New Paper: Parasite life cycles and mariculture

I got my start in an aquaculture-related field, although it was culturing endangered aquatic species rather than commercial ones. Over the last five years I've had the opportunity to explore another passion of mine - the complex life cycles of marine parasites. Well, in one of my recently released papers, I got to do a pretty nice mashup of those two concepts:

Huston, D.C., Ogawa, K., Shirakashi, S. & Nowak, B.F. 2020. Metazoan Parasite life cycles: significance for fish mariculure. Trends in Parasitology. DOI:https://doi.org/10.1016/j.pt.2020.07.011

Aquaculture is expanding rapidly offshore into the sea and open oceans (aka mariculture). One of the most popular methods being employed by the finfish industry is the use of suspended cages or net pens moored offshore which allow constant water exchange for the farmed fish. This seems to be working great for a lot of reasons, but it does allow parasites to rather easily enter the net pens. 

In our paper we discuss how a renewed focus on basic parasite biology, especially life-cycle characteristics, can be used to manage parasitic infection in net-pen mariculture without the use of chemical treatment. We hope that our paper will renew interest in understanding basic aspects of marine parasite life-histories and promote research focused on elucidating parasite life cycles.

Phylogenetic evidence for a new Acanthocephalan family?

Phylogenetic evidence for a new Acanthocephalan family?

In my previous paper on acanthocephalans we proposed a new family (the Pyriproboscidae) based on phylogenetic evidence. In a follow up article, Lesley and I argue for the recognition of a new genus and another new family, Spinulacorpus and the Spinulacorpidae, respectively.

Huston, D.C. and Smales, L.R. 2020. Proposal of Spinulacorpus biforme (Smales, 2014) n. g., n. comb. and the Spinulacorpidae n. fam. to resolve paraphyly of the acanthocephalan family Rhadinorhynchidae Lühe, 1912. Systematic Parasitology. https://doi.org/10.1007/s11230-020-09923-7

One of the things we observed in our previous project was the species Rhadinorhynchus biformis Smales, 2014, resolved basal to the families Rhadinorhynchidae + Transvenidae, resulting in a paraphyletic Rhadinorhynchidae. In the original description, Smales (2014) noted that the trunk spine pattern in R. biformis was unlike any other species described in the genus. So it seemed like we had phylogenetic and potentially morphological evidence that R. biformis didn’t truly belong in the Rhadinorhynchidae (so long as we continue to consider the Transvenidae as distinct from the Rhadinorhynchidae). We didn’t have enough specimens at the time of our first paper to get into this particular problem, but later we examined additional specimens and did some far more intensive phylogenetic analyses. Overall, we found sufficient evidence to consider R. biformis as distinct from the Rhadinorhynchidae, and thus proposed our new genus and family.

Our aim with this paper was to help bring the Rhadinorhynchidae towards a modern classification scheme based on integrated molecular and morphological data. We think we’ve done this, but I suspect that there is much left to do. The Acanthocephala as a whole just keeps throwing up surprises and morphology and molecules seem to clash in the Acanthocephala much more than the other groups I have worked on.

 

New Paper: Acanthocephalans from Australian Marine Fish

I've got a new paper out, this time on Acanthocephalans. This was one of those projects that started off simple and then snowballed into a serious undertaking.

D.C. Huston . T.H. Cribb and L.R. Smales. 2020. Molecular characterisation of acanthocephalans from Australian marine teleosts: proposal of a new family, synonymy of another and transfer of taxa between orders. Systematic Parasitology.
https://doi.org/10.1007/s11230-019-09896-2

Acanthocephalans are a strange group of obligate endoparasites. Generally, they have two-host life cycles, with an invertebrate intermediate and vertebrate definitive host. Despite being worm-like and traditionally lumped in with the parasitic 'helminths', molecular phylogenetic study has demonstrated that acanthocephalans are most closely related to the rotifers. A most curious evolutionary trajectory for an ancient rotifer-like beast.

A lot of the specimens I was after for my PhD research came from species of an unusual family of fishes, the Kyphosidae. Well, many of the kyphosids I found had heavy infections of acanthocephalans. This project began because I wanted to identify them. Next thing I knew I was taking all the acanthocephalans from the Marine Parasitology Lab at The University of Queensland to the South Australian Museum to work with Dr Lesley Smales identifying them. I noticed that, at that time, there weren't any molecular sequences available for any Australian acanthocephalan. Thus I started sequencing all the species in my collection. This took years - I was doing this work as a side-project to my PhD on digenetic trematodes, and more and more acanthocephalan specimens kept getting added as the years wore on. It was worth it in the end - we got some interesting phylogeny results which led us to do some much needed taxonomic revisions and we even got to propose a new family.

Publishing this paper also allowed me to experience the joys of making a mistake in something I've put out on public record. Well, I say mistake, but really it was mistakes... I requested a correction shortly after some things were brought to my attention - and its just come out (https://doi.org/10.1007/s11230-019-09896-2.) Somehow a couple typos made it all the way through drafting, revision and peer review. You would think that after reading through a draft you've been writing 10-20+ times you would notice these things, but I guess sometimes its easy to glaze over as you go, especially when reading over convoluted scientific names (note to self - always add scientific names to the word processor dictionary). 

As if that wasn't enough, I found myself greatly embarrassed when another researcher let me know that two of the cox1 sequences I uploaded to GenBank were coming up in odd places in the phylogeny they were building. Well, I double checked them and sure enough they were contaminated with DNA from other acanthocephalans from the same sequencing batch. I immediately contacted GenBank and had them flag those sequences - so they are no longer available for download. This problem seems to be a result of a labeling error in the spreadsheet I was using to track the sequences as I generated them over the many years of the project. I provided the cox1 sequences as part of the project, but didn't actually do anything with them for the paper, so I didn't notice their odd phylogentic positions myself. (second note to self - always double check each sequence via a quick tree and BLAST before uploading). All the analyses in the paper used only 18S and/or 28S sequences. Anyway, embarrassing, but at least the error didn't impact any of the results of the study...! So overall a bit of a lesson to self. It is easy to make silly mistakes even with a doctorate and huge amounts of experience writing and doing science. Accepting mistakes and making corrections is part of the scientific endeavor - transparency and honesty are key. I've heard it said somewhere, in discussions on corrections to scientific works: 'to err is human, to correct divine' !

New Paper on digenean cercariae (Pronocephaloidea)

It was studying snails infected with digeneans that sparked my interest in the group originally, so I'll always have a soft spot for projects working on digenean cercariae. A recent paper that has come out of the Marine Parasitology Laboratory at the University of Queensland (with me as a co-author) characterizes a number of cercariae which belong to a interesting digenean lineage, marine species of which parasitise the respiratory and alimentary tracts of birds, turtles and mammals.

T.H. Cribb, P.A. Chapman, S.C. Cutmore and D.C. Huston. 2020. Pronocephaloid cercariae (Platyhelminthes: Trematoda) from gastropods of the Queensland coast, Australia. The Journal of Helminthology. https://doi.org/10.1017/S0022149X19000981

We described five new pronocephaloid cercariae and provided molecular sequences for each species. We suspect that these species are parasites of marine turtles or perhaps mammals (dugongs), as none of them were found in a clade with the major family of bird parasites of this lineage (Notocotylidae). There are almost no molecular resources for adult pronocephaloids from turtles, so unsurprisingly we did not get a match for any of our cercariae with an adult. Marine turtles are, and will likely continue to be, under threat and are protected in Australia - so I don't foresee a large, modern, molecular-grade collection of pronocephaloids from marine turtles becoming available for study any time soon (and that's probably a good thing). Thus, collections from gastropods represent a great molecular resource for expanding the pronocephaloid phylogeny.

Worms living within worms: a new endosymbiotic rhabdocoel flatworm (Umagillidae)

Describing new species of obscure invertebrates is how I get my kicks, thus I'm quite pleased with one of my most recent papers.

Huston, D.C. 2019. Collastoma esotericum (Neodalyellida: Umagillidae), a new species of sipunculan-inhabiting rhabdocoel from Queensland, Australia. Zootaxa, 4701 (6), 563-573.

http://dx.doi.org/10.11646/zootaxa.4701.6.5 

The most well-known parasitic flatworms are the highly-derived monogeneans, digeneans and cestodes, members of the platyhelminth subclade Neodermata. However, there are numerous ecto- and endosymbiotic ‘turbellarian’ flatworms scattered throughout the remaining lineages of the Platyhelminthes.

Invertebrates host a variety of endosymbiotic flatworms and these relationships are likely among the most ancient of metazoan symbioses. Echinoderms host two distinct groups of endosymbiotic flatworms, species of the families Umagillidae and Pterastericolidae. The pattern of host-association is also peculiar. The crinoid, echinoid and holothuroids host umagillids, while the asteroids host pterastericolids. There is apparently no overlap. Further, some umagillids have been reported from species of the Sipuncula (peanut-worms). The overall patterns suggests (to me at least!) multiple transitions from free-living to endoparasitism. However, none of these flatworm lineages have been studied in great detail, and there are few molecular resources for these species.

In my MS I describe a new species of the peanut-worm inhabiting umagillids. I was hoping that my molecular analyses would provide strong evidence for my above hypothesis (multiple transitions from free-living to endoparasitism), however I was only able to obtain sequences of the 18S rDNA gene as amplification of all other regions failed, despite the many different primers and cycling conditions I tried. Ultimately the results of my analyses didn't provide enough support to show this for sure just yet, but I suspect that future work will.

New paper on the Digenean family Enenteridae

A recent-ish paper of mine was the culmination of around 3 years of work (so most of my PhD)

2019. DC Huston, SC Cutmore, TH Cribb. An identity crisis in the Indo-Pacific: molecular exploration of the genus Koseiria (Digenea: Enenteridae). International Journal for Parasitology 49 (12), 945-961.
https://doi.org/10.1016/j.ijpara.2019.07.001

Much of my PhD focussed on the parasites of a unique group of herbivorous marine fishes, species of the family Kyphosidae (the drummers or sea-chubs). These fish are remarkable in that they eat almost entirely algae, and have lots of endosymbiotic organisms which help them with hindgut fermentation. Microbial fermentation has been poorly studied in fish, but I suspect it may have something to do with the unique parasite fauna of such fish species.

Anyway, the family Enenteridae needs a lot of work, and the genus Koseiria was a natural first choice to start the process. It turned out to be a quite complicated and challenging project, but resulted in a good paper, with a new genus, three new species and some new combinations. Next project for the family Enenteridae is the major lineage (the genus Enenterum)!