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



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tarix20.12.2017
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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 :

  • 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





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