PHYLOGENETIC-RELATIONSHIPS AMONG 8 EIMERIA SPECIES INFECTING DOMESTIC-FOWL INFERRED USING COMPLETE SMALL-SUBUNIT RIBOSOMAL DNA-SEQUENCES

Complete 188 ribosomal RNA gene sequences were determined for 8 Eimeri a species of chickens and for Eimeria bovis of cattle. Sequences were aligned with each other and with sequences from 2 Sarcocystis spp., To xoplasma gondii, Neospora caninum, and 4 Cryptosporidium spp. Aligned sequences were analyzed by maximum parsimony to infer evolutionary rel ationships among the avian Eimeria species. Eimeria bovis was found to be the sister taxon to the 8 Eimeria species infecting chickens. With in the avian Eimeria species, E. necatrix and E. tenella were sister t axa; this clade attached basally to the other chicken coccidia. The re maining Eimeria spp. formed 3 clades that correlated with similarities based on oocyst size and shape. Eimeria mitis and Eimeria mivati (sma ll, near spherical oocysts) formed the next most basal clade followed by a clade comprising Eimeria praecox, Eimeria maxima, and Eimeria bru netti (large, oval oocysts), which was the sister group to Eimeria ace rvulina (small, oval oocysts). The 4 clades of avian Eimeria species w ere strongly supported in a bootstrap analysis. Basal rooting of E. ne catrix and E. tenella between E. bovis and the remaining Eimeria speci es and the apparent absence of coccidia that infect the ceca of est th at E. necatrix and E. tenella may have arisen from a host switch, perh aps from the North American turkey, Meleagris gallopavo.