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 ½ ½ be reared?

Sex-Ratio

F M

Cytoplasmic sex-ratio distorters

 Conflict also occurs at the genomic level: maternally transmitted genes favour more female biased sex ratios 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

Mitochondria CMS

Phylogeny

Caedibacter MtK

Ehrlichieae 0.1

Rickettsia MK Orientia MK Wolbachia

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

Make predictions

DNA Analysis

Measure key parameters

Experiments

Formally test hypotheses

Ideas Hypotheses Molecular Data Experimental 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 # species=50

Chapter 1 Wenseleers

et al.

(1998)

Proceedings of the Royal Society of London

A A+B NI Europe A B A+B NI

Chapter 6

# species=50 Florida Panama # species=7

Van Borm

et al.

(2001)

Journal of Evolutionary Biology

A A+B I # 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

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.

Infection and sex-ratio

1 0.75

0.5

0.25

0 0.00

r 2 = 0.0097

0.20

0.40

0.60

Percent infected workers 0.80

1.00

GLM Effects No. of mates Infection rate Colony size F 4.88

0.85

0.69

p 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

12 8 4 Worker production r 2 = 0.03

12 8 4 Sexual production r 2 = 0.28

0 0.00

0.20

0.40

0.60

0.80

Proportion infected adult workers 1.00

GLM Effects No. of mates Infection rate F 2.11

2.89

p 0.16

0.11

0 0.00

0.20

0.40

0.60

0.80

Proportion infected adult workers 1.00

F 2.5 10.2 p 0.13

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

100 75 50 25 0 Sexuals N=296 Worker pupae N=158 Adult workers 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 0.9

0.8

0.7

0.6

0.5

0.4

Untreated 4 colonies N=70 Treated 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 s

urface 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)

A High strain diversity 0.050

(25 MY) B

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

A Multiple infections 0.050

(25 MY) Multi infections may drive speciation events!

B

No match with host phylogeny

Formica hosts...

rufa polyctena pratensis truncorum lemani fusca O Gyllenstrand, unpublished ...and their symbionts truncorum polyctena 84 100 pratensis lemani fusca rufa 100 O 99 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 Cost Depends on Social Context Game Theory

von Neumann & Morgenstern

Kin Selection

Hamilton

Single method r.B > C

Generalised Hamilton’s rule

B.r - C +E .

j

β

jg

> 0

Hamilton’s rule Terms that (costs & benefits of social context) take into independent account social context Wenseleers & Ratnieks submitted

Animal vs. intragenomic conflict

ANIMAL CONFLICT GENOMIC CONFLICT (MEIOTIC DRIVE) DOVE HAWK 0 -B B -C COOPERATE DRIVE 1/2 G DC .(1-k) G DC .k

G DD /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

F IT

 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-R f )/(1+R m ) (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

”)

IN HUMAN SOCIETY !

stingless bees honey bees Individual Freedom Causes a Cost to Society 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. J.J. Boomsma Dr. K.R. Foster Prof. S.A. Frank Dr. D.A. Grasso Prof. Dr. R. Huybrechts Dr. F. Ito Dr. F.L.W. Ratnieks Dr. L. Sundström Drs. S. Van Borm Prof. Dr. F. Volckaert Academy of Finland, British Council, FWO-Vlaanderen, Vlaamse Leergangen, EU Network “Social Evolution”