Phylogeny of species of the genus Litomosoides (Nematatoda : Onchocercidae): Evidence of rampant host switching

Filarioid nematodes of the genus Litomosoides occur in the abdominal and (o r) thoracic cavities of marsupials, rodents, and bats of the Nearctic and N eotropical regions. In this study, the phylogenetic relationships among the se nematodes were estimated with a parsimony analysis of morphological char acters derived from species descriptions. This nonweighted analysis produce d 20 shortest trees. The monophyly of the genus was not supported in that L itomosoides thomomydis and Litomosoides westi failed to group with the othe r members of the genus. When these 2 taxa (parasites of pocket gophers) wer e excluded, monophyly of Litomosoides was supported by 2 synapomorphies (st ructure of the walls and general shape of the stoma); however, ancestor-des cendant relationships among the species in the genus were not well resolved . A posteriori reweighting of the characters produced a single tree, differ ent from all 20 most parsimonious trees. Alternative host-parasite evolutio nary models were tested against these results supporting the process of hos t switching as being most important in forming the patterns of mammal-nemat ode associations that have been detected in this group of nematodes.