Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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”