Co-evolutionary relationships between the nematode subfamily Cloacininae and its macropodid marsupial hosts

Morphologically based phylogenies of the cloacinine genera Cyclostrongylus, Macropostrongylus, Pharyngostrongylus, Popovastrongylus, Rugopharynx, Thal lostonema, Wallabinema, and Zoniolaimus were constructed and compared with the phylogeny of their respective macropodid hosts. These comparisons show some evidence of co-speciation. However, there was little consistency among trees of different nematode genera, parasite species were scattered amongs t hosts and basal parasite taxa were, in some instances, parasitic in hosts belonging to derived clades. A cladistic analysis, using as characters 208 cloacinine nematode species found in 23 species of host, produced a tree l argely resembling that of the host tree but with significant differences ex plainable by host switching among macropodids occupying similar habitat. Ne matodes were moderately host-specific, but some species occurred in three o r more distantly related host species indicating a degree of host switching . The results are more consistent with the hypothesis of a colonisation of macropodid hosts by cloacinine nematodes rather than a prolonged period of co-speciation although alternative interpretations of the data are also con sidered. (C) 2001 Australian Society for Parasitology Inc. Published by Els evier Science Ltd. All rights reserved.