RELATIVE MERITS OF NUCLEAR RIBOSOMAL INTERNAL TRANSCRIBED SPACERS ANDMITOCHONDRIAL CO1 AND ND1 GENES FOR DISTINGUISHING AMONG ECHINOSTOMA SPECIES (TREMATODA)

Cryptic species, belonging to the 37 collar-spine Echinostoma group, w ere distinguished using nuclear rDNA ITS (884 bases) and mtDNA CO1 (25 7 bases) and ND1 (530 bases) sequences. Sequences were obtained from f ive 37 collar-spine species, Echinostoma trivolvis, E. paraensei, E. c aproni, E. revolutum and E. sp.I, a parthenogenetic isolate from Afric a. Three geographic isolates of E. caproni were compared. Average sequ ence divergence among the 37 collar-spine species range from 2.2 % in the rDNA ITS through 8 % for the CO1 and 14% for the ND1. In addition, genes were sequenced from 2 non 37 collar-spine species, E. hortense and an undescribed Australian species, E. sp. (Aus). For each gene, di stances of terminals from a predicted ancestral sequence were calculat ed. These indicated that ND1 is diverging significantly faster than th e other 2 regions. In the CO1 gene most substitutions are synonymous a nd saturation has been reached for the majority of pairwise comparison s. The ND1 gene exhibits greater pairwise divergence but less evidence of saturation due to weaker conservation of first and second codon po sitions. The ITS has no amino acid coding constraints and displays no evidence of saturation. Although all 3 regions successfully distinguis hed the nominal species, ND1 appears to be the most informative region for investigating relationships within the 37 collar-spine group.