A paedomorphic parasite associated with a neotenic amphibian host: Phylogenetic evidence suggests a revised systematic position for Sphyranuridae within anuran and turtle Polystomatoineans

The phylogenetic relationships of the families Polystomatidae and Sphyranur idae (subclass Polystomatoinea) within tetrapod monogenean parasites were i nvestigated using partial 1.8S rDNA sequences. About 600 nucleotides of 11 species were sequenced, including 7 species of the most common subfamilies of Polystomatidae found in anurans and turtles, 1 species of the family Sph yranuridae parasitizing exclusively urodelans, and 3 species of the subclas s Oligonchoinea infesting teleostean fishes. The phylogenetic analyses were performed using three reconstruction methods: neighbor;joining, maximum-pa rsimony, and maximum-likelihood. Polystomatoineans but not polystomatids we re shown to be monophyletic, Within the polystomatoineans there are two cla des: one includes the amphibian monogeneans (anuran polystomatids and urode lan sphyranurids) and the other includes the turtle polystomatids, Polystom atoineans may have coevolved with amphibian hosts, and an ancestral "polyst ome" dispersed at least 200 million years ago, either from the basal stem o f lissamphibians or from an anuran ancestral stock, to freshwater turtles. Furthermore, the urodelan genus Sphyranura, initially assigned to the famil y Sphyranuridae on the basis of morphological and ontogenetic evidence, is clearly nested within polystomatids, suggesting that its systematic status must be revised. This supports recent findings which argue that species of the family Sphyranuridae may be paedomorphic parasites exclusively infestin g neotenic mudpuppies. (C) 2001 Academic Press.