UTILITY OF THE D1 DOMAIN OF NUCLEAR 28S RIBOSOMAL-RNA FOR PHYLOGENETIC INFERENCE IN THE DIGENEA

The relatively variable D1 domain near the 5' end of the 28S ribosomal RNA gene (large subunit rRNA) has been sequenced for 12 species of digenean trematodes. Phylogenetic relationships among these species and Schistosoma mansoni (previously published sequence) were investigated with maximum parsimony and distance methods. A DNA sequence from the tapeworm (Cestoda) Hymenolepis diminuta was used for outgroup comparison. In all analyses, several clusters of taxa appeared repeatedly: (1) four fasciolids; (2) three didymozoids with a hemiurid; and (3) two lepocreadiids with a gyliauchenid. Bootstrap resampling of the data revealed that the first two clusters were well supported. In contrast there was less support for the cluster containing the lepocreadiids and gyliauchenid. We conclude that the D1 domain is too variable for phylogenetic inference among distantly related families, but it is well suited to phylogenetic inference within and among closely related families in the Digenea.