Phylogenetic analysis of the Monocotylidae (Monogenea) inferred from 28S rDNA sequences

The current classification of the Monocotylidae (Monogenea) is based on a p hylogeny generated from morphological characters. The present study tests t he morphological phylogenetic hypothesis using molecular methods. Sequences from domains C2 and D1 and the partial domains C1 and D2 from the 28S rDNA gene for 26 species of monocotylids from six of the seven subfamilies were used. Trees were generated using maximum parsimony, neighbour joining and maximum likelihood algorithms. The maximum parsimony tree, with branches sh owing less than 70% bootstrap support collapsed, had a topology identical t o that obtained using the maximum likelihood analysis. The neighbour joinin g tree, with branches showing less than 70% support collapsed. differed onl y in its placement of Heterocotyle capricornensis as the sister group to th e Decacotylinae clade. The molecular tree largely supports the subfamilies established using morphological characters. Differences are primarily how t he subfamilies are related to each other. The monophyly of the Calicotylina e and Merizocotylinae and their sister group relationship is supported by h igh bootstrap values in all three methods, but relationships within the Mer izocotylinae are unclear. Merizocotyle is paraphyletic and our data suggest that Mycteronastes and Thaumatocotyle, which were synonymized with Merizoc otyle after the morphological cladistic analysis, should perhaps be resurre cted as valid genera. The monophyly of the Monocotylinae and Decacotylinae is also supported by high bootstrap values. The Decacotylinae, which was co nsidered previously to be the sister group to the Calicotylinae plus Merizo cotylinae, is grouped in an unresolved polychotomy with the Monocotylinae a nd members of the Heterocotylinae. According to our molecular data, the Het erocotylinae is paraphyletic. Molecular data support a sister group relatio nship between Troglocephalus rhinobatidis and Neoheterocotyle rhinobatidis to the exclusion of the other species of Neoheterocotyle and recognition of Troglocephalus renders Neoheterocotyle,le paraphyletic. We propose Trogloc ephalus incertae sedis. An updated classification and full species list of the Monocotylidae is provided. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.