Evolution of the genus Leishmania revealed by comparison of DNA and RNA polymerase gene sequences.

Previous hypotheses of Leishmania evolution are undermined by limitations in the phylogenetic reconstruction method employed or due to the omission of key parasites. In this experiment, sequences of the gene encoding the DNA polymerase alpha catalytic polypeptide (POLA) were analysed phylogenetically in combination with those encoding the RNA polymerase II largest subunit gene (RPOIILS) to infer a comprehensive phylogeny of Leishmania. Nineteen species of parasites were studied, comprising representatives of each Leishmania species-complex (Leishmania Leishmania tropica, Leishmania Leishmania donovani, Leishmania Leishmania mexicana, Leishmania Leishmania hertigi and Leishmania Viannia braziliensis), as well as parasites of questionable taxonomy (Leishmania herreri, Sauroleishmania adleri, Sauroleishmania deanei, Sauroleishmania gymnodactyli and Sauroleishmania tarentolae). The analyses presented here provide strong support for the hypothesis that the Leishmania that infect reptiles (also known as Sauroleishmania) evolved from mammalian Leishmania. One implication of this finding is that the taxonomic definition of Leishmania should be broadened to encompass characteristics of the reptilian parasites. However, this taxonomic revision is complicated in that Leishmania (L.) hertigi, Leishmania (L.) deanei and Leishmania herreri, which exhibit some biological properties of Leishmania, are more closely related to Endotrypanum on the basis of these sequence comparisons. Consequently, the taxonomic discrimination between Leishmania that infect mammals, Leishmania that infect reptiles and Endotrypanum may be more problematic than has been previously thought. Since our resulting phylogenetic hypothesis is supported by the analyses of two different genes, we speculate on the origin and evolutionary expansion of this lineage of kinetoplastid protozoa.