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.

Phylogenetic Pattern, Evolutionary Processes and Species Delimitation in the Genus Echinococcus

“…shiquicus, the nuclear DNA phylogenies of Knapp et al (2011) are in agreement with the mtDNA phylogenies of Nakao et al (2007Nakao et al ( , 2013b and Hüttner et al (2008), while the phylogeny of Saarma et al (2009) suggests a different topology. With respect to E. canadensis, all phylogenies indicate a monophyletic origin, except for that based on exon sequences of nuclear DNA genes by Knapp et al (2011), which suggests that the G6 genotype is more closely related to E. ortleppi than to the other genotypes of E. canadensis.…”

“…Le et al, 2002;McManus et al, 2002;Obwaller et al, 2004;Lavikainen et al, 2003Lavikainen et al, , 2006Thompson et al, 2006;Nakao et al, 2007Nakao et al, , 2013bHüttner et al, 2008;Moks et al, 2008) and nuclear DNA sequences (e.g. Lavikainen et al, 2003;Bart et al, 2006;Saarma et al, 2009;Knapp et al, 2011).…”

“…Initial taxonomic revisions split E. granulosus (sensu lato) into three species; E. equinus for G4, E. ortleppi for G5 and E. granulosus sensu stricto for G1, G2 and G3 Thompson and McManus, 2002). Nakao et al (2007) subsequently proposed that the remaining strains (G6, G7, G8 and G10) be afforded species status as E. canadensis. In addition to these taxonomic changes, Xiao et al (2005) described a new species (E. shiquicus), closely related to E. multilocularis, from Tibet, and Hüttner et al (2008) resurrected the species E. felidis, originally described by Ortlepp (1934Ortlepp ( , 1937) from South Africa.…”

“…In many cases, where there have been no obvious differences in morphology between putative species, a genetic yardstick has been used; species status has been recommended if taxa are as genetically different from each other as the difference between well-established species in the same or related genera (e.g. Thompson and McManus, 2002;Nakao et al, 2007;Hüttner et al, 2008). While a genetic yardstick approach may sometimes provide a useful guide to species status, it is essentially an appeal to authority, or at least to past practice.…”

The molecular epidemiology of parasite infections: Tools and applications

“…Organisms following the same evolutionary trajectory should be monophyletic (derived from the same ancestral taxon) and exclusive (more closely related to each other than they are to any individuals outside the group) [94]. The morphologically defined species Echinococcus granulosus, for example, has now been split into a number of different species, because phylogenies based on mtDNA sequence data indicate that strains of E. granulosus are not monophyletic [95,96].…”