A molecular phylogeny of the genus Echinococcus inferred from complete mitochondrial genomes

Abstract

Taxonomic revision by molecular phylogeny is needed to categorize members of the genus Echinococcus (Cestoda: Taeniidae). We have reconstructed the phylogenetic relationships of E. oligarthrus, E. vogeli, E. multilocularis, E. shiquicus, E. equinus, E. ortleppi, E. granulosus sensu stricto and 3 genotypes of E. granulosus sensu lato (G6, G7 and G8) from their complete mitochondrial genomes. Maximum likelihood and partitioned Bayesian analyses using concatenated data sets of nucleotide and amino acid sequences depicted phylogenetic trees with the same topology. The 3 E. granulosus genotypes corresponding to the camel, pig, and cervid strains were monophyletic, and their high level of genetic similarity supported taxonomic species unification of these genotypes into E. canadensis. Sister species relationships were confirmed between E. ortleppi and E. canadensis, and between E. multilocularis and E. shiquicus, regardless of the analytical approach employed. The basal positions of the phylogenetic tree were occupied by the neotropical endemic species, E. oligarthrus and E. vogeli, whose definitive hosts are derived from carnivores that immigrated from North America after the formation of the Panamanian land bridge. Host-parasite co-evolution comparisons suggest that the ancestral homeland of Echinococcus was North America or Asia, depending on whether the ancestral definitive hosts were canids or felids.