Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 15, 1999
Publication Date: N/A
Interpretive Summary: Tapeworms of the genus Taenia are of considerable medical and veterinary significance, and include 3 species that are primary parasites in humans and many others that have demonstrated zoonotic potential. Incomplete knowledge of taxonomy and species- level relationships hinders development of a comprehensive understanding of patterns of host use, and the potential for disease. We completed the first phylogenetic study for species of Taenia, providing novel information that will enhance our ability to predict and understand life history and geographic distribution. Based on this analysis it is shown that rather than 12 genera only one should be represented for Taenia tapeworms. This will serve to clarify a long-standing controversy about the taxonomy of this economically critical parasite group. Further, it was demonstrated that the diversification for Taenia spp has been strongly influenced by host-switching among felids, canids and other carnivorous hosts including humans. The species that occur in humans are not closely related; T. saginata + T. asiatica are putative sister-species, only distantly related to T. solium. Phylogenetic information constitutes the framework for elucidating the distribution of Taenia in humans, domestic stock used as food resources, and the occurrence of zoonotic infections derived from other carnivores including canids and felids.
Cladistic analysis of a numerical data matrix describing 27 characters for species of Taenia resulted in 4 MPT's (174 steps; Cl=0.28; Hl=0.72; Rl=).48). Monophyly for Taenia is diagnosed by the metacestode which is either a cysticercus or a form derived from a bladder-like larva. The genus is further diagnosed by a series of ambiguous synapomorphies that are influenced by homoplasy within the genus; 22 characters exhibited Cl's substantially less than 0.50, indicative of extensive plasticity for structural and ontogenetic attributes of Taenia spp. Tree structure provides no support for recognition of a diversity of tribes or genera within the subfamily Taeniinae: Fibriotaenini and Taenini have no phylogenetic basis. The genera Hydatigera, Fimbriotaenia, Fossor, Monordotaenia, Multiceps, Taeniarhynchus, Tetratirotaenia must be subsumed within Taenia, as they do not represent discrete monophyletic taxa. Coevolution with respect to carnivorous definitive hosts and Taenia appears to be limited. Although felids are putative ancestral hosts, contemporary associations appear to have resulted from extensive host- switching among felids, canids, hyaeniids and others. In contrast, relationships with herbivorous intermediate hosts are indicative of more pervasive convolution; rodents as intermediate hosts are postulated as ancestral for the Taeniidae, Taenia plus Echinococcus. Patterns appear consistent with rapid shifts between phylogenetically unrelated carnivores.