Saturday, December 22, 2018

Exploring the dark food web? Start with molluscs first.


Parasites with complex life cycles, such as the ubiquitous digenetic trematodes, exploit different hosts for different reasons (i.e. asexual reproduction in a molluscan intermediate host and sexual reproduction in a vertebrate definitive host). At the same time, for transmission between different hosts, trematodes exploit trophic interactions between these hosts. Parasites with complex life cycles are hidden hitchhikers in food webs, creating an unseen web of interactions – what we might call the ‘dark food web’ (well, that’s what I like to call it because it sounds rad and you know, up with the times).


Parasites are consumers and constitute a large amount of biomass in communities (Kuris et al., 2008). There are a number of really great papers on the importance of incorporating parasites into food webs. For a start see Thompson et al. (2005), Lafferty et al. (2006, 2008) and the references within those papers. Furthermore, parasites are not only consumers, but are also predated upon (think gnathiid isopods and cleaner wrasse). Digenetic trematodes have a free-living larval stage, called a cercaria, which seeks to infect the next host in the digenean’s complex life-cycle. Cercariae are produced from asexual colonies residing in infected molluscs, and thousands of cercariae can emerge from an infected mollusc each day. In many communities a large proportion of the molluscs are infected with trematodes, so you can imagine that there are a lot of cercariae being pumped into the world’s ecosystems daily. This represents a huge, and mostly unstudied, path of energy flow in food webs (Thieltges et al. 2008; Morley, 2012).


Clearly incorporating parasites into food webs has great promise for understanding how complex ecological communities function. However, progress is generally hindered by a lack of knowledge of parasite life cycles. Most larval parasites are difficult to identify to species on the basis of morphology alone and in many cases these larval stages may only be identifiable to family (common for trematode cercaria). Thus traditional methods for elucidating life-cycles are slow and difficult. This process can be sped up significantly however, by using molecular barcodes to connect various life-cycle stages. I have done this twice previously (see this post and this post) – and in my recent(ish) paper I focused on molecularly characterising a whole community of trematodes parasitising a single species of gastropod on the Great Barrier Reef : 


Huston, D.C., Cutmore, S.C., and Cribb, T.H. 2018. Molecular systematics of the digenean community parasitising the cerithiid gastropod Clypeomorus batillariaeformis Habe & Kusage on the Great Barrier Reef. Parasitology international 67 (2018): 722735.


It took me over 3 years to collect all the data (mostly working on the side while I was on Heron Island for other reasons). Fortunately, I had a head start on this particular project because of the work of Cannon (1978), who had previously morphologically characterised most of the cercariae which I sequenced in my study. Although I didn’t find all the cercariae that Cannon (1978) described, I found two which he had not, showing a shift in the community structure over time. The new tally of digeneans which utilise Clypeomorus batillariaeformis on the Great Barrier Reef stands at 14! That is a large diversity and volume of cercariae being pumped into the waters of the Great Barrier Reef.


Although the morphology of the cercariae typically tell us what family they belong to, molecular data takes us a step further. Phylogenetic placements for cercariae can tell us what sorts of definitive hosts we ought to expect each cercariae ultimately aims to end up in, and from that we might infer what the transfer mechanisms might be. For example, in my study we found three species of the heterophyid genus Galactosomum. With that knowledge we know that the definitive hosts ought to be birds, and because all three of these species of Galactosomum had large, visually conspicuous cercariae we can infer that the second intermediate hosts are likely surface feeding fishes.


Characterising whole communities of digeneans from molluscs with molecules seems a great way to advance our understanding of food-web dynamics and build on our understanding of trematode-mollusc evolutionary interactions. Thus, when setting out to explore the dark food web, start with the snails first.



References


Cannon, L.R.G. (1978). Marine cercariae from the gastropod Cerithium moniliferum Kiener at Heron Island, Great Barrier Reef. Proceedings of the Royal Society of Queensland 89, 45–57.

Kuris, A.M., Hechinger, R.F., Shaw, J.C., Whitney, K.L., Aguirre-Macedo, L., Boch, C.A., Dobson, A.P., Dunham, E.J., Fredensborg, B.L., & Huspeni, T.C. (2008). Ecosystem energetic implications of parasite and free-living biomass in three estuaries. Nature 454, 515.

Lafferty, K.D., Allesina, S., Arim, M., Briggs, C.J., De Leo, G., Dobson, A.P., Dunne, J.A., Johnson, P.T.J., Kuris, A.M., & Marcogliese, D.J. (2008). Parasites in food webs: the ultimate missing links. Ecology letters 11, 533–546.

Lafferty, K.D., Dobson, A.P., & Kuris, A.M. (2006). Parasites dominate food web links. Proceedings of the National Academy of Sciences 103, 11211–11216.

Morley, N. (2012). Cercariae (Platyhelminthes: Trematoda) as neglected components of zooplankton communities in freshwater habitats. Hydrobiologia 691, 7-19.

Thieltges, D.W., de Montaudouin, X., Fredensborg, B., Jensen, K.T., Koprivnikar, J., & Poulin, R. (2008). Production of marine trematode cercariae: a potentially overlooked path of energy flow in benthic systems. Marine Ecology Progress Series 372, 147-155.

Thompson, R.M., Mouritsen, K.N., & Poulin, R. (2005). Importance of parasites and their life cycle characteristics in determining the structure of a large marine food web. Journal of Animal Ecology 74, 77-85.

Saturday, May 5, 2018

Isorchis cannoni n. sp. (Digenea: Atractotrematidae) from Great Barrier Reef rabbitfishes

This paper came out as an 'online-first-view' last year, and is still languishing in 'in press' purgatory, so I thought I would go ahead and do a quick write up. Here's the citation and link:

2018. Huston, D.C., Cutmore, S.C. and Cribb, T.H. Isorchis cannoni n. sp. (Digenea: Atractotrematidae) from Great Barrier Reef rabbitfishes and the molecular elucidation of its life cycle. The Journal of Helminthology (in press). PDF

This particular story begins with Dr. Lester Cannon’s study of the cerithiid gastropod Clypeomorus batillariaeformis (then called Cerithium moniliferum, a junior synonym) from Heron Island on Australia’s Great Barrier Reef. In his 1978 publication ‘Marine Cercariae from the Gastropod Cerithium moniliferum Keiner at Heron Island, Great Barrier Reef’ Cannon described 10 new trematode cercariae from C. batillariaeformis, and gave each cercariae a placeholder name and a numeral, e.g. Cercariae queenslandae I-X. The morphology of one of these cercariae (Cercaria queenslandae II) aligned closely with those known from the trematode family Haploporidae. In fact, Cannon noted that this cercariae might be that of Atractotrema sigani which was, at that time, considered a member of the Haploporidae, although today it is placed in the haploporid’s sister family Atractotrematidae. Atractotrema sigani parasitises rabbitfishes (family Siganidae), an important group of medium-sized, herbivorous marine fishes, several species of which feed on algae growing on the beachrock along Heron Island where C. batillariaeformis is found.

Cannon was about as close to the mark as one could get in those days, those days being those without molecular sequencing. In the past, elucidating life-cycles was rather difficult, and could only really be accomplished with captive populations and somewhat time-consuming experimental infections. Nowadays it is easy enough to generate molecular sequences from adult and larval trematodes and match them up!


Had molecular tools been available to Dr. Cannon, he would have quickly realised that the cercariae he had found were not those of A. sigani, and actually a species of atractotrematid yet to be discovered! This is what I found when I started a project sequencing the cercariae of C. batillariaeformis from Heron Island. When I began the project in 2015, the adult of Cercariae queenslandae II had not yet been discovered, but in 2017 we found the adults. Cannon was pretty close to the mark again: the definitive hosts turned out to be the same rabbitfishes that host A. sigani, Siganus lineatus and Siganus fuscescens. The twist was that rather than being the cercaria of a species of the genus Atractotrema, the adult match was an undescribed species of the genus Isorchis. We named this species Isorchis cannoni in honour of Dr. Lester Cannon and his work on trematodes of the Great Barrier Reef (and that he pretty much figured out the life-cycle for us already!).


Isorchis cannoni new species. A) Holotype, B) Ovarian complex




Species of Isorchis were previously known only from the milkfish Chanos chanos (family Chanidae) and the scat Selenotoca multifasciata (family Scatophagidae). This was all pretty rad as our study added a new host family to those known to be exploited by species of Isorchis and we revealed the first life-cycle known for the genus (actually the first life-cycle for a species of the Atractotrematidae). This life-cycle information may provide new insights into the evolutionary split between the Atractotrematidae and the Haploporidae, though we need to discover a few more life-cycles before we can truly delve.



References
Cannon, L. (1978) Marine cercariae from the gastropod Cerithium moniliferum Kiener at Heron Island, Great Barrier Reef. Proceedings of the Royal Society of Queensland, 89, 45-57.

 

Saturday, July 29, 2017

New publications - New species of Schikhobalotrema (Digenea: Haplosplanchnidae) and a note about Menemerus bivittatus (Araneae: Salticidae)

I'm happy to report I've got two new publications that have come out this month. The first was a long time coming, and includes a molecular phylogeny for the poorly studied digenean family Haplosplanchnidae. I also described a new species in the paper, Schikhobalotrema huffmani which I was very pleased to name after my friend, mentor and masters degree supervisor at Texas State University, Dr. David Huffman. No one deserves the honor more than him. Here is the citation and a link to the paper:

Huston, D.C., S.C. Cutmore, and T.H. Cribb. 2017. Molecular phylogeny of the Haplosplanchnata Olson, Cribb, Tkach, Bray and Littlewood, 2003, with a description of Schikhobalotrema huffmani n. sp. Acta Parasitologica, 62: 502–512. PDF on Researchgate

This family has barely been studied on the Great Barrier Reef, even though its looking like the group is a bit more diverse than we thought (more on that coming soon!). There are actually only two species of Haplosplanchnidae reported from the GBR, so this beast makes the third.



Schikhobalotrema huffmani from intestine of Tylosurus crocodilus, Lizard Island, Great Barrier Reef, Australia. A) Dorso-ventral B) Lateral C) Terminal Genitalia

I also included the first record for the species Haplosplanchnus pachysomus from Australia in the same paper. Here's a picture of the worm for your admiration:

Haplosplanchnus pachysomus from the intestine of Mugil cephalus, Moreton Bay, Australia

Parasites are pretty groovy but I'm also a bit of an amateur entomologist, and have published a few short papers and research notes on insects over the last couple years. I just got a short note published in the Australian Entomologist detailing some observations I made of a species of jumping spider, Menemerus bivittatus on the balcony of the old "Queenslander" style home I rented when I first moved to Brisbane. If you don't live in Brisbane, essential background information is that all our homes are infested with these tiny black ants called Technomyrmex sophiae. These critters aren't that much of a problem, and don't really get into your food or anything, but they will build nests in just about any small crevice. They seem to enjoy potted plants the best, but I have personally experienced small colonies living inside the machine bits of a blender, and behind the motherboard of my washing machine. The point here is, they are constantly moving house, and their little wagon trains are great targets for raiders.

Menemerus bivittatus is a pan-tropical species and is pretty common around here in Brisbane. We had them back in Texas as well, which is why they were so easily recognizable to me. Anyway, these spiders have some clever tricks. One such trick is train robbery, stealing the ants' precious larval cargo. The micro-world is a savage one. Check out the video I shot of this behaviour on YouTube.

Be sure to download the paper and give it a read. Heres the citation and a link:
Huston, D.C. Train Robbery: Menemerus bivittatus (Dufour, 1831) (Araneae: Salticidae) steals larvae of Technomyrmex sophiae Forel, 1902 (Hymenoptera: Formicidae) in transit. Australian Entomologist, 44: 85–88. PDF on ResearchGate.

 

Wednesday, May 10, 2017

Fieldwork in French Polynesia

Parasitology isn’t always glamorous, but I find it comes with perks. I just got back from a month of fieldwork in French Polynesia, and it was awesome.

Approaching Moorea, French Polynesia on the ferry from Tahiti    
Along with two other students from my lab, I was lucky enough to be invited over by Dr. Pierre Sasal to work on a project examining the parasites of three species of important aquaculture fish in French Polynesia: Chanos chanos, Siganus argenteus, and Platax orbicularis. While we were there we also had plenty of time to collect fish for our own research projects. For me that meant fish of the families Acanthuridae and Kyphosidae. I was also pleasantly surprised to get some interesting trematodes in the family Atractotrematidae from Chanos chanos and Siganus argenteus.

A beautiful Naso vlamingii I collected off Rangiroa in the Tuamotus. Species of Acanthuridae in the genus Naso have some very interesting haplosplanchnid trematodes that I am currently working on.

We spent our first two and our last week at the CRIOBE research facility in Moorea, a small island just off Tahiti.  Moorea is stunningly beautiful, and the water is warm and clear.  If you ever get to visit, be sure to try the local fruit juice. Baguettes are a given.

The bay we set out from each day on our way to the reef.

 Our third week was spent in Rangiroa, a large atoll in the Tuamotus. This place was far out.

Pretty sure I could live here

Although the trematode fauna of French Polynesia is relatively depauperate compared with the Great Barrier Reef, I was still able to make a pretty good collection.  I’ve got a lot of projects on my plate right now, but hopefully I’ll get around to working up my French Polynesian collection soon. French Polynesia was among the most beautiful places I’ve ever been, and being able to spend a month collecting there was a privilege I won’t soon forget.

 

Exploring the dark food web? Start with molluscs first.

Parasites with complex life cycles, such as the ubiquitous digenetic trematodes, exploit different hosts for different reasons (i.e. ase...