A molecular phylogeny of the genus Ichthyocotylurus (Digenea, Strigeidae)

Three nucleotide data sets, two nuclear (ribosomal internal transcribed spa cer regions 1 and 2, ITS1 and ITS2) and one mitochondrial (cytochrome c oxi dase subunit 1, CO1), were analysed using distance matrix and maximum likel ihood methods to determine the interrelationships amongst the four species attributed to the genus Ichthyocotylurus Odening, 1969. Sequence data obtai ned from all gene loci investigated supported the position of Ichthyocotylu rus variegatus as a species discrete from Ichthyocotylurus platycephalus. P hylogenetic analyses yielded congruent trees, with I. variegatus isolates c omprising a common clade to which I. p(platycephalus constitutes a sister t axon. Ichthyocotylurus erraticus and Ichthyocotylurus pileatus were found t o demonstrate a similarly close inter-specific relationship. The greatest i ntra-generic divergence occurred in the CO1 region (16% variability), with resultant disparities in three to eight encoded amino acids. PCR amplificat ion yielded multiple ITS 1 products for all Ichthyocotylurus spp. Analyses of equivalent-sized amplicons showed 5.4% intrageneric variation and severa l point mutations between I. variegatus isolates from different geographica l localities and from different piscine hosts. The ITS? locus was extremely conserved, with less than 1% variation between species. No intra-specific variation was recorded for any CO1 or ITS?, sequences. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.