"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

July 24, 2012

Special Report: #ASP2012 (Australia) Part IV: Swimming with the Parasites

This post is part 4 (and final) of my special report on the #ASP2012 (Australia) meeting at Launceston, Tasmania - see part 1 here, part 2 here, and part 3 here.

Photo by Kate Hutson
The last day of the conference was a bumper day for marine parasitology so I will just write as briefly as I can on what I saw to cover some highlights. The day kicked off with a series of plenary lectures on; sea lice on farmed salmonids in British Columbia, the history of using parasites as biological markers to identify stock and age of orange roughy (Hoplostethus atlanticus), and an overview of the various parasitic infections that pose a threat to aquaculture by Prof. Barbara Nowak.

But out of those, the presentation which stood out as being most relevant to the original mission of this blog was a talk by Terry Miller - a research officer from the Queensland Museum. He discussed the outcome (so far) of a project to explore to categorise the diversity and genetics of parasites found in fishes of Lizard Island and Heron Island on the Great Barrier Reef, as well as Ningaloo Reef on Western Australia as a part of the Census of Marine Life project. The sheer biodiversity of parasites was the reason why this blog was started and a subject that we discussed in an essay at the end of 2010 - Terry Miller, with his many collaborators, have certainly been busy finding, describing, and classifying this overlooked wealth of biodiversity. They found all manners of myxozoans, flukes, tapeworms, and roundworms, and have already described 56 new species so far. But there are still many unanswered questions relating to biogeography, life-cycles, phylogenetics of these parasites and their significance for fisheries. With 2000 species of parasitic flukes (not counting other fish parasites) estimated to be in the fishes of Australia alone - that's a lot of species descriptions to come!

Photos and drawings used with permission from Leonie Barnett
Speaking of the weird and wonderful, Leonie Barnett from Central Queensland University presented a poster on the molecular phylogeny of a family of parasitic flukes call acanthocolpids which have very odd-looking and remarkably ornate cercariae (the free-living stage which emerge form the first host in the fluke life-cycle). Most cercariae simply look like microscopic tadpoles, with a leaf-shaped body followed by a tapered tail. Leonie has given those acanthocolpid "funky cercariae" nicknames such as "Ducks" and "Starship Enterprise"(see photo on the right). The question must be asked (which at this point can only be rhetorical) - why produce such remarkably elaborate-looking larvae when the majority of them will die after a day or two? What hosts do these parasites infect which warrant such amazing extravagance?

There were a number of presentations thorough the day which were relevant to the fisheries and aquaculture industry, including talks on the detection and treatment of blood-flukes in ranched tuna, identifying and characterising anisakid nematode larvae (which normally infect marine mammals but can cause disease in human if accidentally ingested) from fishes in Australasian waters, and a presentation by Kate Hutson on assessing risks pose to barramundi and mulloway aquaculture by various parasites.

Different Philophthalmus sp. rediae morphs
(insert: specialised morph attacking
the sporocysts of a rival species)
Ian Whittington started off the afternoon session with some videos of monogeneans and to follow that, I talked about potential caste formation and eusocial-like traits amongst the asexual stage of Philophthalmus sp. and how these specialised morphs may in fact be playing a in interspecific competition (see photo on the right or my alternative rendering here)

Sarah Catalano from the Hutson lab talked about a bizarre and little-known group of parasite called the dicyemids which are found in the kidneys of cephalopods (octopus, squid, cuttlefish). These parasites have a very simple body structure, but a very complicated life-cycle. They are astonishingly diverse and also display high levels of host specificity with each species occurs exclusively in a single host species. Because of their specificity they can also be used as a biological marker to reveal different host species where before they were simply considered as subpopulations.

Also from the Hutson lab was Alex Brazenor who presented a study looking at the effects of different water temperature and salinity levels on Neobenedenia - the little worm mentioned in the previous post which is capable of consecutive bouts of self-fertilisation and kick off an outbreak on its own. Alex found that at higher water temperature, Neobendenia lived a faster life -  whereas it took 18 days to reach sexual maturity at 22°C, it only took 10 days to reached that stage at 30°C. Their eggs are more likely to hatch successfully at the higher temperature and salinity level, although if the temperature reached beyond 32°C they start suffering detrimental effects.

Well, that does it for my reports on the #ASP2012 (Australia) conference. Overall, I had a great time - I got to catch up with some colleagues I haven't seen for a while,we talked about a lot of interesting science, and I saw some great presentations and posters - just about all that you can ask for at a conference really. So for me, it's back to writing up blog posts about new papers being published on all manners of interesting parasites - and I already have quite a few lined up...


  1. An entire phylum that only contains octopus kidney parasites? Is it common for such a broad category of organism to have such a small niche. I guess if it works, stick to it.

  2. I know, isn't it cool? And like you said, it obviously worked out well for that group. I really look forward to seeing any future findings by Sarah Catalano on this peculiar group of organism.

    I don't think it can be considered as a "common" phenomenon, but I suppose if the host group is diverse enough, the parasite/symbiont can also become really diverse even if they only occupy a very specific niche - actually, feather lice comes to mind - not only are they very specific about the host species they infect, but also what particular *type of feathers* on that host which they cling to.

  3. Yayyyy dicyemids! They're my favorite. I co-authored the dicyemid chapter in Light's Manual with Eric Hochberg a number of years ago, and really wanted to study them in grad school, but my NSF proposal got an honorable mention (=$0). I'm delighted to hear that Ms. Catalano is working on them and can't wait to see what she discovers!

    To address notElon's question, one of the reasons that dicyemids are in their own phylum is that no one has been able to figure out to whom they're most closely related. Their anatomy is so incredibly simple--just a handful of cells--that they were once considered "mesozoa," a middle step between single-celled protozoa and multicellular metazoa (animals). But now it's thought that they may once have been more complex, perhaps even a kind of flatworm that simplified over time, as many highly specialized parasites tend to do (I'm sure there are some great posts on this blog about that phenomenon: simplified bodies, complicated life cycles). So it's possible that someday the group will become embedded within another phylum, as a highly derived lineage.

    But for my part, I kind of hope they retain phylum status. =)