Evolutionary relationships in Trypanosoma cruzi: molecular phylogenetics supports the existence of a new major lineage of strains

For the purpose of investigating the evolutionary relationships among strai ns of the human parasite Trypanosoma cruzi, we have determined the nucleoti de sequence: in 16 T. cruzi stocks, of a DNA fragment having approximately 1030 nucleotides in length. Phylogenetic analyses show the presence of at l east three major groups of T, cruzi strains, a result that contradicts prev ious phylogenetic inferences based on polymorphism data. We also performed an analysis of the relative extent of nucleotide divergence among T. cruzi strains compared to the divergence between Leishmania species, using the ge ne encoding pteridine reductase. The results presented in this work show th at the divergence among the most distant T. cruzi strains is at least as hi gh as the divergence between two different species complexes of Leishmania, those containing L. major and L.. mexicana. (C) 2000 Published by Elsevier Science B.V. All rights reserved.