"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

August 19, 2016

Sclerodermus harmandi

This is the third post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2016. This particular post was written by Jarrod Mesken the more maternal side of a parasitoid wasp (see also the previous post about picky bat flies and monkey-infesting botflies).

When most people think of parasite behaviour, horrific tales of behavioural and physiological manipulation are what come to mind. This is not without cause; many parasites are definitely scary to think about. However, many pursuers of the parasitic lifestyle also display behaviour that would be thought of as normal, perhaps even charming in an anthropomorphic kind of way. An example of this is seen in the parasitoid wasp Sclerodermus harmandi, in the form of maternal care.

Photo of multiple female Sclerodermus harmandi engaging in brood care from Figure 1 of this paper

This stories begins when the female wasp finds a suitable host for her eggs. She injects the host with paralysing venom, and cleans an area of the body to lay eggs on. Once laid, she routinely inspects the eggs with her antennae and mouthparts. If an egg is found to have detached from the host, she would gently reattach it. Maternal behaviour continues when the eggs hatch, when the larvae must be fed. To do so, the mother wasp bites a hole in the host, which is still alive at this point and injected with paralysing venom periodically to prevent it from moving. The hole fills with haemolymph, the insect equivalent of blood, which is consumed by the larvae.

During this stage the mother S. harmandi also moves the larvae around to prevent them from overlapping each other as they grow. If a larva dies, the mother moves the body far from the other larvae to prevent their habitat becoming unsanitary. Even during the cocoon stage the mother continues to rub the offspring, despite them being encased. Eventually, the males of the clutch hatch out as adults. These few males (there is considerable female bias in the ratio of this species) chew holes in the female wasps’ cocoons to assist them in emerging, after which they mate with them. While it has negative affects in many taxa, this kind of inbreeding is less likely to have negative effects in hymenopteran insects, where haploid males act as a purge of deleterious alleles.

So why does S. harmandi provide such comprehensive maternal care? Because it increases the likelihood of offspring surviving. Experiments in which the wasp mothers were removed at varying stages of offspring development showed that not only were offspring that received maternal care more likely to survive to adulthood, but that this was proportional to how much maternal care they received. Experiments also showed that when a mother was taken away and replaced with another female who has previously laid eggs, the ‘stepmother’ will exhibit the same behaviour as the mother would, with the same rise in offspring survival.

Why the stepmother expend her own energy to raise another wasp’s offspring is just as interesting; it is because of the high levels of inbreeding in the population. Since most of the reproduction in this species is done through inbreeding, there isn’t much genetic variation going around. This means that there is a good chance of two wasps being related, so the stepmother may increase the chance of her genes being passed on by raising another wasp’s offspring. Female S. harmandi that haven’t laid eggs yet do not exhibit this behaviour, preferring to leave the offspring alone; this would indicate that the maternal behaviour is initiated by laying eggs.

So for a parasitoid wasp, it turns out that the females of S. harmandi make for very responsible parents or stepparents. That is, if you consider letting your children live on the body of something you paralysed, feeding off its blood until they grow up, and then mate with each other to be “responsible”.

Hu, Z., Zhao, X., Li, Y., Liu, X., & Zhang, Q. (2012). Maternal care in the parasitoid Sclerodermus harmandi (Hymenoptera: Bethylidae). PloS One 7: e51246.

This post was written by Jarrod Mesken

August 12, 2016

Alouattamyia baeri

This is the second post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2016. This particular post was written by Gabrielle Keaton and it is about a nasty botfly that lives in the neck of howler monkeys (you can read the previous post about picky bat flies that live on bats here).

Photo of botfly pores on howler monkey neck from Plate 1 of this paper
You know how itchy a mosquito bite can be - you scratch it then a lump forms. Imagine that lump forming but not going away. Instead, it grows and grows inside of you until finally a black grub plops out of a hole in your neck onto the ground. Well that’s what it’s like for the howler monkeys of Panama!

This nasty parasite in this case is the larvae of Alouattamyia baeri, a botfly that lives on free-ranging howler monkeys (Alouatta palliate). In a study conducted over seven years from 1987 to 1993, researcher Dr Katherine Milton investigated a variety of factors relating to this parasite's life cycle including its infection prevalence and intensity. She found that 60% of the howler monkeys on Barro Colorado Island (BCI) were infected by this botfly.

Alouattamyia baeri are large (18 to 20mm in length) black flies. The adult fly sounds and look like neotropical bees. When flies that were collected from the howler populations on BCI were reared in captivity, it was found that female flies produced an average 1400 eggs each, laid in discrete rows. These eggs required the appropriate stimuli (carbon dioxide and heat) to hatch into parasitic larvae that then invade their host through the nose and mouth where it migrates to the neck and opens a up larval pore. The larva reside in the howler’s neck for approximately 6 weeks, passing through 3 instars (developmental stages). After this, the larva drops out of the monkey's neck warble and burrows into the soil where it finishes the last developmental stage underground.  The study found that the entire life cycle takes approximately 13 weeks.

Dr Milton discovered that most of larval growth (86%) occurs during the 3rd instar when its food consumption increase by about 20%. This means the larva was trying to extract the most resources at the last possible moment of its stay, so if it ends up killing the host, it wouldn't matter to them because they are out of there.

Infestations were the highest during the wetter seasons and these periods also strongly correlated with peaks in the monkey’s mortality. Monkeys carrying the botfly larvae lack subcutaneous fat reserves. As if having a 2.4 centimetre long and 1.5 centimetre wide maggot in your neck wasn’t bad enough, even after the botfly has made its exit, the hole they made in their host remains open for several days. That’s pretty like much waving a neon ‘vacancy’ sign in front of the primary screw worm fly (Cochliomyia hominivorax) - an even nastier parasite that lays its eggs in open flesh wounds. When the screwfly larvae hatch, they feast on anything and everything surrounding that wound. Some monkey cadavers were even found with hands eaten down to the bone from these nasty little maggot and at least half of the C. hominivorax infestations found on howler monkeys were the result of prior A. baeri infections

Now, I’m sure you might have a bit of a panic next time you feel a little raised bump hanging around your neck, but remember - even if it is a botfly, at least you know it will be gone in 6 weeks' time.

Milton, K. (1996), Effects of bot fly (Alouattamyia baeri) parasitism on a free-ranging howler monkey (Alouatta palliata) population in Panama. Journal of Zoology 239: 39–63.

This post was written by Gabrielle Keaton

August 5, 2016

Trichobius sp.

Those who have been reading this blog for a while will know that August is student guest post month! All this month this blog will be featuring posts written by students from my Evolutionary Parasitology  (ZOOL329/529) class. One of the assessment I set for the students is for them to summarise a paper that they have read, and write it in the manner of a blog post. The best blog posts from the class are selected for re-posting (with their permission) here on the Parasite of the Day blog. I am pleased to be presenting these posts from the ZOOL329/529 class of 2016. To kick things off, here's a post by Melissa Chenery about some picky bat flies.
Photo of Trichobius johnsonae from Figure 2 of this paper

The public often view bats as repulsive, disease-carrying animals and are subsequently disliked. “Argh! They’re repulsive!” is just one of the many lines I have heard from people walking by while I observed a local colony. But do you know what is even more horrifying than a bat? A bat fly! These ectoparasites belong to two families of flies know as Streblidae and Nycteribiidae. But these hematophagous (blood-feeding) parasites don’t always fly like the name suggests - most species actually have no wings at all, and some look more like spiders than flies.

Disgusting, right? But not to worry, these external parasites have evolved to feed exclusively on bats. The bat flies are quite specific towards their hosts and tend to stay on a particular bat host. They are even picky about where they live on the host, whether on the bat’s fur or hiding within folded wing membranes. Occasionally they can be found in the fur and these individuals possessed comb-like structures (called ctenidia) for attaching to fur. It is assumed that long-legged species move quickly to avoid being scratched by the bat during grooming, whereas the short-legged species hide within the membrane folds to avoid getting licked. Bats use grooming as a behavioural defence against bat flies and other external parasites, and bats with a high number of flies groom more often than those with only a few. For the parasites, action can result in their removal and often their death.

In a study which took place in Belize, Central America, a team of researchers demonstrated just how host-specific the bat flies can be. They examined over thirty two species of bat flies, and in the twenty species for which they were able to collect more than five individuals, they found that eighteen of those species showed strong site preferences. The majority of the bat flies were constrained to a single host-species, and amazingly, bat flies with functional wings (which would allow them to be more mobile) weren't any more or less picky than those without. The study also found that only two species (Trichobius yunkeri and Trichobius dugesioides) weren’t too fussy in respect to host-site preference.

For bat flies that were the dominant species of their respective hosts, six out of those seven species were fur-specific, suggesting that in most cases, bat flies are highly host site-specific. They also discovered an interesting correlation between leg length and host-site preference. Bat flies with longer legs are able to push up over the surface of the fur, and are more likely to be found dwelling in fur. Conversely, short-legged individuals moved much more slowly and were mostly membrane-dwelling.

The team also conducted a study where three bats were restrained and three left unrestrained, with six bat flies placed on each. All unrestrained bats had only one bat fly remaining after five days, whereas all bat flies remained on the restrained bats. This suggests that the elimination of the flies is due to grooming behaviour. This may also be the cause of host-site specificity in bat flies, although further studies are needed Despite their nightmarish appearance, bat flies can still be very fussy eaters, and they have adaptations which allows them to specialise on particular bat species and host-sites.

Hofstede, H., Fenton, M., & Whitaker. J. (2004). Host and host-site specificity of bat flies (Diptera: Streblidae and Nycteribiidae) on neotropical bats (Chiroptera). Canadian Journal of Zoology 82: 616-626.

This post was written by Melissa Chenery

July 29, 2016

Gordionus kimberleyae

We have featured hairworms (Nematomorpha) quite a few times before on this blog, but for those who are new to them, they are parasitic body snatchers of insects and other terrestrial arthropods. The hairworm larvae are parasitic and must develop inside an arthropod host, but the adult worm is free-living and has to enter a water body in order to reproduce. To achieve that end, once they reach maturity, they make their host seek out a body of water and jump in, at which point the adult worm make their exit. This can look quite dramatic / horrifying to onlookers as the length of a fully grown hairworm can be several times longer than the host itself.

Specimens of Gordionus kimberlyae emerging from beetles, from Figure 2 of this paper
Hairworms are found all over the world, and the study we are featuring today shows that they can thrive even at the Arctic Circle, in the most northern parts of Canada. Despite the harsh conditions there, Arctic Canada is home to over 2000 species of terrestrial arthropods, including many species of beetles - some of which are host to parasitic hairworms.

In this study, a team of researchers sampled insects from twelve different locations in northern parts of Canada, and at five of those locations, they found seven species of beetles which are host to hairworms. All the hairworms they found belonged to a single species - a newly discovered one that has never been described before. They named it Gordionus kimberleyae, and these parasites happened to be most common in beetles on Banks Island in the Canadian Arctic Archipelago.

At Banks Island, 13.4% of the beetles that the research team collected were found with G. kimberleyae emerging from them. Most of the hairworms were found in beetles that were hanging around near water, and it's possible that those infected beetles weren't there by accident - as mentioned above, hairworms are known to modify their host's behaviour so that they would seek out water when the parasite is ready to exit their host. Most beetles were only infected with a single worm, which is bad enough considering how big they are and what they do to the host, but there were a few beetles that had two or even three inside them.

So how do these parasite manage to survive in the frigid cold of Arctic Canada? While adult hairworms don't do particular well in cold conditions, they are very short lived and die shortly after they reproduce anyway during the warmer months. However, the larvae have adaptations for surviving in freezing conditions.

In addition to the seven species found in this study, it's not clear how many other ground beetles that G. kimberleyae infects. The ground beetles which these hairworms infect are carnivorous insects, which means they probably acquire their hairworms from eating flying insects that have aquatic larval stage (such as mosquitoes) which can become host to these parasites' larvae. The beetles occupy an important part of the food web as the link between tiny invertebrates and larger insect-eating animals. But the hairworms may also be keeping their population in check.

Additionally, by causing their host to jump in the water, they are transferring where nutrients are flowing in the environment. While these beetles would usually be eaten by land-dwelling animals, by dunking their host in water, the hairworms may also be feeding a range of aquatic animals that depend on their hairworm's "donation" of dying insects into their realm. Despite their gruesome methods, parasites also play important roles in many ecosystems.

Ernst, C. M., Hanelt, B., & Buddle, C. M. (2016). Parasitism of ground beetles (Coleoptera: Carabidae) by a new species of hairworm (Nematomorpha: Gordiida) in Arctic Canada. Journal of Parasitology 102: 327-335

July 10, 2016

Cuscata campestris

One of the key characteristic of plants is their ability to produce food using sunlight via the process of photosynthesis. But there are many plants that do not photosynthesise - holoparasitic plants obtain all the nutrient they need from their host. One of the most well-known group of holoparasites are the dodders. There plants have no roots, their leaves have been reduced to tiny scales, and are composed entirely of elongated tendril-like vines. Because of their appearance and what they do to the host, the dodder has also acquired many common names including "Angel Hair", "Witch's Hair" and "Devil's Hair". When the dodder latches on to an appropriate host, it extends structure call haustoria which penetrate into the host plant's tissue to suck out its nutrients. This has led to the dodder also being called "vampire plants".
Dodder seedling in the process of coiling around its host (image from Fig. 1. of this paper)
There are 200 known Cuscuta species and of those, a small handful of them (10-15 species) are considered as serious agricultural weeds. These parasitic plants wrap their vines around their hosts and literally suck the life out of them. Infestation of this plant have been known to cause massive losses in alfalfa, tomatoes, carrots, and cranberry crops, and these "vampire plants" are very difficult to get rid off; since dodder vines often completely smother their hosts, it requires a lot of manual and mechanical labour to remove them. Additionally, dodders can also produce large numbers of resilient seeds that can linger in the soil for a long time, waiting for the next year to erupt in another outbreak.

For dodders, as with most other organism, the first moments of its life are the most critical - the newly germinated dodder seedling must secure a grip on a host plant within two to three weeks of germinating, otherwise the seedling would use up its energy reserves and expire. From the moment they germinate, these parasitic plants have various ways of finding their host. Dodder vines are able to "sniff out" host plants through the chemical they give off (essentially plant BO), but they can also use other senses to find their host. A newly germinated dodder seedling can also detect the specific wavelength of light which are reflected off the surface of plants, and use it to reach a host.

The scientists in this study investigated whether exposing dodder seedling to different spectrum of light can disrupt their ability to find their hosts. They conducted their experiments on the seedlings of two dodder species - Cuscuta campestris (which parasitises tomatoes) and Cuscata gronovii (which parasitises jewelweeds), and exposed them to three light source with different spectrums - the spectrum similar to unfiltered sunlight, mostly red light, and mostly far red light. Far red is a wavelength of light which is barely visible to our eyes, but it is the wavelength which is most reflected by the surface of plants. It is also the wavelength which dodders use to home in on their host.

From the experiment, the scientists found that almost all the dodder seedlings that were exposed to unfiltered light and mostly far red light were able to attach to a host after a week or two, in fact those bathed in far red light grew faster than the other groups. However, most of those that were bathed in red light lost their ways. Only 15% of the C. campestris and 27.2% of the C. gronovii seedling that were exposed to high levels of red light had managed to wrap themselves around a host.

So will it possible to control dodder infestation simply by bathing crops in red light? No, not quite since some dodder still managed to wrap themselves around a host plant and the red light treatment is only effective during the earliest stage of the dodder's life. But at least the findings of this experiments have shown that perhaps light manipulation can be combined with other control methods to control dodder infestation.  Additionally, we have gained an insight about how these parasitic plants sense and find their way through the world.

For this particular vampire, its weakness is not against sunlight, but rather, red light.

Johnson, B. I., De Moraes, C. M., & Mescher, M. C. (2016). Manipulation of light spectral quality disrupts host location and attachment by parasitic plants in the genus Cuscuta. Journal of Applied Ecology 53: 794-803.

P.S. I recently drew some dodder-inspired art, yes, it is more Parasite Monster Girls - meet Cassandra the Dodder...

June 23, 2016

Halipegus occidualis

The tongue-biter parasite is infamous for living inside the mouths of fish and replacing their tongue. But that parasitic crustacean is not the only parasite with a predilection for that part of host - the tongue is also the preferred site for some species of Halipegus, a genus of digenean trematode fluke that lives in frogs and toads. While Halipegus doesn't replace the tongue the way the tongue-biter does, but they are very particular about where they hangout. Specifically, the adult fluke attaches itself to the lingual vein under the frog's tongue.

Halipegus occidualis in the gray tree frog (left), Southern leopard frog (centre), American bullfrog (right)
Photos from Figure 1 of the paper 
While that may seem oddly specific on Halipegus' part, in fact many parasites are like that - not only are they particular about what host they infect, but they can also be very picky about which part of the host they live in. To a parasite, the host is a collection of very different habitats and only certain parts might meet the parasite's very specific needs. But not all hosts are equal, and a parasite that infect different species of host might also behave differently in each of them.

A pair of researchers from Oklahoma State University conducted a series of experiments to find out more about Halipegus' specific preferences. They collected seven different species of frogs and toads from various locations in Oklahoma, and infected them with a species of fluke call Halipegus occidualis to observed how the parasite behaved and developed in those different hosts. To control for natural variations and to ensure that the parasites they are using is the right species and not some other similar-looking cryptic species (see this for example), they used parasites from a colony of H. occidualis which they have been maintaining in their lab.

They exposed the frogs to larval H. occidualis by feeding them with seed shrimps which they have previously infected with H. occidualis. This procedure through which the frogs are exposed imitates the process of how frogs in the wild become infected with this parasite. After exposure, they inspected the frogs' mouths everyday for the parasite's presence. When H. occidualis is initially swallowed by a frog, it does so as a tiny larva encased in the body of an arthropod. The digestive action of the frog's stomach free the fluke from the arthropod host, and it then migrate to the frog's mouth over the course of a few weeks to develop into a sexually-mature adult. Or at least that's what happens in most frog species.

For six of the frog species in the experiments, H. occidualis showed up as expected under their tongue as mature, egg-laying flukes about 6-8 weeks after they have been fed with infected seed shrimps. The parasite was most successful at establishing in the American toads (93%) and had comparatively lowest success with the southern leopard frogs (67%), but aside from that, there were no major differences among those six species in terms of how H. occidualis performed. But things were a bit different in the American bullfrog. In that host, H. occidualis never show up under the tongue - instead, they simply stayed in the stomach and developed to full maturity there.

It seems that not only is H. occidualis very specific are where it settles, it will also adjust accordingly if the host is different, to the degree that it would do so even if it has already developed into a fully-fledged adult fluke. When the researchers conducted further experiments where they transplanted adult flukes from under the tongue of gray tree frogs to other species of frogs, the flukes were quick to adjust. When the flukes were transplanted from a gray tree frog to yet another gray tree frog or a green frog, the fluke will move to its usual spot under the host's tongue, even though it is now in a new host. But if those flukes were transplanted to an American bullfrog, the flukes would migrate to the bullfrog's stomach. Furthermore, when those parasites were then extracted from the bullfrog and transplanted back to the tree frog, they went back to living underneath the host's tongue.

So what so special about the bullfrog, or specifically its stomach? At this point, it is not entirely clear. Perhaps the bullfrog stomach has some kind of chemical that encourage the fluke to stay instead of migrating to the host's tongue. While a parasite might be very specific about where it exactly it lives in the host, it might not always behave the same way when it finds itself in different host species. For a parasite like H. occidualis, not all frogs are equal.

Stigge, H. A., & Bolek, M. G. (2016). Anuran Host Species Influences Site Fidelity of Halipegus occidualis. Journal of Parasitology 102: 47-53

June 10, 2016

Hexametra boddaertii

Nematodes (roundworms) are common parasites which are found in all kinds of animals. The study featured today is a report on a species of nematode reported for the first time in the false coral snake (Oxyrhopus guibei). The false coral snake is a non-venomous snake which mimics the highly venomous coral snakes. The snake in question had been living in captivity for a week at the National Institute of Tropical Medicine (INMeT) in Argentina before it suddenly died. It had appeared healthy until it just keeled over one day. When researchers dissected it, they found that it was full of parasitic roundworms that were identified as belonging to the species Hexametra boddaertii.
(A) The false coral snake a few days after arriving in captivity, (B) Hexametra boddaertii in the snake's body cavity,
(C) Parasitic roundworms in the bowel lumen of the snake, (D) roundworms extracted from the snake's intestine
Photos above from Fig 1 of the paper
The researchers found a total of 120 H. boddaertii in the snake; 68 of which were dwelling in the body cavity while a further 52 were living in the snake's digestive tract. This species of parasite has been recorded in other snakes before, but this is the first time it has been found in the false coral snake, and the first time that it has been reported from Argentina.

Hexametra boddaertii belongs to a group of parasitic roundworm call Ascarididae which also include roundworms that infect various domestic animals and humans. During the snake's stay in captivity, its carers had attempted to deworm it by giving it Fenbendazole - a de-worming drug which is commonly for treating parasitic infections in various domestic animals. They also tried to disinfect the enclosure, but neither seemed to have had any effects on the snake's parasite burden.

When the researchers performed a postmortem examination of the snake, they noticed that the worms found in the snake's body cavity were significantly smaller those found in the gut. On average, the worms dwelling in the body cavity were about 4 cm in length, while those from the gut were about twice as long. It is most likely that those smaller worms were juveniles - one of the key characteristics of ascaridid parasites (including Ascaris lumbricoides which infects humans) are their habit of travelling through the host's body cavity during their juvenile phase (think of it as their coming-of-age, "find yourself" trip) before entering the intestine to settle down and develop into an adult to start reproducing. And those 52 fully-mature worms in the gut had certainly been pretty busy as the snake's faeces were loaded with nematode eggs

But whether they were adults or juveniles, those parasites' presence certainly took their toll on the snake. Parts of the the snake's body cavity showed signs of calcification, its lungs were filled with excess fluid, and its gut lining were inflamed and congested. Given the number of worms the snake had and how well-developed most of them were, the snake most likely had acquired those parasites long before it was brought into captivity.

In addition to providing a new parasite record, this study also revealed a potential risk associated with handling snakes - larvae of other Hexametra nematodes from snake faeces have been reported to successfully infect the crab-eating macaque, so if given the opportunity, there is some potential for H. boddaetii to jump host into primates (including humans).

Sometimes when it comes handling snakes, it is not necessarily just the snake that you have to be careful of...

Peichoto, M. E. et al. (2016). First report of parasitism by Hexametra boddaertii (Nematoda: Ascaridae) in Oxyrhopus guibei (Serpentes: Colubridae). Veterinary Parasitology 224: 60-64.

May 26, 2016

Opechona olssoni

Jellyfish are one of the most common inhabitants of the sea and while they are soft and squishy, their venomous stinging cells (call cnidocytes) can act as a deterrent for many potential predators. But not all predator though - jellies are on the menu for a wide range of different marine animals including sea turtles and various species of fish - this is a fact which has been exploited by some species of parasitic flukes (digenean trematodes) as a mean of completing their life-cycles.
Clockwise from top left: Fluke larvae embedded in sea jelly tissue, close up of fluke larvae, Opechona olssoni from the gut of a butterfish, a juvenile butterfish collected from the Seto Inland Sea. Image modified from Figure 2, 9, 10 of the paper
Flukes have a rather complicated life-cycle which involves multiple different hosts. While the adult stage lives in vertebrate animals, they lay eggs that hatch into larvae which infect a "first intermediate host" (usually some kind of snail) where the parasite undergo asexual proliferation, producing a different type of clonal larval stages that infect a "second intermediate host" which serves as a vehicle to reach the vertebrate host. This is usually accomplished through the vertebrate host eating the second intermediate host. For some species of flukes, such as Opechona olssoni, the second intermediate hosts are sea jellies, and it is not alone - some of its fellow travellers include Leptotrema clavatum and Cephalolepidapedon saba - all flukes from the Lepocreadiidae family which is commonly known to use gelatinous animals as their second host.

In this study, a team of researchers in Japan set out to examine the seasonal pattern in the abundance of parasitic fluke larvae found in some of the jellyfish inhabiting the Seto Inland Sea. Over the course of two and a half years from March 2010 to September 2012, they collected three different species of jellyfish: the moon jelly (Aurelia aurita), the Japanese sea nettle (Chrysaora pacifica). and the ghost jellyfish (Cyanae nozakii).

They noticed that while the fluke larvae were consistent present in the jellyfishes for most the year, their abundance varied over different seasons. Sea jellies were most heavily infected during the middle of the year when it is the warmest. Since the free-swimming clonal larvae of digenean fluke use temperature as their trigger to leave the first intermediate host, when things start heating up, they come streaming out of their host in large numbers.

Out of the three different species jellyfish species they sampled, the ghost jellyfish was the host with the most. While the moon jelly and the sea nettle on average harboured about 28 and 8 fluke cysts respectively, the ghost jellyfish had on average almost 150 fluke larvae, with some individuals carrying over 400 cysts in their tissue. But why are the ghost jellyfish so much more heavily infected than the other jellies? It is only slightly bigger than those other species, so size alone cannot be the answer.

Well, the ghost jellyfish is also known to prey on other gelatinous animals, and by doing so it could have been accumulating an impressive collection of fluke larvae second-hand (so to speak). Due to its jelly-eating ways, the ghost jellyfish earns itself the dubious distinction of serving as a hub for all these flukes to come together as they wait for a final host to come along and gobble them up.

But if the sea jellies are the second intermediate host for O. olssoni and friends, then what are the final hosts where the parasites mature into their adult form? Flukes from the Lepocreadiidae usually use fish as their final host, so the researchers also collected some fish species which are known to either associated with and/or have jellyfish on their menus, since they are the most likely final host for those parasites. They examined their gut content for bits of half-digested jellyfish and the adult form of the jelly-infecting fluke species.

One of the fish which they found to harbour maturing and/or adult flukes is the Japanese butterfish. Juvenile butterfish are known to hangout around the tentacles of jellies, using them for food and shelter, taking a few nibbles here and there whenever they get peckish.  Alongside the butterfish, another species that hosts those flukes is a filefish known as the black scraper. It eats a variety of different marine invertebrates, but is known to partake in some jellies now and then.

For these small fish, hanging out around jellyfishes is a pretty good deal - the curtain of tentacles act as a shelter from their predators, and the shelter itself is edible too. But because the jellyfish's tissue is also laced with fluke larvae, it means that every mouthful of jellies those fish swallow also goes down with a bunch of parasite larvae. As with everything in life, there is always a catch

Kondo, Y. et al. (2016). Seasonal changes in infection with trematode species utilizing jellyfish as hosts: evidence of transmission to definitive host fish via medusivory. Parasite, 23: 16

P.S. Some of you might know through my activities on Twitter (@The_Episiarch) that when I'm not writing these blog posts about new scientific papers about various parasites, I also do illustrations. Some of my drawings are about and/or inspired by parasites, however some may find my more recent parasite-inspired pieces to be slightly unusual - I am of course talking about Parasite Monster Girls...

May 12, 2016

Cystodiscus axonis

Myxozoans are a group of very unusual parasites. Despite their simplified structure, latest research has shown that their closest living relatives are actually jellyfish (which means they are technically animals). They are found in a variety of tissues and organs in their hosts which are usually fish, and in some cases, amphibians. Some causes diseases such as the salmon whirling disease, and in the case of certain fish-infected myxozoans, after the host dies, the parasite causes the flesh to melt - much to the frustration of fishermen. While the majority of known myxozoans infect fish, in the last decade, there has been increasing interest in studying myxozoans that infect amphibians, and the parasite featured today is one such species.
Photo of Cystodiscus axonis spore from this paper

Cystodiscus axonis is a myxozoan species which lives in either the brain or the gall bladder of their frog hosts. This parasite and its close relative C. australis is found in a range of native Australian frogs. This parasite was previously classified in another genus called Myxidium and its discovery (and reclassification) featured a number of twist and turns.

The parasite was first recorded in cane toads which have been introduced to Australia, so it was originally thought to be a parasite that the cane toads had brought with them into Australia and had since taken to infecting Australia's native amphibians. However, examinations of older frog specimens from museum collections, including those that were collected before the introduction of cane toads to Australia, revealed that the parasite had been in native Australian frog all along - the cane toad simply picked it up when they arrived and they turned out to be a really hospitable home for this parasite.

Given that C. axonis is not too discriminating when it comes to whether it infects native Australian frogs or introduced cane toads, there is potential for this parasite to infect other amphibians as well. And that's what the scientists behind today's featured study decided to find out. This time, they once again look to museum specimens, in this case from the Natural History Museum in London, and specifically they examined preserved specimens of caecilians for myxozoan parasites

Caecilians are very strange looking amphibians - they are legless, look kind of like giant earthworms, and they are very different to either toads and frogs. For this study, the scientists examined 148 caecilian specimens spanning across twelve species which are found in a variety kind of habitats, ranging from terrestrial, burrowing forms to aquatic species. Out of those, they found seven specimens which had myxozoan spores floating in their gall bladder. All the infected caecilians belong to one of two species - Typhlonectes natans and Typhlonectes compessicauda - and both of them are aquatic caecilians.

Based on the shape of those spores and sequences of their DNA, the parasite they found was almost identical to C. axonis from Australian frogs. So somehow, C. axonis has managed to successfully make a jump to caecilians too - but how? The native frogs of Australian and caecilians are separated not just by a vast ocean, but also 300 million years of divergent evolution - so how did these legless amphibian parasites end up with a parasite which is originally found in Australian frogs? A vital clue might be the fact that the infected specimens were originally captive animals.

Myxozoans use different host in their lifecycle - they usually alternate between a vertebrate and invertebrate host, so the infected caecilians might have become infected when they were fed invertebrates, such as tubifex worms, which were parasitised by C. axonis. Alternatively, they might have been housed or shared a water supply with other captive amphibians that were infected.

Given its ability to jump to a dissimilar host like caecilians, this explains why they were so receptive to cane toads when they were brought to Australian. Compared with the evolutionary gulf that separate frogs from caecilians, the native frogs of Australia and the introduced cane toads are practically kissing cousins. Given the presence of an Australian frog parasite in South American caecilians, just how widespread have C. axonis and similar parasite have become?

The lethal amphibian chytrid fungus Batrachochytrium is an amphibian pathogen which has now been spread all over the world due to the global trade in amphibians. So what other parasites might be lurking in the loads of frogs, salamanders, and caecilians which are currently being shipped all over the globe?

Hartigan, A., Wilkinson, M., Gower, D. J., Streicher, J. W., Holzer, A. S., & Okamura, B. (2016). Myxozoan infections of caecilians demonstrate broad host specificity and indicate a link with human activity. International Journal for Parasitology 46: 375-381.

April 25, 2016

Trophomera marionensis

This planet is full of parasites, and no matter what you are or where you live, there seems to be no escape from getting parasitised. A few years ago, I wrote a post about some microsporidian parasites which live in deep sea nematodes (roundworms) - well this time it is a deep sea nematode which is the parasite. Trophomera marionensis is a nematode which is found in one of the deepest part of the ocean, in the inky depths of the Kermadec Trench about 7000 to 10000 metres below sea level. This is a part of the ocean known as the Hadal Zone - a realm of perpetual darkness and immense water pressure, named after the underworld of Greek mythology.

Sample of the deep sea amphipods (top left), parasitised H. dubia (bottom right), an immature female T. marionensis (right)
Image from Fig. 1 and Fig. 4 of the paper
Trophomera marionensis belongs to a family of roundworms call Benthimermithidae which are mostly found in the deep sea. They share a similar lifecycle to the Mermithidae and Marimermithidae families which are found in the sunlit realm - some of which have previously been featured on this blog here, here, and here. Much like those families of nematodes, the benthimermithids are also body-snatchers that infects their host, take over the insides, and make a xenomorph-style exit at the end of their stay. But whereas those shallow water roundworms infect mostly insects and crustaceans, these deep sea nematodes are found in a more diverse range of hosts.

While T. marionensis infects the deep sea amphipod Hirondellea dubia which makes it comparable to some of its shallow water marine mermithid cousins, the hosts of the other 40 or so known species of Trophomera covers a wide variety of deep sea invertebrate animals. Given how sparsely distributed potential hosts are in the deep sea, you tend to take what you can get. The ecology of the hadal zone had placed enormous evolutionary selection pressure on the benthimermithids to diversify and infect invertebrates other than just arthropods. In addition to infecting deep sea crustaceans, species from that genus have been recorded from priapuplid worms (also known as the penis worm), mussels, and even other nematodes.

Much like other deep sea creatures, the population of T. marionensis is very sparsely distributed. Out of the several thousand amphipods that the researchers examined, they only came across 32 infected ones, containing a total of 40 worms. Most amphipods were infected with a single worm, though there was one rather unfortunate individual that was host to four worms. Furthermore, all the worms they found were female worms - so at this point we don't know how the male worms look like!

The most likely way that those deep sea amphipods become infected by T. marionensis is through accidentally ingesting the larval parasite during early stages of their development, while feeding on scraps of "marine snow" which had settled on sea floor. Currently, it is unclear what effects T. marionensis has on its crustacean host, but given the size of this nematode in comparison with the amphipod, they must have at least some effects on their growth and reproduction.

Amphipods are common in deep sea habitats, and benthimermithid nematodes have also been recorded in deep sea environments from all over the world. So there is no doubt there are many more parasite-host combinations lurking in the dark abyss of deep sea habitats which are yet to be discovered.

Leduc, D., & Wilson, J. (2016). Benthimermithid nematode parasites of the amphipod Hirondellea dubia in the Kermadec Trench. Parasitology Research 115: 1675-1682