Sex allocation Wolbachia Maternally transmitted symbiont that manipulates host to produce female biased broods

My research

Sex allocation

Wolbachia

• Maternally transmitted symbiont that manipulates host to produce female biased broods

• “Cytoplasmic sex ratio distorter”

• Alpha-proteobacterium

• Occurs mainly in arthropods (insects+Crustacea) + nematodes

Effects on host reproduction

• Male Killing

• Feminisation

• Parthenogenesis Induction

Cytoplasmic incompatibility

• 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

Aims

• 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

Methodology: PCR Assay

Aims

• 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?

Aims

• 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?

Wolbachia in F. truncorum

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

Infection rates

Clearance in lab experiments

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

Aims

• 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

• 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)

Wolbachia in Leafcutter Ants

Wolbachia in Leafcutter Ants

No match with host phylogeny

Sequencing conclusions

• No host-parasite coevolution

• But distinct ant Wolbachia clades – implies degree of host specialisation

• Frequent horizontal transmission

• Single ants may be infected with up to 6 different strains

• Different populations usually, but not always, infected by same strains

Conclusions

• Does Wolbachia occur in ant societies? YES, IN HIGH FREQUENCY

• Alternative explanation for female biased sex-ratios? NO STRONG EVIDENCE Other effects? INCOMPATIBILITY (SPECIATION?)

• Host-parasite coevolution? NO, OCCASIONAL HORIZONTAL TRANSMISSION

References