Phylogeny of Taenia: Species definitions and origins of human parasites

Abstract

Phylogeny is fundamental as it constrains explanations about history and forms our foundation for recognizing and diagnosing species. In the absence of such a framework taxonomists historically relied on intuitive processes, personal judgment and authority, often embracing a typological view of species that disregarded otherwise unequivocal historical and biological criteria. Species of Taenia are among the most characteristic tapeworms infecting carnivores and humans as definitive hosts and indeed Taeniidae is unique among the Eucestoda in requiring 2 obligate mammalian hosts for transmission; a high percentage (> 80%) of life cycles have been completely elucidated among the approximately 45 species and nominal subspecies of Taenia. Until recently there had been no comprehensive attempts at reconstruction of a phylogeny among these important parasites. Such analyses have allowed us to explore the origins and evolution of those independent species of Taenia that occur in humans (T. saginata, T. asiatica, and T. solium) and to understand the ecological and historical processes serving as determinants of biogeography and hostassociation. These studies supported the status of T. asiatica as a valid species and diagnosed a relationship as the sister-species of T. saginata. These conclusions contrasted with a diversity of opinions that would subsume T. asiatica as a subspecies. Recognition of a species constitutes a specific and testable hypothesis, is not an arbitrary decision and is most appropriately assessed in the context of phylogenetic or historical data. Considering macrospecies, a process has been outlined by Brooks and McLennan [Brooks DR, McLennan DA. The nature of diversity: an evolutionary voyage of discovery. University of Chicago Press: Chicago; 2002] as follows: (1) Discovery: a systematist describes the species; (2) Phylogenetic reconstruction; (3) Evaluation I: do sister-species show geographical overlap-are they sympatric or allopatric (use phylogeny + geographical distributions)? (4) Evaluation II: are sister-species reproductively isolated based on information from natural history, ecology and reproductive biology? Species may be viewed in the context of microevolutionary and macroevolutionary processes. For instance, microspecies are defined in ecological time and involve populations and contemporary process that are potentially reversible (reticulate). In contrast, macrospecies as exemplified by T. saginata and T. asiatica are divergent lineages resulting from processes in evolutionary time where an ancestor has undergone a permanent split that is non-reversible (non-reticulate). Applying these criteria in evaluation of T. saginata and T. asiatica, it becomes clear that in evolutionary time these represent historical lineages with independent spatial and temporal trajectories, having separated from a common ancestor near 0.78 to 1.71 MYBP in Africa, or Eurasia. In ecological time, sympatry, reproductive isolation, and differences in life history evident for T. saginata and T. asiatica a...

Characterization of Taenia madoquae and Taenia regis from carnivores in Kenya using genetic markers in nuclear and mitochondrial DNA, and their relationships with other selected taeniids

“…It is intriguing and unexpected that T. madoquae, a species with a cysticercus in the skeletal muscles of a small antelope appears to be genetically closely related (of the species studied here) to T. serialis and T. multiceps, both of which have a coenurus as the larval stage. Current findings contrast with cladistic analyses by Hoberg et al [37], [38] and [39], which indicated that T. madoquae appeared in a subclade separate from both T. multiceps and T.…”

“…This finding is similar to the cladistic study by Hoberg et al [37], [38] and [39], in which they both appeared in the same subclade. Both species have a relatively large cysticercus (usually up to 2.0-2.5 cm in the case of T. regis, and 2.5-4 cm or more for T. hydatigena) in the serosa in the coelom of the intermediate host, but they are clearly distinct based on adult morphology.…”

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

“…These biogeographic scenarios are all plausible with respect to the putative timing of species splitting events (Figure 4) and they can be related to the taxon pulse theory, whereby cyclical episodes of isolation and range expansion create opportunities for a complex interplay of cospeciation, host switching and coadaptation (Hoberg andBrooks, 2008, 2010). However, they are all essentially historical narratives, which have not yet been tested empirically.…”

“…Accurate delimitation of species provides the foundation of our knowledge of parasite life history, distribution and disease processes (Hoberg, 2006). In addition, controversy and instability in species names can have important public health implications.…”

First Record of Alcataenia larina larina (Cestoda: Dilepididae) in Atlantic Puffins (Aves, Alcidae, Fratercula arctica) from Newfoundland, Canada

“…This led to the erection of the subspecies Alcataenia larina pacifica Hoberg, 1984 from the North Pacific and Alcataenia larina larina from the North Atlantic based on differences in the dimensions of cirrus sac, number of testes, as well as variations in the other morphological characters (Hoberg 1984). These putative subspecies represent independent sister-lineages that are disjunct and geographically isolated, and as such, justification may exist to elevate these to the status of separate species (Hoberg, 1984(Hoberg, , 2006Hoberg, unpublished data); that decision is beyond the scope of the current study.…”