PHYLOGENETIC-RELATIONSHIPS OF THE FAMILY CAMPULIDAE (TREMATODA) BASEDON 18S RIBOSOMAL-RNA SEQUENCES

Traditionally, the family Campulidae has been associated either with t he family Fasciolidae, parasites of ruminants, or the Acanthocolpidae, parasites of fishes, based on morphological similarities. Since morph ology does not seem to resolve clearly the problem of the relationship s of campulids, we have used the sequences of the 18S rRNA gene of the campulids Zalophotrema hepaticum, Campula oblonga and Nasitrema globi cephalae, the fasciolid Fasciola hepatica, the acanthocolpid Stephanos tomum baccatum and the outgroup Schistosoma mansoni to infer a phyloge ny. Maximum parsimony and neighbour-joining methods were applied. Both methods indicated that campulids are closer to acanthocolpids than fa sciolids. In order to confirm this relationship, we generated a second phylogeny using all the partial sequences of the 18S published for tr ematodes: Lobatostoma manteri, Echinostoma caproni, Calicophoron calic ophorum, Tetracerasta blepta, Gyliauchen sp. and Opistorchis viverrini , plus those mentioned above, and Dicrocoelium dendriticum. The aspido gastrean L. manteri was used as the outgroup. Results were identical t o the first analysis. According to this and the most recent Digenean p hylogeny, which considers campulids and acanthocolpids as sister group s, we suggest that a common origin for these 2 groups would imply a ho st-switching process. The life-cycle of acanthocolpids includes marine gastropods as first intermediate hosts, and fishes as second intermed iate and definitive hosts. In this context, the hypothesis would be th at trematodes whose cycle ended in fishes were able to switch to mamma lian hosts.