive past
the founding stage due to incompatible
matings
Wenseleers, Sundström & Billen (2002) Proceedings of the Royal Society of London series B, in press.
Investment in females
Infection and sex-ratio
1
0.75
r2 = 0.0097
0.5
0.25
0
0.00
0.20
0.40
0.60
0.80
1.00
Percent infected workers
GLM
Effects
F
p
No. of mates
Infection rate
Colony size
4.88
0.85
0.69
0.04
0.37
0.42
Wenseleers, Sundström & Billen (2002) Proceedings of the Royal Society of London series B, in press.
Infection and colony fitness
Sexual production
12
Per capita production
Per capita production
Worker production
2
r = 0.03
8
4
0
0.00
0.20
0.40
0.60
0.80
1.00
Proportion infected adult workers
12
r2 = 0.28
8
4
0
0.00
0.20
0.40
0.60
0.80
1.00
Proportion infected adult workers
GLM
Effects
F
p
F
p
No. of mates
2.11
0.16
2.5
0.13
Infection rate
2.89
0.11
10.2
0.005
Wenseleers, Sundström & Billen (2002) Proceedings of the Royal Society of London series B, in press.
Infection rates
Adaptive
clearance to
reduce colony
load?
p<0.015
p<0.0001
Percent infected
100
75
50
25
0
Sexuals
Worker
pupae
Adult
workers
N=296
N=158
N=387
Wenseleers, Sundström & Billen (2002) Proceedings of the Royal Society of London series B, in press.
Conclusions

No effects on the sex-ratio

Probably causes incompatible matings

Deleterious effects on colony function,
but partly mitigated by clearance of
infection in adult workers
Leptothorax nylanderi

Test experimentally whether Wolbachia causes incompatible matings

Setup: antibiotic treatment as an artificial means of creating the
uninfected queen x infected male crossing type

Prediction: male production (infertility) following antibiotic treatment
Antibiotics experiments
1
Primary sex-ratio
0.9
0.8
0.7
0.6
0.5
0.4
Untreated
Treated
4 colonies
N=70
7 colonies
N=152
2 = 10.51, p < 0.001
Work plan

Does Wolbachia occur in ant societies
and if so in what frequency?
YES, IN HIGH FREQUENCY

What effects does it have?
Three case studies :
– Parthenogenetic species
– Wood ant Formica truncorum
– Leptothorax nylanderi

Host-parasite coevolution?
Methodology: Sequencing
28 sequences
Aligned with previously sequenced relatives

Wolbachia surface protein wsp
was sequenced (approx. 550 bp)

Direct cycle sequencing when ants
were infected by single strain

Cloning and sequencing when ants
were infected by multiple strains
(TA-cloning kit, pUC57 vector)
Solenopsis invicta (imported)
High strain diversity
0.050
(25 MY)
A
B
Solenopsis invicta (imported)
No match with host phylogeny
Hosts diverged
35 MY ago, but
share a recently
evolved W. strain
(1.7 MY old)
0.050
(25 MY)
A
B
Solenopsis invicta (imported)
Multiple infections
0.050
(25 MY)
A
Multi infections
may drive speciation
events!
B
No match with host phylogeny
Formica hosts...
...and their symbionts
rufa
truncorum
polyctena
polyctena
pratensis
pratensis
truncorum
84
100
lemani
lemani
fusca
fusca
rufa
O
O
Gyllenstrand, unpublished
99
100
0.02
(10 MY)
Work plan

Does Wolbachia occur in ant societies and
if so in what frequency?
YES, IN HIGH FREQUENCY

What effects does it have?
Three case studies :
– Parthenogenetic species
– Wood ant Formica truncorum
– Leptothorax nylanderi

Host-parasite coevolution? NO, OCCASIONAL
HORIZONTAL TRANSMISSION
Part II. Theoretical aspects of
conflict and cooperation
With: Francis Ratnieks and Kevin
Foster
University of Sheffield
Animal vs. intragenomic conflict

What do animal and
intragenomic conflict have in
common?

Is there a “general theory of
conflict” that provides insight
into the evolution of conflict at
both levels?
Theories of conflict
Two Approaches in the
Study of Conflict
Game Theory
von Neumann &
Morgenstern
Kin Selection
Hamilton
Cost Depends
on Social Context
r.B > C
Single method
Generalised Hamilton’s rule
Consequence
Regression
of
of genotype
both cooperating
on joint behaviour
B.r - C +E j .βjg > 0
Hamilton’s rule Terms that
(costs & benefits take into
independent account social
of social context) context
Wenseleers & Ratnieks submitted
Animal vs. intragenomic conflict
HAWK
0
-B
DOVE
DOVE
B
-C
COOPERATE
GENOMIC CONFLICT
(MEIOTIC DRIVE)
ANIMAL CONFLICT
COOPERATE DRIVE
1/2
GDC.(1-k)
GDC.k
GDD/2
Animal vs. intragenomic conflict

Shows that game theoretic logic of conflict at
both levels is the same

But can genes also be related?

Yes, kinship measures genetic correlation and
for 2 genes at a locus this is the inbreeding
coefficient FIT

When genes are related they are selected to
be altruistic !

Application of generalised Hamilton’s rule
allows detailed analysis
Spite: Hamilton’s unproven theory

Medea killed her children to take
away the smile from her husband’s
face.

Example of a paradoxical behaviour
that harms another at no benefit to
self (“spite”)

We showed that some forms of
intragenomic conflict qualify as
spiteful behaviour
(Maternal effect lethals, queen killing
in the fire ant)
Foster, Ratnieks & Wenseleers (2000) Trends in Ecology & Evolution 15:469-470
Foster, Wenseleers & Ratnieks (2001) Annales Zoologici Fennici, in press
Why become a worker?

Why do social insect females work for
the benefit of others?

Usual explanation: indirect genetic
benefit when altruism is directed towards
relatives (’kin selection’)

But is relatedness in insect societies high
enough?

E.g. honey bee: queen mates with
several males so that workers mostly
rear half-sisters (r=0.3)
New calculations

Female should become a queen with a
probability of (1-Rf)/(1+Rm) (self determination)
– = 20% for stingless bees (singly mated)
– = 56% for honey bees (polyandrous)

Too high for the colony as a whole, since
queens are only needed for swarming
(“tragedy of the commons”)

Adult workers and mother queen selected to
prevent production of excess queens (“policing”)
Comparative
predictions
THE SAME TENSION
OCCURShold
IN HUMAN SOCIETY !
stingless bees
honey bees
Individual
Freedom
Causes a
Cost to
Society
Efficient
But
females
Society
but
prefer
to become
with
Noqueen
Individual
probability
Freedom
of 56% !
Self determination
20% queen production
Policing of caste fate
0.02% queen production
General conclusions

Part I : empirical
– Does Wolbachia occur in ant societies?
YES, IN HIGH FREQUENCY
– Alternative explanation for female biased sex-ratios
in this group? PROBABLY NOT
– Other effects? INCOMPATIBILITY (SPECIATION?)

Part II : theoretical
– What do animal and genomic conflicts have in
common? SAME LOGIC
– Can sociobiological theory be applied to both?
YES (GENERALISED HAMILTOM’S RULE)
– What do we learn from this more generally?
DEEPER INSIGHT INTO THE FUNCTIONING OF
HUMAN SOCIETIES (TOC)
The End
Acknowledgements
Prof. Dr. J. Billen
Prof. Dr. R. Huybrechts
Prof. Dr. J.J. Boomsma
Dr. F. Ito
Dr. K.R. Foster
Dr. F.L.W. Ratnieks
Prof. S.A. Frank
Dr. L. Sundström
Dr. D.A. Grasso
Drs. S. Van Borm
Prof. Dr. F. Volckaert
Academy of Finland,
British Council,
FWO-Vlaanderen,
Vlaamse Leergangen,
EU Network “Social Evolution”