Frying pans, mullets and squelchers
22 November 2010
One of the goals of the CReefs Australia project is to build capacity in the field of taxonomy in Australia – and the next generation of parasitologists are benefitting from this commitment first hand.
Three University of Queensland honours students – Vivian Geow, Nancy Trieu and Jon McDougall – are participating in the CReefs field expedition to Heron Island under the watchful eye of their supervisor, Associate Professor Tom Cribb. They are each aiming to measure the biodiversity of certain groups of parasitic worms in host fishes found on reefs in the area.
Vivian is targeting parasites of the genus Xystretrum of the family Gorgoderidae, found in the urinary bladders of ray-finned fishes of the order Tetraodontiformes, which includes triggerfishes, file fishes and puffer fishes.
Very little work has been done on these parasites: the existing taxonomy has just 11 species described, most recently from the 1970s, so no DNA analysis has ever been done," Vivian explains.
"So far on this field trip, I have found several fish infected with this parasite. I can identify the parasite to family – the Xystretrum have a distinct, frying pan shape, with a round body and an elongated front end – and when I conduct more sophisticated analyses back in the lab, I hope to be able to tell what species they are and how different they are from each other," she says.
Nancy, meanwhile, is interested in exploring host-specificity and potential species complexes of parasites of the family Bivesiculidae found in the intestines of a range of fishes.
"Parasitic worms are increasingly found to be strictly host-specific: each species of parasite is found only in one species, or in a few closely-related species, of fish. One species of the parasites I'm targeting, however, have been found in mullets and blennies, which do not even belong to the same order of fishes," Nancy explains.
"This leads us to suspect that some of these parasites may in fact be, not one species, but a species complex: a group of very closely-related species in which the differences between species are not yet understood," she says.
She will study the morphology (the study of the shapes, structure and anatomy) and molecular biology (DNA analyses) of the specimens she collects here with the intention of resolving the relationships among the parasites and between the parasites and their hosts.
Jon's area of focus is intestinal flukes from the genus Hexangium in the family Microscaphidiidae, found in the fish families Siganidae and Acanthuridae, commonly known as rabbitfish and surgeonfish.
He will use morphological and molecular analysis to determine whether there is a species complex (multiple species within a host) present in each of the two host families. He is also interested in the parasites' morphological and behavioural characteristics, and how unique characteristics can be used to delineate species.
"Most trematodes have an oral sucker and a ventral sucker, which they use to attach to the host – but the parasites I am targeting have neither. We believe they may be able to use part of their body to create a concave surface that acts as a pseudo-sucker, and attach to the host's intestinal wall that way," Jon explains.
"As well, many of these parasites move in unusual ways: some of them squelch along by some form of peristaltic movement; others will sit and wiggle, but do not move much from one spot, generally due to their ventral sucker anchoring them in place.
"I think the method of movement is quite important in distinguishing between the species, as well as colour, size, shape and the internal structures," he says.
Based on the specimens the students collect this month, they expect to be able to confirm which known species are present at Heron, to discover new species, and to refine the existing taxonomies. They hope to contribute to better understanding of the biogeography, host-parasite relationships and life cycles of the parasites they are studying.