EVOLUTION AND PHYLOGENY OF WOLBACHIA - REPRODUCTIVE PARASITES OF ARTHROPODS

Wolbachia are cytoplasmically inherited bacteria found in reproductive tissues of many arthropod species. These bacteria are associated with reproductive alterations in their hosts, including parthenogenesis, r eproductive incompatibility and feminization. A fine-scale phylogeneti c analysis was done using DNA sequences from ftsZ, a rapidly evolving bacterial cell-cycle gene. ftsZ sequences were determined for 38 diffe rent Wolbachia strains from 31 different species of insects and one is opod. The following results were found: (i) there are two major divisi on of Wolbachia (A and B) which diverged 58-67 millions years before p resent based upon synonymous substitution rates; (ii) a general concor dance is found between the ftsZ and 16S rDNA phylogenies, indicating t hat these represent bacterial strain (rather than simply gene) phyloge nies; however, a possible example of recombination between A and B div ision bacteria may have occurred in the feminizing- Wolbachia present in an isopod; (iii) extensive horizontal transmission of Wolbachia has occurred between insect taxa, including different insect orders; one strain in particular (designated Adm) shows extensive recent horizonta l transmission; (iv) there is an association between the Wolbachia fou nd in a parasitic wasp (Nasonia) and its fly host (Protocalliphora), s uggesting exchange of bacteria between these species; (v) parthenogene sis induction has evolved several times among the Wolbachia; and (vi) some insects harbour infections with more than one Wolbachia strain, e ven within individual insects.