Acanthocephalus galaxii

The brown trout (Salmo trutta), a popular angling species, was introduced to the waters of New Zealand in 1867 and has become very well established in the local freshwater system. The trout have made New Zealand their own all-you-can-eat buffet, feeding on many of New Zealand's native freshwater fishes. But other native fauna have also been getting intimate with the trout in a different way. It turns out that during its time in Aotearoa, the brown trout has also picking up a new parasite - Acanthocephalus galaxii, which normally infects a little native fish call the roundhead galaxias (Galaxias anomalus).

Furthermore, the parasitic worm has actually become more abundant in the introduced trout than in the native galaxids - presumably because when compared with the tiny native fish, the much larger trout gobbles up more amphipods (the crustacean which carries the larval stage of A. galaxii). But this isn't necessarily good news for the parasite. Once they get into the trout, because of physiological incompatibility with the introduced host, the parasites are unable to reach maturity. So the trout actually acts as a kind of dead-end sink for the worm, which in turn reduces parasite burden on the native fishes.

So even while the trout might be chomping up native galaxids by the mouthful, they also are inadvertently reducing their parasite burden - though I doubt that would give much comfort to the little galaxids fleeing from a hungry trout!

References:
Paterson, R.A., Townsend, C.R., Poulin, R. and Tompkins, D.M. (2011) Introduced brown trout alter native acanthocephalan infections in native fish. Journal of Animal Ecology 88: 990-998.

Isospora lesouefi

Isospora lesouefi is a coccidian parasite which infects the Regent Honeyeater (Xanthomyza phrygia), an endangered species of bird found in Australia. This parasite was found and described during a parasitological survey conducted on a group of honeyeaters at Taronga Zoo as a part of their captive breeding programme.

Before the birds can be released into the wild, their health needs to be assessed and a part of that procedure involves determining their parasite load. For animals that you want to keep alive, this usually involves counting the number of parasite eggs or spores found in their faeces. But here's the tricky bit - it turns out that I. lesouefi keeps to a daily timetable. The researchers in this study found that bird faeces collected in the afternoon contained about 200 times more oocysts (the parasite's infective stage) than those collected in the morning. Other species of Isospora also keep similar shedding schedules, and it is likely to be an adaptive trait which minimise the oocysts' exposure to desiccation and ultraviolet radiation.

This study illustrates the importance of taking multiple samples, as well as understanding the life history of the parasites when you want to obtain an accurate picture of parasite burden, and its actual impact on the health of an animal.

Reference:
Morin-Adeline, V., Vogelnest, L. Dhand, N.K., Shiels, M., Angus, W. and Šlapeta, J. (2011) Afternoon shedding of a new species of Isospora (Apicomplexa) in the endangered Regent Honeyeater (Xanthomyza phrygia). Parasitology 138: 713-724

Myxidium sp.

When species of plants and animals are introduced to a new environment, this can often lead to some unexpected consequences. The parasite for today is Myxidium sp. - a myxosporean that lives in the liver and brain of native frogs in Australia. But in addition to the native amphibians, this parasite is also found in the invasive cane toad. The cane toad was introduced into Australia to control cane beetles, but has since become one of the most famous posterchildren of invasive species. While Myxidium was originally thought to have been a "present" brought to Australia by the cane toad, recent research indicates that it might actually be native to Australia.

The infamous cane toad does play a role in the story of Myxidium, but in a different manner to what was originally suspected. A collaborative group of researchers from Australia and the Czech Republic found that instead of bringing Myxidium to Australia, the toad has become embroiled in an ecological phenomenon known as "spillback". This is when a native parasite adopts a newly introduced host, this new species turns out to be a better host for the parasite than the native species it was originally infecting, and the parasite propogates more successfully in the new host species.

This can have dire consequences for the original host because the introduced species acts as an ampilifier for the parasite. As a result, the original host become exposed to more of the parasite than ever before. Because many parasites often have dose-dependent effects, this can mean a parasite, which would otherwise be tolerated, can become debilitating or even deadly to its original host.

Reference (and photo):
Hartigan A, Fiala I, Dyková I, Jirků M, Okimoto B, et al. (2011) A Suspected Parasite Spill-Back of Two Novel Myxidium spp. (Myxosporea) Causing Disease in Australian Endemic Frogs Found in the Invasive Cane Toad. PLoS ONE 6(4): e18871. doi:10.1371/journal.pone.0018871

Trypanosoma irwini

Today's parasite is about as Aussie as they come - Trypanosoma irwini - a blood parasite named in honour of the late Steve "Crocodile Hunter" Irwin. What's more, this parasite infects an iconic Australian host, none other than the Koala (Phascolarctos cinereus). While the vector host for T. irwini is currently unknown, it is likely that this parasite features a life-cycle broadly similar to other trypanosomes we have featured on this blog - that is alternating sexual and asexual stages in a vector host and a vertebrate host. Trypanosoma irwini is by no mean the only unique Trypanosoma found in Australian. Scientists have been describing many novel species of Trypanosoma from the marsupials of Australia, and no doubt there are many, many more waiting to be discovered.

In addition to T. irwini, the Koala is also infected by two other species of Trypanosoma. While on its own, T. irwini seems to be pretty benign, if it gets mixed up with the other Trypanosoma species or other infections such as chlamydia or the retrovirus which causes koala AIDS syndrome, it can lead to disease in its host. Like many other parasites, the pathogenecity of T. irwini is not so straightforward, and may only manifest itself under certain conditions.

Photo from McInnes et al. (2009)

References:

McInnes, L.M., Gillett, A., Ryan, U.M., Austen, J., Campbell, R.S.F., Hanger, J. and Reid, S.A. (2009) Tryapnosoma irwini n. sp. (Sarcomastigophora: Trypanosomatidae) from the koala (Phascolarctos cinereus). Parasitology 136: 875-885.

McInnes, L.M., Gillett, A.,Hanger, J., Reid, S.A. and Ryan, U.M. (2011) The potential impact of native Australian trypanosome infections on the health of koala (Phascolarctos cinereus). Parasitology 138: 873-883

Gnathia auresmaculosa

The harmfulness of parasites to their host is not always so straightforward, there are often many factors which contribute to the pathology of an infection. The parasite we are looking at today is Gnathia auresmaculosa - a type of blood-sucking crustacean with an interesting life cycle (which you can read about in this post from last year). These little gnathiids are like ticks of the sea, clinging onto passing fish and gorging themselves on blood before dropping off to continue developing. For adult fish, a few gnathiid here and there is probably not a big deal, but for growing juveniles, that is another matter.

Settlement is a critical transitional stage for coral reef fishes, and that is also when they are most vulnerable to parasites like G. auresmaculosa. A recent study by the lab group of Dr. Alexandra Grutter revealed just how costly these ticks of the sea can be to juvenile fishes. Dr. Grutter and her colleagues found that juvenile damselfish which have been fed on by just one of those little blood-suckers exhibit significantly decreased swimming ability, far higher oxygen consumption rate, and are about half as likely to survive than uninfected fishes.

So if you happen to find yourself on a beautiful tropical reef, take a moment to think about all the little baby fishes which are swimming for their lives through the gauntlet of gnathiids - they never mentioned that in Finding Nemo!

Reference:
Grutter, A.S., Crean, A.J., Curtis, L.M., Kuris, A.M., Warner, R.R. and McCormick, M.I. (2011) Indirect effects of an ectoparasite reduce successful establishment of a damselfish at settlement. Functional Ecology 25: 586-594

Eustrongylides ignotus

Eustrongylides ignotus is an extremely pathogenic nematode which lives in the wall of the stomach (proventriculus) of herons and egrets and has caused die-offs in nesting colonies of some birds. Its bright color has earned it the nickname of “the big red worm.” The life cycle involves oligochaetes as the first intermediate host and various fish as the infective intermediate host. If the small fish are ingested by larger fish, reptiles, or amphibians, these can act as transport hosts. The color in this larval worm in a mosquitofish has been bleached out by the preservative. If straightened out, it would be longer than the fish.

Contributed by Mike Kinsella.

Clistobothrium carcharodoni

The parasite for today is found in a celebrity of sorts, the star of the film Jaws and its sequels - the famous Great White Shark. Unlike its host - which is well-known for being big in every sense - Clistobothrium carcharodoni is a tiny little worm measuring no more than a few millimeters in length. However, what they lack in size, they make up for in numbers, as over 2000 of them can be found in a single shark.

Tapeworms in general have complex life-cycles with many different hosts, and C. carcharodoni is no different. The life cycle of tapeworms which live in marine animals such as the great white shark are difficult to unravel. That is because the larvae lack many of the diagnostic characteristics which are used to identify the adult worms, so it is next to impossible to match the identity of the larvae with adults based on their morphologies. But with the advent of molecular techniques such mystery are becoming more commonly solved.

One of my former colleagues from Otago University - Haseeb Randhawa - was able to use key genetic markers to confirm that adult C. carcharodoni found in the gut of great white sharks were identical to tapeworm larvae which have previously been found in dolphins. These larval tapeworms congregate in the tail, back, belly and groin region of the dolphins - all parts preferred by the great white sharks as the finest cuts of meat from Flipper. His study confirmed the role of dolphins in completing the life-cycle of C. carcharodoni.

So while Flipper and Jaws are famous superstars which grab all the public attention, to a tapeworm like C. carcharodoni, all those aquatic celebrities simply serve as way stations in the cycle of life.

Reference:
Randhawa, H. (2011) Insights using a molecular approach into the life cycle of a tapeworm infecting great white sharks. Journal of Parasitology 97: 275-280.

Chondracanthus parvus

Chondracanthus parvus is a parasitic copepod that parasitises the smooth-cheek sculpin, Eurymen hyrinus, by attaching itself to the inner side of the fish's operculum (the flap covering the fish's gills). Chondracanthus parvus belongs to a family of parasitic copepods known as the chondracanthids, which contains 160 species, all of which are parasites of marine fishes. Phylogenetic studies of the chondracanthids indicate that these copepod have consistently co-evolved with their hosts, and their phylogeny closely reflects the evolutionary history of the fish that they infect. Such parasites are like heirlooms of the evolutionary past and phylogenetic studies conducted on these living markers can in turn shed light on the evolutionary history of their hosts.

Picture from Ho et al. (2006).

References:

Paterson, A.M. and Poulin, R. (1999) Have chondracanthid copepods co-speciated with their teleost hosts? Systematic Parasitology 44:79-85.

Ho, J-s., Kim, I-H., and Nagasawa, K. (2006) Copepod parasites of the fatheads (Pisces, Psychrolutidae) and their implication on the phylogenetic relationships of Psychrolutid genera. Zoological Science 22:411-425.

Herpyllobius vanhoeffeni

Regular readers of this blog will no doubt be familiar with the wonderfully weird and twisted morphology of parasitic copepods. However, this is probably the weirdest we have featured yet. Herpyllobius vanhoeffeni is a spooky-looking parasitic copepod which has all the trappings you might associate with an Lovercraftian horror tale. They are found in the Antarctic Penninsula, in waters 666-673m deep, and they parasitise a polychaete worm, Eulagisca corrientis.

The top picture shows a pair of females attached to the ventral surface of their host; note that the lower individual has a pair of lobe-shaped egg sacs extending from its side like wings. The bottom picture shows a specimen that has been dissected from the host, showing the rest of the copepod, which is usually embedded in the host. Overall, the whole parasite looks not unlike a bulbous skull resting atop a twisted stalk of a body.

Reference:
López-González, P.J. and Bresciani, J. (2001) New Antarctic records of Herpyllobius Steenstrup and Lütken, 1861 (parasitic Copepoda) from the EASIZ-III cruise, with description of two new species. Scientia Marina 65:357-366

Columbicola extinctus

Speaking of co-extinctions, here's a contribution that I just got from Anya Gonchar. Columbicola extinctus is a louse that was specific to the Passenger Pigeon, the bird that forever disappeared in the early 20th century. In addition to many advantages of the narrow specialization, C. extinctus has experienced the most drastic of its drawbacks: it has followed its only host into extinction. This could have been one of the impressive examples for a discussion regarding specialist vs. generalist strategies in parasites, if the story hadn't suddenly taken a happy turn. C. extinctus was rediscovered from the Band-tailed Pigeon, while its fellow pseudo-extinct louse C. defectus was suggested to belong to a different species Campanulotes flavus that is still safe and sound. Still, parasite coextinction is documented in numerous other cases where we may not count on such good luck. Fortunately, there is now a large body of literature featuring related topics so that the problem is not neglected. The origin of this blog goes back to celebrating the year 2010 as an International Biodiversity Year. As the previous entries have shown, parasite diversity is enormous indeed. Yet, some parasite species’ existence is challenged. Further reading: Koh L. P. et al. 2004. Species coextinctions and the biodiversity crisis. Science 305, 1632. Dunn R. R. et al. 2009. The sixth mass coextinction: are most endangered species parasites and mutualists? Proc. R. Soc. B, 276, 3037-3045. Clayton D.H., Johnson K.P. 2003. Linking coevolutionary history to ecological process: doves and lice. Evolution, 57(10), 2335–2341. Johnson K.P. et al. 2003. When do parasites fail to speciate in response to host speciation? Syst. Biol. 52(1), 37–47. Johnson K.P. et al. 2009. Competition promotes the evolution of host eneralists in obligate parasites. Proc. R. Soc. B, 276, 3921–3926. Image is of Campanulotes flavus, from the paper: Price et al. 2000. Pigeon lice down under: taxonomy of Australian Campanulotes (Phthiraptera:Philopteridae), with a description of C. durdeni n. sp. Journal of Parasitology 86:948-950.