Sarcocystis cernae

This is the fifth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2014. This particular post was written by Reece Dalais that he had titled "A fuzzy shuttle bus to a feathery airport" about what the parasite Sarcocystis does to its vole host (you can read the previous post about a midge that sucks blood from the belly of mosquitoes here).

Photo from here

Many protozoan parasites make use of one or more hosts before finally infecting the host species with suitable real estate for sexual reproduction (e.g. Sarcocystis dispersa and S. putorii). These ‘intermediate’ hosts act as temporary living quarters, in which the parasite accumulates resources, multiplies and then prepares for the trip to the next neighbourhood. In the Netherlands, the protozoan parasite Sarcocystis cernae, uses its intermediate host, the common vole (Microtus arvalis), to multiply itself and then as a vehicle to its honeymoon suite – the small intestine of the common kestrel (Falco tinnunculus). In the lining of the kestrel’s intestine, S. cernae lays its sporocysts, (which are equivalent to eggs) which leave the intestine with the stool of the bird.

Voles forage daily at regular intervals before scurrying back underground. During this time, they can accidentally consume kestrel faeces as they eat vegetation. Once inside the common vole, S. cernae develop in the rodent’s liver before entering its bloodstream and then declaring war on its muscles. In the vole’s musculature the parasite sits tight, and multiplies (asexually) to form large cysts – known as statocysts – which contain numerous bodies capable of sexual reproduction – or cystozoites. These cystozoites break free to reproduce (sexually) once the vole is torn apart and ingested by an adult kestrel or its young – which become the future protozoan distributors. In the mid to late 1980s, it was been discovered by a pair of scientists (Hoogenboom and Dijkstra) that infection with S. cernae makes the vole twice as likely to be taken in aerial attacks. The reason for this is still under question, and has oddly been ignored by researchers since 1987. Could it be due to some form of host manipulation whereby S. cernae forces a change in the behaviour in the vole? Or is it merely a helpful side effect caused by the protozoan running amuck inside the vole’s muscles?

Photo by Małgorzata Miłaszewska

The researchers collected vole samples by snap trapping and from nest boxes during the breeding season. Voles brought to the kestrel nestboxes for their young were taken and replaced them with lab mice of a similar weight – so feeding could continue as usual. Once these voles were dissected, the results revealed that 92% of infected voles had cysts present in the locomotory muscles (the biceps, triceps and quadriceps) – the muscles responsible for movement. Hence it is likely that infected voles were slower to escape the kestrels than their Sarcocystis-free pals. However, it was also proposed that once a vole becomes infected with S. cernae they may be forced to find food at dangerous times. Without infection, voles forage at the same time as other voles and, as a group, are more aware of predators. So if these inbuilt rhythms were to be interrupted by a parasite, the vole would become an easier target. This would be an example of host manipulation, as S. cernae, would be forcing the vole to change its foraging behaviour.

Although the effect of S. cernae on the common vole is not completely understood, it is without doubt that the cunning protozoan helps to drive its furry rodent host towards a feathery final destination.

Reference:
Hoogenboom, I., Dijkstra, C. (1987) Sarcocystis cernae: A parasite increasing the risk of predation of its intermediate host, Microtis arvalis. Oecologia 74: 86-92

This post was written by Reece Dalais

Gordionus chinensis

Hairworms are known for their ability to make their host go for an impromptu (and terminal) swim in a stream or a pond, but by doing that they are not just sending ripples through the water, but also into the surrounding ecosystem. The paper we are looking at today features a species of hairworm from Japan call Gordionus chinensis - this parasite infects three different species of forest-dwelling camel crickets from the genus Diestrammena.

Photo by Danue Sachiko from here

The scientists who conducted the study that this paper is based on wanted to find out what happens to the the cricket population and their hairworm parasites after their home forest has been cut down. They conducted an observational field study at an experimental forest in the upper parts of the Totsu River at Nara Prefecture, Japan. The forest was originally clear-cut in 1912 and 1916 and since then, parts of it have been replanted and cut down at different point in time over the last century. Each study site corresponds with a different replanted forests of Japanese cypress ranging from 3 to 48 years old.

These scientists found that the camel crickets began returning a few years after a forest has been replanted, their abundance steadily increasing and eventually reaching a peak after the forest has been standing for at least 30 years. But their hairworm parasites did not return with similar gusto. In fact, they estimated that only second-growth forests that are more than 50 years old have hairworm populations that are as abundance as those found at undisturbed sites.

One possible reason for the hairworms' slow recovery is their complex life cycle which requires infection of more than one host. The replanted forest might be lacking some of the other host G. chinensis needs to complete its life cycle. Because parasites has such a negative public image, a forest which is free of parasites (or at least a specific parasite) might sound good to most people. But these hairworms actually play a very vital role in the ecosystem.

By causing their cricket host to jump into a stream, they actually serve as a kind of fast food delivery service for the fish living in those streams. A cricket infected with a hair worm is 20 times more likely to stumble into a stream and become fish food than an uninfected cricket - so fish which would not usually get to feed on such large land-loving insects on a regular basis can now do so thanks to the hairworm, and it has calculated that this straight-to-your-stream food delivery service accounts for 60% of the trout population's energy intake in some watersheds.

For hairworms, new forests just do not have the same creature comforts of old forests. And if you are a keen angler or simply appreciate a fish-rich stream - you have a parasite to thank for all the fishes.

Reference:
Sato, T., Watanabe, K., Fukushima, K., & Tokuchi, N. (2014). Parasites and forest chronosequence: Long-term recovery of nematomorph parasites after clear-cut logging. Forest Ecology and Management, 314: 166-171.

Sphaerularia vespae

Hornets can put fear into the minds of many people, but today meet the parasite that the hornets fear (if they are capable of fear). Sphaerularia vespae is a parasitic nematode that infects the Japanese yellow hornet (Vespa simillima) and as far as infection goes, this one is quite a doozy. It specifically invade and resides in the gaster (abdomen) of female hornets where it grows and develop. The nematode ends up sterilising the host (much like other parasitic castrators we have featured on this blog), turning her into a cozy nursery for baby worms. But a new study has shown that they are capable of doing more than just castrate the hornet.

Photo of a queen hornet (from Fig. 2 of the paper)

In a previous study, a group of scientists noticed that the majority of overwintered hornet queens caught in bait traps were infected with S. vespae, so there is something about these nematode-infected hornets which seems to make them more likely to end up in those traps. During autumn/fall, queen hornets fortunate enough not to be infected with S. vespae would visit and poke around various nooks and crannies (usually decayed logs) in the forest to find a spot to hibernate. When the hornet find a place she likes, she will start excavating a hibernacula ( a place to hibernate) and line it with plant fibres that serve as nesting material. But queens that are parasitised and sterilised by S. vespae start visiting decaying logs much earlier during early to mid-summer.

A team of scientists in Japan decided to find out just what those infected queens are up to. For three months between May and August, they made regular weekly visits to a predesignated sites in a forest at the foot of Mount Moiwa and set up a video cameras to observe the decayed logs in the morning and afternoon.

Photo of a hornet releasing
some S. vespae juveniles
(from Fig. 2 of the paper)

They saw that unlike other hornets, the nematode-infected queens never dig nor gather nesting material. They simply crawl inside a decayed log, hang out for a while, then fly off. That is because they have become sterilised couriers that visited potential hibernation sites only to drop off a special package in the form of S. vespae juveniles. A quarter of the infect queens they saw landing on decayed logs offloaded some nematodes (there were some hornets that moved out of sight so the scientist couldn't see what they were up to). But in addition to those observations, the scientists also captured some hornet queens and brought them back to the laboratory for further examination. They kept them in vials and noticed that over two-third of the infected hornets ended up releasing juvenile worms.

When they dissected hornets to see how many of them were infected and to check the developmental stage of their parasites, they found a seasonal pattern to the infections. Queens caught during May and June were mostly infected with fully-mature female worms and their eggs, while queens caught between July and throughout August were filled with juvenile worms that were ready to disembark and infect a new host - which just so happen to be the period when parasitised queens start making regular visits to potential hibernation sites.

So that is S. vespae's game - use the hornet as a mobile incubator/nursery, fly her around during summer to scope out the best pieces of real estate around the forest, then drop off a bundle of worms that can lie in wait like a booby-trap for an uninfected hornet queen to come along and settle in for winter. To complete its life cycle, S. vespae simply take advantage of a preexisting behaviour (seeking out hibernation sites) from the host's repertoire, and "switch it on" at a different time of year to fit the developmental schedule of the parasite's own offspring. Parasite manipulation isn't necessarily about teaching an old host new tricks, but to get the host to perform the tricks that it already knows in a brand new context.

Reference:
Sayama, K., Kosaka, H., & Makino, S. (2013) Release of juvenile nematodes at hibernation sites by overwintered queens of the hornet Vespa simillima. Insectes Sociaux 60: 383-388.

Plasmodium relictum (revisited)

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 2013. This particular post was written by David Rex Mitchell on a paper published just this year on how an avian malaria parasite might make its bird host more attractive to mosquitoes which are the parasite's vector (you can read a previous post about toxic birds and their lice here and a post about bees protecting themselves against fungal parasites by lining their hives with resin here).

Photo of Culex pipiens
by Joaquim Alves Gaspar

One of the aspects of parasites that people tend to find a little more disturbing is the idea that they can control the minds of other animals. Although this may seem like the stuff of science fiction, this is indeed sometimes the case. For those parasites that live inside other animals, there are often several stages to their lives and each of these stages may require the use of a different type of animal. This presents a challenge in getting from one animal to the next and so if a parasite can influence the behaviour of one animal in some way, making it easier to reach the next, this is incredibly advantageous.

Many parasites have evolved abilities to do just this. For example, some blood-sucking insects infected with certain parasites are known to bite more frequently than when uninfected, helping to spread the disease to more animals. This is seen in malaria-infected mosquitoes, tsetse flies infected with sleeping sickness, and plague-infected fleas. But is it possible that a parasite can also influence a healthy, uninfected animal’s behaviour? The paper featured today attempts to address this question. Researchers used a species of avian malaria (Plasmodium relictum - a parasite that has been previously covered on the blog by this post here) and its natural mosquito carrier (Culex pipiens) to find out if malaria-infected animals are more attractive to mosquitoes than healthy, uninfected animals. This species of malaria is spread among birds via its mosquito carriers and thus the researchers chose canaries to carry out the experiment.

Photo of canaries by 3268zauber

Pairs of canaries, one infected with the parasite and one uninfected, were exposed to uninfected mosquitoes to see which bird they would prefer to feed on. The mosquitoes mostly fed on only one animal per sitting, so the blood inside their bellies could be removed and the DNA analysed to determine which bird it fed upon. The experiment was carried out on the day the birds were injected with the parasite, as well as 10 days and 24 days after injection, so as to monitor any changes as the parasites matured inside them.

From this experiment the researchers discovered that, not only did the mosquitoes clearly prefer to feast on the malaria-infected canaries, but also this behaviour became more prominent as the malaria parasites mature within the canary and become capable of crossing into a mosquito. The researchers suggest that the malaria parasite influences the mosquito’s decision to feed on the infected animal, assisting its transfer to said mosquito – the next stage in its life-cycle. The mechanism used to achieve this has not yet been determined but the researchers suggest that the parasite may alter the odours that are emitted from the host animal, enticing the mosquitoes to choose its infected animal over other uninfected animals. If these odours can be identified and reproduced, they may prove very useful in control of malaria in the future, for example in mosquito traps.

So is this an example of crazy sci-fi mind-controlling by parasites? Ok, so mosquitoes may not exactly be renowned for their calculated decision making skills. But the results of this experiment were still able to show us how the malaria parasite can influence a healthy mosquito’s decisions, offering further insight into the awesome manipulative powers of parasites.

Reference
Cornet S, Nicot A, Rivero A, & Gandon S (2013) Malaria infection increases bird attractiveness to uninfected mosquitoes. Ecology Letters 16: 323 – 329.

This post was written by David Rex Mitchell

Macrodasyceras hirsutum

On this blog, we have featured many parasites that drastically alter the appearance and/or behaviour of their host, usually to make them more likely to be eaten by the next host in the parasite's life-cycle. But today, we are featuring a parasite that makes their hosts appear less appetising - a seed parasitoid that has other plans for its host - none of which involves being eaten.

From the perspective of the plants that produce them, fruits are a way to turn animals into willing seed couriers. By wrapping seeds up in a tasty package, plants can deposit their seeds temporarily inside the body of an animal that will carry them off to a new location. We have even featured a (parasitic of course) plant on this blog that uses beetles for such a purpose.

photo from Figure 1 of the paper

Unlike the rest of the plant, which is often indigestible and laden with defensive toxins, the fruit is supposed to be attractive and appetising to would-be animal dispersers. However seed parasitoids such as Macrodasyceras hirsute have other plans for the fruits - they do not care for the fruit's flesh - they are only after the nutritious seed. Unlike the parasite we featured in the last post, the gullet of a bird is a death sentence for the larvae of this parasitoid (though as always in nature, there are some exceptions), which is a bit of an inconvenience as the fruits it parasitises are meant to be eaten by birds.

Macrodasyceras hirsutum parasitises the fruit of the mochi tree Ilex integra and all it wants to do is to live out its larval stage munching on seeds and grow up to be a wasp. It would rather not have its life suddenly interrupted by a hungry bird feasting on the mochi tree's bright red ripe berries.

So to ensure that its home will not end up tumbling down the throat of a bird, M. hirsutum larvae counteract the berry's usual ripening process, and ensure that it stays green (and unappetising to birds, which disdain unripe berries). A team of Japanese scientists found that if they shielded the fruits from wasp attack, almost all the mochi berries ripened to red. But, if they are exposed to M. hirsutum, some of them stayed green, and all the berries that stayed green had M. hirsutum larvae living inside them. Furthermore, they found that the more larvae there are in the berry, the more intensely green the fruit becomes - M. hirsutum did not merely stop the berries turning from green to red, they actually turned the dial on the green tone all the way up.

This little wasp is not the only insect to do this. Holly berries infected with a species of midge also stay green. It is unknown how this wasp interferes with the berry's pigment production/development, though for the holly berry midge it has been suggested that a symbiotic fungi is responsible for maintaining the host fruit's green colour. The relationship between fruit-bearing plants and fruit-eating animals has evolved to be a mutually beneficial interaction whereby one party provides food (fruits) while the other returns with a service (seed dispersal). But, the actions of M. hirsutum and other such seed parasitoids tinkering away in the background can certainly undermine the effectiveness of this mutualistic partnership if they cause otherwise ripened fruits to go uneaten. The extent of the impact such seed parasitoids have on the ecology and evolution of such plant-animal interaction is currently unknown.

Reference:
Takagi, E., Iguchi, K., Suzuki, M. and Togashi, K. (2012) A seed parasitoid wasp prevents berries from changing their colour, reducing their attractiveness to frugivorous birds. Ecological Entomology 37: 99-107.

Apocephalus borealis

Many of you have heard of the very scary phenomenon called "Colony Collapse Disorder" - and if you haven't, you should, because it could be a major threat to the food we eat. CCD is when the worker honey bees abandon their hives and die, which, if widespread, can mean drastic decreases in pollination of crops. This phenomenon was first reported in the U.S. in 2006 and ever since that time, scientists have struggled to uncover what was responsible. Everything from cell phone radiation to genetically modified crops to a variety of parasites of honey bees were suggested to be the cause. Then, today, a new paper in PLoS One showed data suggesting that another kind of parasite is linked to CCD. Apocephalus borealis is a parasitoid fly that was known to attack bumblebees and paper wasps, but now has been demonstrated to also attack honeybees in the U.S. - in fact, 77% of the colonies sampled near San Francisco were parasitized by A. borealis. The authors used DNA barcoding to confirm that the flies in the honey bees were genetically indistinguishable from those parasitizing bumble bees.

The authors of the new study also found that bees that were found flying around at night (something honey bees don't normally do) were significantly more likely to be parasitized by the fly and furthermore, the sick bees also seemed disoriented. It is not currently known whether or not the tendency for the parasitized bees to fly at night away from their colonies is another example of manipulation of the host by a parasite or whether this might be an act of altruism by the bee, carrying its parasite away from its colony and thus protecting the others.

Although these new results are very exciting, many questions remain to be answered about the history and impact of A. borealis. First, when did the switch into honey bees occur? Honey bees are not native to the U.S., but since they are so well monitored and studied, the authors believe that the switch must have happened recently - otherwise it would have been noticed by apiculturists. Second, could these flies also be serving as vectors for other bee pathogens? Two known bee pathogens, Deformed Wing Virus and Nosema ceranae, a microsporidian were found in the A. borealis flies. And finally, could the invasion of honey bees by this parasite mean that CCD is going to increase? The natural hosts of A. borealis are bumble bees, which live in small colonies where only the queen herself survives the winter, but honey bee colonies have thousands of bees and their activity maintains some amount of heat, even in colder winter months. This increase in host resources and more generations per year could spell a population explosion of A. borealis...and that won't be good for those of us who depend on pollination - like all of us.

The image is from the paper. Look closely at the abdomen of the bee - that's a little parasitic fly laying eggs into it. Soon the larvae will emerge from the dead host. (You can see a photo of this in the original paper as well.)

Source: Core A, Runckel C, Ivers J, Quock C, Siapno T, et al. (2012) A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis. PLoS ONE 7(1): e29639. doi:10.1371/journal.pone.0029639.

Ophiocordyceps unilateralis

Have you ever been so intoxicated that you start walking erratically, stumble away from your friends, stagger around in circles, clamber onto things that you wouldn't normally be seen near, and the next thing you know, you are strapped down in unfamiliar surroundings, unable to extricate yourself? Well, that pretty much describe what happens to ants which become infected with the famous "zombie ant" fungus - Ophiocordyceps unilateralis.

Much has been written about this famous fungus which turns ants into zombies - it is a parasite which captures the same part of our psyche as the monstrosities of horror movies, and there is evidence to suggest that these fungi have been tormenting ants for at least tens of millions of years. But despite all that attention, few people have actually witnessed or documented the sequence of behaviour leading up to the infected ant's paralysis and death. But in a paper published this year, a group of researchers followed the behaviour of ants infected with the famous "zombie"-inducing fungus and compare them to their uninfected brethren.

They noticed a few peculiarities with the behavioural repertoire of infected ants which stood out. While healthy ants studiously stick to the usual lanes of ant traffic, climbing into the canopy to forage with all the other busy worker ants, "zombie ants" are loners which meander around in the understory by themselves, are unresponsive to most stimuli, and frequently stumble and fall from the branches they are walking on. Essentially, the ants act absolutely drunk, indeed, the researchers described the behaviour of the "zombie ants" as a "drunkard's walk" in their paper. Another weird thing that infected ants start doing is their tendency to crawl all over and bite into leaves - something which healthy ants don't tend to do. There's a good reason why the fungus steers the ant towards leaves and afflict it with this oral fixation - it is preparing it for the next step in the fungus' development.

For the fungus to successfully reproduce, the ant must die - but it must die in a particular position to maximise the viability and dispersal of the fungal spores, specifically in the humid understory, hanging from the underside of a leaf, about 25 cm (about 10 inches) above the ground. But once the fungus maneuver the ant into position, how does it get the host to comply and stay there? The researchers made fine histological cross-section of the infected ant's head and found that once the fungus has made the ant locks its mandible in place, it busily gets to work dissolving the muscles which control those mandibles, ensuring that the ant will be locked in a death grip forevermore. A few days after the ant dies while gripping onto, the fungal stalk emerges from the head of the ant, ready to spray its spores down to the soil below to create more drunken "zombie ants".

Image from the Wikipedia.

Reference:

Hughes DP, Andersen SB, Hywel-Jones NL, Himaman W, Billen J, Boomsma JJ. (2011) Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection. BMC Ecology 11:13

Postscript: A few hours after I wrote this post, I found out that Carl Zimmer has already written about this study (why, of course! *facepalm*), so if you want to read his version instead, you can see it here.

Allomermis solenopsi

It seems that ants just can't get a break when it comes to parasites. When they are not being persuaded to clamp themsleves to the top of a grass blade for a nightly sacrificial ritual (Dicrocoelium dendriticum), they are doing impersonations of a juicy berry thanks to some worms in their gut (Myrmeconema neotropicum). Today's parasite adds to the insult and takes its ant host for an impromptu swim, then leaves it to drown. Allomermis solenopsi is a nematode from the Mermithidae family, a group of nematodes which have plagued insects for at least 40 million years. While they superficially resemble nematomorph hairworm (e.g. Spinochordodes tellinii) and have a similar life-cycle, these worms actually belong in a separate phylum. However, the mermithid nematodes have convergently evolved the same ability as the hairworms to manipulate their hosts - namely, taking the host for a suicidal trip to the pool. Allomermis solenopsis develops inside the gaster (abdomen) of the ant and when it reaches maturity, it needs to exit into a body of water to mate and lay eggs. Other species of mermithids are well-known for inducing water-seeking behaviour in their hosts, so given that the nematode would dry out very quickly if it becomes exposed to the outside environment, it is likely that when the time comes, A. solenopsi just takes its ant for a terminal dunk.

Image from figure of the paper.

Reference:
Poinar Jr, G.O., Porter, S.D., Tang, S. and Hyman, B.C. (2007) Allomermis solenopsi n. sp. (Nematoda: Mermithidae) parasitising the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) in Argentina. Systematic Parasitology 68: 115-128.

Contributed by Tommy Leung.

September 19 - Phasmarhabditis hermaphrodita

Parasites have to find their hosts and if you're a parasite of gastropods like snails and slugs, that means being attracted to slug slime - i.e. the chemicals found in the mucus secreted by slugs and snails. Phasmarhabditis hermaphrodita is a parasitic nematode that infects and kills its molluscan hosts and has, in fact, been shown to be attracted to their mucus. These parasites are commercially sold as slug pest control agents in the U.K. Other studies have shown that the parasites are somehow able to manipulate the behavior of their hosts to crawl into the soil -this allows the nematodes to complete their development before the dead slug or snail or consumed by a scavenger.

Image is from this site.

August 10 - Dicrocoelium dendriticum

Dicrocoelium dendriticum, better known as the lancet fluke, is a species of fluke that lives in the liver of grazing mammals such as sheep. Like most flukes, it has a 3 host life-cycle, the adult worm living inside the sheep, lay eggs which are shed into the environment with the sheep's faeces. The first intermediate host for this parasite are terrestrial snails which become infected by accidentally ingesting the parasite's eggs. The parasite undergoes clonal replication inside the snail, producing hundreds of infective larvae which are then packaged into slime balls and extruded into the environment. For some reason, these slimeballs are eagerly gobbled up by ants which are the parasite's second intermediate host.

Now sheep are not known for including ants as a significant part of their diet, so how is D. dendriticum supposed to get itself into a sheep through an ant? It does that by taking control and setting its ant host up for a rendezvous every evening. Once infected, the ant begins to behave very oddly indeed. As dusk falls, it would crawl up a blade of grass until it reaches the tip, then firmly clamps itself into that position with its mandible for the entire evening. The infected ant would perform this peculiar routine every night, but as the sun rises, it would resume its usual activities - assuming that it has survived the evening and not been incidentally ingested by a hungry sheep. By inducing this peculiar behavioural pattern in the ant host, D. dendriticum brings itself (through the ant) within the vicinity of a grazing sheep, thus setting up an encounter which otherwise would not have occurred, allowing it to complete its seemingly obtruse life-cycle.

Check out the very funny cartoon version of this life cycle here.

Contributed by Tommy Leung and thanks to Craig Carlough (Lancaster, PA) for sending along the Oatmeal comic.

August 9 - Schistocephalus solidus

Schistocephalus solidus is a tapeworm with a three-host life cycle. Free-swimming coracidia are eaten by copepods, the first host. After about 2 weeks of development in copepods, the worm is ready to be transmitted to the second intermediate host, three-spined sticklebacks. In the fish host, the worm grows to gargantuan sizes; in exceptional cases it can even weigh more than the host. Fish are impacted in various ways by infection, showing altered behaviours (risk-taking, flight response, etc.), brain chemistry, and immune responses. These modifications are thought to lead to a higher transmission rate of the parasite to its final host, fish-eating birds. Within 48 hrs of reaching the intestine of the final host, the parasite is reproductively mature and producing eggs. After about a week, the worm has produced all its eggs and dies. This short and explosive reproductive period is presumably the reason why S. solidus is one of the few helminths that can be bred in vitro.

Contributed by Daniel Benesh.

March 31 - Spinochordodes tellinii

Ever seen a grasshopper jump into a pool? Probably not. The reason is normal, healthy individuals would never take a dive to almost certain death. Spindochordodes tellinii on the other hand, has different intentions. This parasitic nematomorph hairworm is able to override the grasshopper’s instinct to stay out of water. Spindochordodes tellinii larvae are consumed by grasshoppers or crickets and develop inside their hosts. The hairworm can grow to enormous lengths yet allow the grasshopper or cricket to stay alive. The exact process S. tellinii uses to manipulate its host is still largely unknown. We do know that the parasite produces proteins that affect the central nervous system and that infected grasshoppers/crickets also produce different proteins in their brains which healthy individuals do not. Mature adult S. tellinii use their abilities to force their host to jump into some body of water allowing the parasite to escape to find a mate. Understanding how parasites can manipulate behaviors of other organisms may help us to further understand human behavior-system links.

See: Bhattacharya, S. 2005. Parasites brainwash grasshoppers into death dive.

Contributed by Zander Crawford, Bucknell University.

March 21 - Plagiorhynchus cylindraceus

Often times endoparasites will alter the behavior of a host to complete their lifecycles. The acanthocephalan, Plagiorhynchus cylindraceus, is a common parasite of songbirds in North America, typically robins (Turdus migratorius) or Europeans starlings (Sturnus vulgaris). While inside the bird, the worm produces eggs that pass out in the bird’s feces and are consumed by pillbugs (Armadillidium vulgare, shown in photo), the main intermediate host. This worm is capable of activating a suicidal behavior in the pillbugs to propogate its own lifecycle. Once infected with the acanthocephalan, the pillbugs become more active and frequent uncovered, light-colored areas on the forest floor while avoiding hiding underneath objects, such as leaves. By exposing themselves, the pillbugs are more likely to be eaten by a predator, such as robins or starlings. Once consumed by the bird the worm is free to reproduce, thus completing its lifecycle. Pillbugs are not the only animals to become infected with this worm. Some North American shrews (Soricidae) have been found with these worms encapsulated in their intestinal mesenteries, although this becomes a dead-end for the parasite because it cannot be passed on to a songbird from the shrew’s intestines. The proboscis of this parasite has many hooks that it imbeds in the host’s intestinal walls and prevent it from passing through with a host’s meal. Nutrients from such a meal are absorbed through the body surfaces of the parasite; the only way the worm receives nutrition since it lacks a gut tract.

Contributed by Anna Phillips.

March 9 - Moniliformis moniliformis

Moniliformis moniliformis is an acanthocephalan, or thorny-headed worm. Like others in this group. M. moniliformis alternates between two hosts. The first is usually an insect such as a cockroach or a beetle, and then the definitive host is often a rodent such as a mouse or rat. Janice Moore and colleagues have used M. moniliformis to conduct a variety of studies on the manipulation of host behavior and have found that some cockroaches that are infected with M. moniliformis move more slowly, though other cockroach species do not have detectable changes in behavior. Humans can become infected if they ingest the intermediate hosts accidentally (but so far there is no evidence that they turn into couch potatoes who like dark rooms.)

February 27 - Myrmeconema neotropicum

Yesterday, the parasite was saving coffee berries, today the parasite is making ants look like berries. Myrmeconema neotropicum is another nematode parasite that infects the ant, Cephalotes atratus in South America. The life cycle is somewhat similar to that of yesterday's parasite. Foraging ants pick up the nematode's eggs which have been shed in bird feces and feed them to their larvae. Inside the ant pupa, the worms hatch, mature and mate. As the embryos inside the female nematode mature, the gaster, or abdomen of the ant, swells and goes from being black, to translucent, to bright red. Adult ants then walk around with bright red abdomens held up into the air and are also slower and "clumsier" - perfect targets for frugivorous birds. The species, described in 2008, also changed the taxonomy of the ant hosts. Over a century before, a variety of tropical ants had been described based on their unusual red abdomens. We now know that they were just parasitized individuals. Makes me wonder how many other "species" have been erected based on parasite-induced morphological changes...

Image from figure of the paper.

You can read the original paper here.

January 15 - Curtuteria australis

Curtuteria australis Allison 1979 (Platyhelimthes: Digenea: Echinostomatidae) infects bivalves (in this case, a cockle, a type of clam) on the mudflats and sandflats of New Zealand. This parasite lodges itself in the foot of the bivalves where it forms a hard cyst. As more and more parasites accumulate, the cockle loses its ability to dig itself into the underlying sediment, leaving it stranded on the surface of the mudflat/sandflat. There, it is exposed to predation by shorebirds such as oystercatchers, which are the parasites' next hosts. These parasites also have a cascading effect on the rest of the ecosystem - as the mudflat is filled with stranded bivalves, the nature of the substrate changes from one consisting largely of mud and sand, to one littered with the hard shells of bivalves. This, in turn, alters the biotic community which inhabits the rest of the ecosystem.

The photo shows a cockle's foot with encysted metacercariae of Curtuteria australis tagged with a fluorescent dye.

Contributed by Tommy Leung.
Read the full paper here.

January 9 - Toxoplasma gondii

Blame it on the cat. Or the raw meat. Exposure to either can result in infection with Toxoplasma gondii. Distant relatives of Plasmodium, the parasites that cause malaria, T. gondii often doesn't show many symptoms in its host. Immunocompromised patients and fetuses of pregnant women who become infected can be at high risk from more serious complications. Recently, data have shown that people infected with T. gondii show behavioral changes, too - with differences between sexes. Men with T. gondii are more aggressive, while women seem more intelligent! Another case of parasite manipulation?

January 7 - Sacculina carcini

A great example of a crustacean that parasitizes another crustacean is the barnacle, Sacculina carcini, which is a parasite of crabs. These parasites are favorites of professors as they represent a great example of host manipulation. Sacculina mimics the broods of female crabs, causing her to groom the parasite sac and help the eggs disperse into the water. And if the Sacculina finds itself in a male crab - it just sterilizes it and causes it to act like a female!

January 2 - Leucochloridium paradoxum

Ever feel like you're just not quite in control? Try being a snail infected with Leucochloridium paradoxum Carus 1835 (Platyhelminthes: Strigeidida). These trematode parasites alternate between snails, their intermediate hosts, and birds, the definitive hosts. The parasites invade the tentacles of the snails, causing them to look like caterpillars (see photo, which shows a normal and an invaded tentacle), which makes them attractive to birds.