PHYLOGENY AND EVOLUTION OF THE PIROPLASMS

Small subunit ribosomal RNA (srRNA) genes of three Theileria species, one Cytauxzoon and four Babesia species were amplified using the polym erase chain reaction (PCR), cloned and sequenced. Our sequences were a ligned with srRNA sequences previously published for eight species of Apicomplexa, one ciliate and one dinoflagellate, the last two being in cluded as free-living outgroup species. Phylogenetic relationships bet ween the organisms were inferred by four independent methods of phylog enetic tree construction using the ciliate Oxytricha nova to root the trees. Our trees fail to show a consensus branching order. They do, ho wever, clearly indicate that the theilerias form a monophyletic taxon derived from a paraphyletic group which includes the species B. equi, C. felis and B. rodhaini. The distance trees indicate that the babesia s sensu stricto (B. canis, B. caballi, B. bigemina and B. bovis) form another monophyletic taxon which diverged before the theilerias separa ted from the above-mentioned paraphyletic group. The parsimony and max imum likelihood trees suggest that the babesias and theilerias are sis ter taxa, both of which were derived from the paraphyletic group.