Acanthurid fishes comprise one of the dominant groups of predominantly coral reef associated fishes. Acanthurids have a diverse and rich digenean fauna; there are now 139 gastro-intestinal digeneans recorded globally. I have identified 49 gastro-intestinal digenean species from 26 species and 746 individuals of acanthurids collected at five sites in the Indo-Pacific: Exmouth, Western Australia; Heron Island and Lizard Island, the Great Barrier Reef; Moorea, French Polynesia; and Moreton Bay, Brisbane, Queensland. This represents 35% of the world's recorded acanthurid digenean fauna. Ten new species are described from these fishes: Gyliauchenidae - Affecauda annulata Hall & Chambers, 1999*; Haploporidae - Hapladena machidai n. sp.; Lecithasteridae - Hysterolecitha ctenochaeti n. sp., H. queenslandensis n. sp., H. stysis n. sp., Quadrifoliovarium quattuordecim n. sp., Q. maceria n. sp., Q. simplex n. sp., Zebrasomatrema pichelinae Bray and Chambers, 2000*; Hemiuridae - Lecithocladium invasor Chambers, Carlisle, Dove and Cribb, 2001; Lepocreadiidae - Preptetos amitiense n. sp. and P. ancylophallos n. sp. In addition, the following species were redescribed from material collected in this study: Lecithasteridae - Bilacinia australis Manter, 1969, Quadrifoliovarium pritchardae Yamaguti, 1965, Unilacinia asymmetrica Manter, 1969; Hemiuridae - Lecithocladium chingi Manter and Pritchard, 1960. A further 16 species are recognised as new, but remain undescribed; drawings are provided of five species of undescribed haplosplanchnids. I also present 219 new host and locality records.
Molecular phylogenies based on ITS2 and 28S rDNA are presented for species of quadrifoliovariines, hysterolecithines, haplosplanchnids and Preptetos infecting acanthurids in the Indo-Pacific. Morphological characters of the Quadrifoliovariinae are mapped to a molecular phylogeny and possible avenues of character evolution and speciation are discussed. Molecular taxonomy was used to test morphological taxonomic groupings and suggests the presence of cryptic species within the morphotype of Preptetos caballeroi Pritchard, 1960. The data suggest that the size and shape of the cirrus-sac in species of Preptetos may be an informative morphological feature for systematic classification.
Recovery curves for digeneans from acanthurids suggest that a sample size of about 8-10 fishes of each host species is required to obtain a robust representation of the digenean fauna of a location, if most of the host species present at the location are sampled.
Host and parasite phylogenies were never found to be congruent and host-switching events appear to be common. The nature of the digenean fauna was found to be strongly associated with ecological characteristics of the host. Gastro-intestinal digeneans are therefore robust markers of host ecology. Fishes feeding on a diet of filamentous algae, macroalgae, detritus or zooplankton were each found to have a characteristic digenean fauna. The strength of this relationship allows inferences to be made about the host biology, by observations on their digenean fauna. Predictions may also be made on the likely digenean fauna of acanthurid species that have not been sampled, if details of their ecology are known.
Analysis of infection data within acanthurid species suggests that infections are largely stochastic events and that digenean longevity is short compared to that of their hosts. When the effect of phylogeny was controlled for by the use of independent contrasts, digenean richness across species was found to be significantly correlated with host size; larger hosts have a richer species fauna. Acanthurid species that feed on a broad range of dietary items are infected by a greater number of digenean species than those with narrow diets. Host species infected with a large number of digenean species are also likely to be infected by more digenean individuals.
The digenean fauna of acanthurids from Moorea, French Polynesia was found to be depauperate compared with that from sites on the Great Barrier Reef (Moorea had 13 observed and 15 estimated digenean species from six species of acanthurids, compared with 18 and 19 for Heron Island and 20 and 24 for Lizard Island). No increase in acanthurid digenean richness was found with decreasing latitude.
The pathology associated with a hemiurid, L. invasor, is described. This worm forms ulcerative, feeding nodules in the oesophagus of species of Naso at Heron Island. The possible function of such worm-induced pathology, in light of co-infection with a non-pathogenic hemiurid, is discussed.
* Description presented in accompanying literature, not in the body of the thesis.