Genetic variation was examined in the anoplocephalid cestode Progamotaenia festiva, from Australian marsupials, in order to test the hypothesis that P. festiva, is a complex of sibling species and to assess the extent of host switching reported previously based on multilocus enzyme electrophoresis (MEE). Polymerase chain reaction (PCR)-based single-strand conformational polymorphism (SSCP) was used for the analysis of sequence variation in the cytochrome c oxidase subunit 1 (cox1) gene among 179 specimens of P. festiva (identified based on morphology and predilection site in the host) from 13 different host species, followed by selective DNA sequencing. Fifty-three distinct sequence types (haplotypes) representing all specimens were defined. Phylogenetic analyses of these sequence data (utilizing maximum parsimony and neighbour-joining methods) revealed 12 distinct clades. Other heterologous species, P. ewersi and P. macropodis, were used as outgroups and the remaining bile-duct inhabiting species, P. diaphana and P. effigia, were included in the analysis for comparative purposes. The latter 2 species were nested within the clades representing P. festiva. Most clades of P. festiva identified were restricted to a single host species; one clade primarily in Macropus robustus was also found in the related host species M. antilopinus in an area of host sympatry; another clade occurring primarily in M. robustus occurred also in additional kangaroo species, M. rufus and M. dorsalis. High levels of genetic divergence, the existence of distinct clades and their occurrence in sympatry provide support for the hypothesis that P. festiva represents a complex of numerous species, most of which, but not all, are host specific. Three distinct clades of cestodes were found within a single host, M. robustus, but there was no evidence of within-host speciation.

Sequence variation within 3 morphologically defined species of the anoplocephalid cestode genus Progamotaenia (P. ewersi, P. macropodis and P. zschokkei) was investigated using the cytochrome c oxidase subunit 1 gene. The magnitude of genetic variation detected within each morphospecies suggests that, in each instance, several cryptic species are present. Within P. ewersi, 5 genetically distict groups of cestodes were detected, 1 shared by Macropus robustus and M. parryi in Queensland, 1 in M. agilis from Queensland, 1 in Petrogale assimilis from Queensland, 1 in Macropus fuliginosus from South Australia and 1 in Wallabia bicolor from Victoria. In P. macropodis, cestodes from M. robustus from Queensland, Western Australia and the Northern Territory, M. parryi from Queensland and M. eugenii from South Australia were genetically distinct from those in Wallabia bicolor from Queensland and Victoria and from M. fuliginosus from South Australia. P. zschokkei consisted of a number of genetically distinct groups of cestodes, 1 in Lagorchestes conspicillatus and L. hirsutus from Queensland and the Northern Territory respectively, 1 in Petrogale herberti, P. assimilis and M. dorsalis from Queensland, 1 in Onychogalea fraenata from Queensland, 1 in M. agilis from Queensland and 1 in Thylogale stigmatica and T. thetis from Queensland. In general, genetic groups within each morphospecies were host specific and occurred predominantly in a particular macropodid host clade. Comparison of genetic relationships of cestodes with the phylogeny of their hosts revealed examples of colonization (P. zschokkei in M. agilis) and of host switching (P. zschokkei in M. dorsalis).