"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

June 26, 2015

Lysibia nana

Lysibia nana photo by Nina Fatouros
Used with permission
from
BugsinthePicture 
In order to live, a parasite must find its host. Whereas some parasites take a passive approach and simply wait for a chance encounter, many species are more proactive. In the case of parasitoid insects that have free-flying adults, they have various adaptations for tracking down their hosts. But what about the hyperparasites - parasites that infect other parasites? How do they find their host, which themselves are hidden within the body of a host animal? It seems as if they would need to have X-ray vision in order to complete their life cycle.

The parasite we are featuring today is Lysibia nana, a hyperparasitoid that infects Cotesia glomerata - the parasitoid wasp which lays its eggs inside caterpillars. It turns out that L. nana does not rely on superpowers like X-ray vision, but a far more parsimonious ability. To find out how L. nana finds a host, first of all, we have to ask; how does C. glomerata itself find its hosts? A few months ago, we featured a parasitoid fly that uses sound to track down its prey, but most parasitoid wasps use scent to sniff our their hosts. But this scent does not come directly from the host itself, but rather, the host's food.

When a plant comes under attack by herbivores like caterpillars, they emit volatile chemical signals call kairomones that acts like a dinner bell for parasitoid wasps, which have evolved to use those chemicals to guide them to their prey. Feeding by different species of caterpillars elicit different chemical emissions from the plant, which provides a signature of their presence and attract different species of parasitoids.

Parasitoid wasps are master body-snatchers, they don't just consume their hosts from within; while they are in residence they also change the caterpillar's physiology, altering its growth pattern and behaviour - so much so that on some levels the parasitised caterpillar can be considered as almost a different animal. But they have their own enemies in the form of hyperparasitoids like L. nana.

A research group in the Netherlands conducted a series of experiments to figure out how this hyperparasitoid tracks down its hidden prey. They first tested how wild cabbage plants responded when they come under attack by two different species of caterpillar - Pieris brassicae and P. rapae.
Dead caterpillar with Cotesia glomerata cocoons
Photo by Hectonichus
They found that two caterpillars induce very different blends of chemical volatiles from the plant. But it is a different story when those caterpillars are parasitised by C. glomerata. The physiological alteration that the parasitoid imposed on their host was reflected in how the caterpillar's food plant responded. Cotesia glomerata manipulated their hosts to such a degree that once parastisied, both P. brassicae and P. rapae elicited a far more similar blends of chemical emissions from the plant.

This is where the hyperparasitoid L. nana comes in. The researchers put some female hyperparasitoids in a Y-maze and exposed them to combinations of different volatile chemical released by; caterpillar-free plants, plants which had been chewed on by caterpillars, or plants which have been chewed on by parasitised caterpillars. They noticed that given the choice between the chemicals of plants damaged by parasitoid-free and parasitised caterpillars, the hyperparasitoids preferred overwhelming to go in the direction of the latter - regardless of what species the host caterpillar might be. To L. nana, whether those caterpillars had parasitoid babies onboard is far more important than their species identity, and they showed no clear preference for either caterpillar species as long as they were parasitised by C. glomerata.

The researchers also conducted a field-based study that corroborated the results from the behavioural experiment. They did so by attaching C. glomerata cocoons to some wild cabbage plants that they have grown in an experimental plot. Some of the plants had previously been munched on by parasitoid-free caterpillars, others by parasitised caterpillars. After 5 days, they checked the parasitoid wasp cocoons for signs of L. nana and found that cocoons on plants which have been chewed on by parasitised caterpillar attracted far more L. nana than those munched on by parasitoid-free-caterpillars

So while parasitoid wasps like C. glomerata may have masterful control over their host body's physiology, this also leaves a calling card to their own hyperparasitoids. For the hyperparasitoids, it's what's inside that counts.

Reference:
Zhu, F., Broekgaarden, C., Weldegergis, B. T., Harvey, J. A., Vosman, B., Dicke, M., & Poelman, E. H. (2015). Parasitism overrides herbivore identity allowing hyperparasitoids to locate their parasitoid host using herbivore‐induced plant volatiles. Molecular Ecology 24: 2886–2899.

P.S. I will be attending the New Zealand Society for Parasitology and Australian Society for Parasitology joint conference in Auckland, New Zealand. So watch for tweets with highlights from conference at my Twitter @The_Episiarch! All tweets related to that conference will have the #NZASP15 hashtag.

June 12, 2015

Coccipolipus hippodamiae

Today we feature a guest post by Katie O'Dwyer who recently completed her PhD at the Evolutionary and Ecological Parasitology group at Otago University. She has previously written for Parasite of the Day about  Phronima - a parasitic crustacean that turns gelatinous salps into floating zombies. This time she has written a story about why "Promiscuous ladybirds pay the price when it comes to parasites".

A pair of mating two-spot ladybirds (photo by Richard001)
For most of us when we hear any mention of sexually transmitted infections (STIs) we think of humans, herpes and the variety of public service announcements we see about practicing safe methods in order to avoid contracting STIs. However STIs are rife in the animal kingdom. They can be found in any animals that require internal fertilisation for reproduction. And it seems that one group which can really benefit from advice on safe methods to avoid STIs are the ladybirds.

Who would have known (well, probably some entomologists) that these beautiful beetles are highly promiscuous and not very choosy about who they mate with? This makes them an extremely efficient host for any sexually transmitted parasite. Today’s post is about a sexually transmitted mite Coccipolipus hippodamiae and its host - an European ladybird.

These mites are transmitted when ladybirds are mating and they migrate to the wing case (called elytra) of the beetles. Here they latch on using their mouthparts and feed on the hosts blood (known as haemolymph) before metamorphosing into adults. What quickly follows is the development of a large mite colony on a single ladybird. The presence of these mites can reduce the fertility and reproductive capacity of female ladybirds.

A female Coccipolipus hippodamiae mite with eggs.
Scale bar = 100 µm (photo from here)
There are some measures that can be taken when faced with high levels of STIs, such as switching the mating system to monogamy and being choosier when it comes to potential partners. However, studies have found no evidence for C. hippodamiae having any effects on mate choice in ladybirds. Luckily for the mites, female ladybirds are unable to detect if their male partners are infected.

However, there are other factors that limit the success of these parasites. Timing is an important aspect of STI transmission in this system. Ladybirds overwinter and refrain from mating regularly during this season. Following the period of overwintering, these highly promiscuous bugs travel across plants on a mating spree, hooking up indiscriminately, and triggering an epidemic of mite infections. A key aspect in this process is the overlap between generations.  In order for the mite population to be maintained mating must occur between consecutive generations of ladybirds. The mites have evolved to take advantage of those hosts with overlapping generations and unfortunately for the two-spot ladybird, Adalia bipunctata, it has one of the longest periods of overlap between generations. Therefore it is also the most common host for these mites.

These miniature mites have also adapted to infect other ladybird species with up to four species of European ladybirds in its repertoire of hosts. Interestingly, one of these ladybird species does not have an overlap in generations because a period of diapause is required during development, whereby one generation dies off before the next one metamorphoses into adults.  Luckily for the mite, these ladybirds appear free and easy when it comes to mating, even across different species. So even this ladybird species without overlapping generations can become reinfected during such hybrid mating sessions.

This picture gets even more complicated when the invasive Asian harlequin ladybird gets involved. This beetle has invaded the UK and is out-competing the native ladybirds (of which there are up to 46 species!). As a method of control some researchers have decided it might be a good idea to introduce the mites as a biological control agent. However, up to now, C. hippodamiae has not been found in ladybirds in the UK as they do not overlap in generations in the same way that continental European ladybirds do. This is currently an active area of research and not much is known about the effect the mites could have on the UK’s naïve ladybird hosts. In their struggle against the feisty harlequin ladybird, can a foe of European ladybirds become a friend of the UK’s native ladybirds? Only further research will tell…

References:

Hurst, G.D.D., Sharpe, R.G., Broomfield, A.H., Walker, L.E., Majerus, T.M.O., Zakharov, I.A., Majerus, M.E.N. (1995) Sexually transmitted disease in a promiscuous insect, Adalia bipunctata. Ecological Entomology 20, 230-236

Webberley, K.M., Hurst, G.D.D., Husband, R.W., Schulenberg, J.H.G.V.D., Sloggett, J.J., Isham, V., Buszko, J., Majerus, M.E.N. (2004) Host reproduction and a sexually transmitted disease: causes and consequences of Coccipolipus hippodamiae distribution on coccinellid beetles. Journal of Animal Ecology 73, 1-10

Rhule, E.L., Majerus, M.E.N., Jiggins, F.M., Ware, R.L. (2010) Potential role of the sexually transmitted mite Coccipolipus hippodamiae in controlling populations of the invasive ladybird Harmonia axyridis. Biological Control 53, 243-247

Post written by Katie O'Dwyer

May 29, 2015

Mermis nigrescens

Photo by Haseeb Randhawa & Ken Miller here
New Zealand is a land known for its unique animals and plants, but over the centuries it has also become home to many introduced species which have become invasive and disruptive to its natural ecology. While many of the introduced species are recognisable larger animals such as pigs, possums, and rats, some of them tiny creepy-crawlies - insects and other invertebrates. And some of those have passengers living inside them which have largely been hidden out of sight

Meet Mermis nigrescens, a nematode worm which arrived in New Zealand inside European earwigs (Forficula auricularia). Mermis nigrescens is a species which had been known since 1842, and it is likely that it might have even been discovered earlier than that in 1766, but was mistakenly identified as Gordius - a genus of hairworm - which despite superficial resemblance and a similar life cycle, belongs to a different phylum. Its host, the European earwig, first arrived in New Zealand during the 19th century, but it was only recently noticed that these insects have also brought along a parasite from their original home range.

Photo of earwig host with M. nigrescens from this paper
Like other nematodes from the family Mermithidae, M. nigrescens are aquatic as adults and only parasitise earwigs during their juvenile stage. An earwig can be hosting anything from a single worm up to as many as seven of those parasite. When M. nigrescens reaches maturity, it needs to get into a water body to mate and reproduce. And if they're anything like the hairworms and other species of mermithids, it would commandeer the earwig and steer it to water, where the worm can evacuate its host xenomorph-style and leaves the now hollowed-out earwig to drown.

So how do we know this parasite is an introduced species and isn't one that the earwig had simply acquired in its new home?

Molecular analysis looking at three genetic markers from M. nigrescens showed that the closest relatives of these particular nematodes are found in Canada - M. nigrescens appears to be well-travelled, and is found all over the world. But it does not seem to be as abundant in Dunedin, New Zealand as seen elsewhere in world. In the population that was examined for this study, only 19 out of the 198 earwigs examined were infected with M. nigrescens, whereas a study in Tasmania, Australia found the parasite in half of the earwigs examined, and it was even more common in Ontario, Canada where infection prevalence reached 63%. It is currently unknown why M. nigrescens does not seem to be as abundant in New Zealand as it is elsewhere in the world, though it could just be something about this particular bunch of earwigs and that there are more heavily parasitised earwig populations elsewhere in New Zealand.

But where did the M. nigrescens population in New Zealand originate? While its closest living relatives are found in Canada, did it arrive to New Zealand from there? After all, the original home of M. nigrescens is Europe, so the Canadian population was not native to that region either. The missing piece of this puzzle is genetic sequences of M. nigrescens specimen from its original range in Europe, which might resolve where this newly discovered New Zealand population originated - from Europe or elsewhere. For all we known, this supposedly widespread species may in fact be composed of a complex of closely-related cryptic species, with each species found in a different region of the world.

Just goes to show that even in the common earwig, there are natural history secrets waiting to be revealed.

Reference:
Presswell, B., S. Evans, R. Poulin, and F. Jorge. 2015. Morphological and molecular characterization of Mermis nigrescens Dujardin, 1842 (Nematoda: Mermithidae) parasitizing the introduced European earwig (Dermaptera: Forficulidae) in New Zealand. Journal of Helminthology 89: 267-27

May 15, 2015

Taenia serialis

Many parasite can cause health problems for their hosts, but aside from those that infect humans and domestic animals, it is not entirely clear just how much impact most parasites are having on the host population. Of course, the problems caused by parasites for a host goes beyond direct pathology; for social animals, parasitism can also affect how individuals interact within a group.

(A) Frodo the gelada and (B) the T. serialis larvae that spilled from her back
Photo from Fig 1 of the paper
In this post, we will be discussing a study which investigated the impact of a tapeworm on a population of gelada baboons (Theropithecus gelada) in Ethiopia. The tapeworm in question is Taenia serialis, which is related to some more well-known species of tapeworms include the beef tapeworm and the pork tapeworm. Despite being commonly used in first year biology textbook as a "typical" example of a tapeworm, Taenia is anything but typical in terms of its life cycle compared with most other tapeworms.

Like other parasites that have a complex life cycle, the larval stage dwells in an animal known as the intermediate host - this is where the parasite grows to a certain size before being eaten by a predatory animal which serves as the final host (definitive host), where it will mature into a sexually reproducing adult worm. Taenia does something different in its intermediate host - an adaptation found in the evolutionary play book of the digenean flukes and some other parasites. Instead of merely growing larger and await consumption by the final host, they asexually multiply inside the intermediate host - making many genetically identical copies of themselves and forming cysts which contain hundreds or even thousands of larval clones.

As you can imagine, having a slowly growing bag of worms lodge inside your body is not good for your health (it actually served as a plot device in an episode of House), but just how much does it impact a population of wild animals? The paper featured today is the result of a long term study stretching from January 2007 to June 2013 monitoring the health and demographic data of 16 gelada bands on the Guassa Plateau located on the western edge of the Great Rift Valley on the Ethiopian Highlands. The research group kept track of 348 individual geladas over the course of the six and a half year study, noting their health, reproductive status, and any birth or death. These monkeys are also commonly infected by a species of Taenia which uses the geladas as an intermediate host.

The final host for this parasite is most likely the Ethiopian Wolf (Canis simensis) - which shares the same habitat with the geladas. Even though this carnivore usually only hunt small mammals such as rodents, they are known to scavenge on gelada corpses - which is probably how they become infected with T. serialis. When geladas accidentally ingest tapeworm eggs which had come from the wolf's faece, the parasite proliferate in the monkey, forming cysts or bladdders which can become visible as protrusions on the skin. While the cysts are grotesque, this allows researchers to monitor infections in the monkeys without coming into direct contact them (which might affect their natural behaviour). But while the cysts are clearly recognisable on the gelada's skin, one cannot simply identify a parasite via skin cysts alone - a closer examination is necessary.

Fortuitously (for science anyway), during the course of their study they were able to obtain some parasite material for identification due to a serendipitous event. Some members of the research group noticed an adult female gelada they named Frodo had a large parasite cyst on her back. At some point, the cyst ruptured and spilled out a bunch of parasite larvae, enabling the researchers who were following Frodo at the time to collect some of the parasites for examination, and subsequently identify them as T. serialis. While this tapeworm is usually known to infect rabbits as an intermediate host, on the Ethiopian Highlands, they infect geladas.

Overall, the researchers found that one in six of the monkeys they monitored had at least one T. serialis cysts, and most of those afflicted were adults with one-third of the adult population showing signs of infection by the tapeworm at some point. Those infected monkeys are more than twice as likely to die than their uninfected comrades, and this tapeworm's impact extends beyond the individual directly infected with it. Infants born to tapeworm-infected mothers are twice as likely to die before their first birthday compared with infants that have mothers with no signs of infection, and infected female monkeys also experience a longer lag period between the birth of each offspring.

Male monkeys also lose out due to T. serialis infection - geladas are polygamous species that organise themselves into so-called one-male units (OMU), each consisting of a single male with a harem of females. The researchers observed that tapeworms infection compromises the male monkeys' ability to hang on to their harems and infected geladas are more likely to lose in a dispute with any new (uninfected) challenger(s) that appear on the scene.

The impact of parasites on most wildlife is not well-understood, and often their effects are not immediately visible without a sustained long-term ecological and demographic study. Even natural levels of infection can have profound impact on host population, as seen with the effects of T. serialis on geladas. Therefore when it comes to wildlife conservation, it important to be mindful of parasites and the hidden role they play on the stage of nature.

Reference:
Nguyen, N. et al. (2015). Fitness impacts of tapeworm parasitism on wild gelada monkeys at Guassa, Ethiopia. American Journal of Primatology 77: 579-594.

April 26, 2015

Nepinnotheres novaezelandiae

Life as a pea crab seems pretty sweet, you spend most of your time sitting snug and protected within the armoured shelter of a shellfish, while your host's filtration current bring you a constant stream of oxygen and food - everything that a pea crab needs for a good life. Well, almost everything - because there's more to life than just being protected and fed. Much like other organisms pea crabs need to reproduce - that's how evolution works, and unlike many other living things, a pea crab cannot just clone itself.
Male Nepinnotheres novaezelandiae squeezing in between
the valves of a mussel. From video here.
So when it comes to reproduction, the balance of living the pea crab life tips from "pretty sweet" to "absolutely terrible" - especially if you are a male pea crab. For them, trying to find a mate is a harrowing challenge than none of us can possibly imagine. First of all, to reach a potential mate, you have to leave your host, which means you have to pass the gates that are the valves of the host mussel, without being caught in between them. At that stage, those valves that had offer such formidable protection for the pea crabs then become death traps, with about 13% of male crabs meeting their end at this molluscan gate - their bodies litter the mussel bed.


Once outside, the male pea crab faces even more challenges. These tiny crustaceans, which are more accustom to a cosy life inside a shellfish, have to cross the treacherous, open areas of the mussel bed, filled with horrible monsters (in the form of predators like fish, octopus, and larger crustaceans) for which an exposed pea crab is just a convenient snack. Furthermore, male crabs only make up 20% of the population despite the more or less equal sex ratio of immature pea crabs. The length that they have to go to just to find a mate probably has something to do with that...

Despite the odds, almost 90% of all female crabs in the population carry fertilised eggs, so some male crabs must be having successes - but how?

The researchers who conducted this study noticed that the male pea crabs always set out under the cover of darkness when they will be less likely to be spotted by predators, and also because mussels are more relaxed at night. From the researchers' perspective, this also means that all the experiments and observation of pea crab behaviour had to be done in the dark. So in addition to sea water tanks, they set up some infra-red cameras to capture footages of all this activity - like some kind of voyeuristic shellfish reality TV show.

So what would coax a male crab out of his cosy home? To find out, the researchers constructed a flow-through observation chamber lined with PVC tubes in which they placed pea crab-infected mussels. When they placed a mussel with a female crab upstream of one with a male pea crab, the male crab would exit their host 60% of the time, roused into action by something which seem to secreted by the mussel (or the female crab in the mussel) upstream.

Male Nepinnotheres novaezelandiae tickling the mantle edge
of a mussel. From videos here.
The crab then makes its way to the mussel where the female crab resides. Once there, the pea crab patiently tickles the mussel's mantle fringe with its legs to try and convince the bivalve to let it enter. This is also the reason why the male crab only do this at night, because a mussel's response to such tickling can be very different in daylight. Try the same trick during the day and the bivalves would slam shut, crushing the amorous crab between its valves. On average, the crab will spend over three hours fiddling away at the mussel to coax the shellfish into opening up.

Additionally, in a different flow-through seawater tank where the crabs were given more freedom to roam from one host to another, the researchers recorded how long it took for the male pea crab to leave its host and reach a mussel containing a female crab. The entire journey from exiting the original host mussel to reaching their final destination took seven hours on average, though this varies from a quick hour-and-a-half jolt, to an eighteen-and-a-half hour-long trek for one particularly unfortunate individual.

So when love (or at least lust) is in the water, the pea crab will give up the easy life, and risk life and limbs for an evening rendezvous.

Reference:
Trottier, O., & Jeffs, A. G. (2015). Mate locating and access behaviour of the parasitic pea crab, Nepinnotheres novaezelandiae, an important parasite of the mussel Perna canaliculus. Parasite, 22: 13.

April 10, 2015

Edhazardia aedis

When two different parasites find themselves in a small host animal like a mosquito, there is only so much of the host to go around. So there is a pretty good chance that those co-occurring parasites are going to fight it out, and there's no guarantee that there will be a winner out of this conflict.
Photo of E. aedis spores from here

Edhazardia aedis is a microsporidian parasite that specialises on infecting Aedes aegypti - also known as the mosquito that can act as the main vector for a variety of viruses include those that causes degnue fever, yellow fever, and Chikungunya. Edhazardia aedis can spread through the mosquito population via two methods; (1) the parasite can proliferation throughout the mosquito's body until it ultimately overwhelms the host, which dies and dissolves into a cloud of infective spores, or (2) if an infected female mosquito survives the ordeal to adulthood and still manage to produce offspring, her mosquito babies will inherit E. aedis from her (gee, thanks a lot mum!).

But E. aedis can sometimes run into a competing species - Vavraia culicis. It is also a microsporidian, but unlike E. aedis, it is a generalist that can infect many different species of mosquitoes. It is also a mosquito-killer which has the same general modus operandi as E. aedis, where the parasite's spores are released when the host finally succumbs. This study found that mosquito larvae which have less access to food and are infected by both parasites tend to die earlier - and when the host dies, the spores are dispersed for both E. aedis and V. culicis - so everyone wins, right? Well not quite.

While host death does release the spores which allow them to infect more mosquito larvae, the parasites get more spores for their bucks by keeping their host alive for longer - so a host that ends up keeling over too early is not very cost effective. This applies to both E. aedis and V. culicis. Even before host death, the cost of co-infection starts manifesting itself. Regardless of whether the host dies sooner or later, both parasites produce less spores in co-infections. If E. aedis is sharing a host, it produces half as many spores as it would have if it had the host all to itself. But co-infection is even more costly for V. culicis, which manages to produce only a bit over a quarter of the spore it would have in single infections.

It is unknown how these two parasites duke it out in the mosquito, or why E. aedis has a competitive edge over V. culicis. Perhaps by being a specialist of A. aegypti, E. aedis has some sort of home ground advantage when it comes to getting the most out of its host. So it seems that some parasites just don't like sharing, and when it comes to living with others, sometimes it pays for a parasite to be a specialist.

Reference:
Duncan, A. B., Agnew, P., Noel, V., & Michalakis, Y. (2015). The consequences of co-infections for parasite transmission in the mosquito Aedes aegypti. Journal of Animal Ecology 84: 498-508.

March 26, 2015

Emblemasoma erro

During summer the air is filled with the rattling ruckus of cicada songs. Male cicadas produce this summer choir using a pair of noise-making organs located in their abdomen, with the aim of getting attention from any prospective mates. But in some cases, they can also end up with some unwanted attention.

Top: Male Tibicen dorsatus cicada
Bottom: Female Embelmasoma erro fly
Photos from Figure 1 & 2 of this paper
The species we are featuring today is an "acoustically hunting" parasitoid fly - it eavesdrops on the male cicada's flirtatious serenading and uses it to home in on its target. This fly is commonly found on the Great Plains of North America and is a scourge to male cicadas, especially male Tibicen dorsatus.

Most of what is known about such acoustically hunting parasitoids are based on flies from the Tachinidae family - one of which targets crickets (I talked about how crickets on Hawaii evolved to become silent due to the presence of one such parasitoid fly here). But this fly belongs to a different family (Sarcophagidae). Only one species of Emblemasoma is well-studied - E. auditrix- and even though Emblemasoma is widely use in the study of insect hearing, not much is known about how they actually live out in the wild. Until now, the only information available on E. erro are based on two scientific papers - one published in 1981 and the other published in 2009. The paper we are featuring today provides some much-needed update on key aspects of this parasitoid's ecology and life history.

This paper reports on a series of field surveys and laboratory experiments that documented the parasitoid's occurrence, abundance, behaviour, and developmental cycle.

The field surveys were conducted at study sites located across Kansas and Colorado. The surveys found that a bit over a quarter of male cicadas were infected with E. erro larvae, and because of how the flies track down their host, almost all the infected cicadas were male - except for one very unlucky female cicada, which most probably got infected because she was responding to the call of a male, ran into a larvae-ladened E. erro that had the same idea, the latter decided that any cicada will do. Talk about a case of fatal attraction!

And it is indeed the sound of the male cicada's serenade that draws in those flies - a loudspeaker playing the recordings of cicada calls is sufficient to attract the attention of E. erro, but a female fly need more than that to commit to dropping off her precious offspring. In outdoor cage experiments where flies and cicadas were housed together and allowed to mingle freely, the researcher observed that even if an E. erro finds herself perched next to a cicada, she will only attack when the host makes any sudden movements. So E. erro uses two separate signals to track down its prey; an acoustic signal at long range in the form of the cicada's call to guide them in, and a visual signal at close range in the form of cicada movement to confirm the host's identity

Emblemasoma erro larva emerging from a cicada
From Figure 6 of this paper
Once she has confirmed her target, the female fly makes an attack run, and very quickly drops off between 1-6 maggots (usually 3) on the base of the cicada's wings. As soon as the maggots land, they immediately start burrowing between the segments and into the cicada's body. The maggots then start devouring its host alive from the inside. Depending on the temperature and clutch size, they take about 88 hours to reach a large enough size to start pupating. At the end of this period, the maggots use teeth-like "oral hooks" to chew their way to freedom, fall onto the soil below to become pupae, and leaving the cicada an empty husk.

So while the aim of the male cicada's singing is to attract the attention of female cicadas, some of them may instead end up getting attention from females of a very different species, and become reluctant incubators for the broods of some keen-eared, cicada-hunting flies.

Reference:
Stucky, B. J. (2015). Infection behavior, life history, and host parasitism rates of Emblemasoma erro (Diptera: Sarcophagidae), an acoustically hunting parasitoid of the cicada Tibicen dorsatus (Hemiptera: Cicadidae). Zoological Studies, 54: 30.

March 11, 2015

Crassicauda magna

During this blog's first year back in 2010, we featured a parasitic nematode (roundworm) that lives in the placenta of sperm whales of all places. Today, we're featuring a study on another nematode which lives in the sperm whale's cousin - the much smaller and more enigmatic pygmy sperm whale Kogia breviceps.
Photo of C. magna in whale tissue from Fig. 1 of the paper

Crassicauda magna is a parasites that really gets under the skin of the pygmy sperm whale. While most worms in the Crassicauda genus live in the urogential and renal system of whales, C. magna just had to be different from the rest of the pack. Instead of living in the whale's plumbing system, it had opt for a life being sandwiched between layers of blubber and muscle, living snugly under the whale's subcutaneous tissue.

While it can be a tight fit in there, C. magna can grow quite large -the largest known fragment is 3.7 m (about 12 feet) long, but due to where they are found in the body and the relatively cryptic nature of its host, no fully intact C. magna has ever been retrieved. The original species description for C. magna was published in 1939, and was based upon fragmentary remains from the front half of the worm, as the rest of the parasite not recovered.

Even though this parasite appears to have a global distribution (like its host), very little is actually known about it. Only a few anatomical details have been recorded, pieced together from worm fragments which had been collected over the years, and until the publication of the present study, there were no genetic data for C. magna. This is not too surprising considering that much of what is known about the pygmy sperm whale itself (let alone C. magna) had about from examining stranded individuals - which is not exactly a routine occurrence.

The C. magna specimens which were the subject of this new study were retrieved from a dead pygmy sperm whale which was beached at Moreton Bay, Queensland. Most importantly, from a taxonomist's perspective, the research team involved was able to retrieve parts of the tail from male worms. The reason why this was kind of a big deal is that one of the key features used to identify different species of nematodes are the needle-like structures on the male genitalia call copulatory spicules. The male worms use these spicules to pry apart the female worm's vulva for sperm transfer, and it just so happened that each species have distinctively shaped spicules, which can be used to tell them apart.

The researchers were able to compare the worms collected for this study with other specimens of Crassicauda stored at the South Australian Museum, the Natural History Museum in London, and the Muséum national d'Histoire naturelle in Paris. They noted that the spicules on C. magna are remarkable similar to those found on another species that was described in 1966 call Crassicauda duguyi - which was also collected from the neck muscle of a pygmy sperm whale (in this case, it was stranded on the west coast of France). Their conclusion was the C. duguyi is most likely just C. magna instead of being a different species, but the taxonomist who described it was not able make the match because the original species description of C. magna did not have information on the male genitalia.

Unlike previous studies, the researchers responsible for the current one also managed to extract some genetic material from the worms they collected. They sequence a section of the worm's ribosomal DNA which was used to reassess the classification of C. magna in relation to other parasitic nematodes. With such a genetic marker at hand, it can be used in the future to find out more about this enigmatic parasite and its equally cryptic host.

Reference:
Jabbar, A., Beveridge, I., & Bryant, M. S. (2015). Morphological and molecular observations on the status of Crassicauda magna, a parasite of the subcutaneous tissues of the pygmy sperm whale, with a re-evaluation of the systematic relationships of the genus Crassicauda. Parasitology Research 114: 835-841

February 24, 2015

Gelis agilis

It's a bug-eat-bug world out there and the same applies to parasitic wasps - even parasites can themselves become parasitised - which is why some parasitoids recruit their dying host as defence. The parasitoids that go after other parasitoids are call "hyperparasitoids" and the species we are featuring today is Gelis agilis, a tiny wingless wasp that lays its eggs in the cocoons of parasitic wasps such as Cotesia glomerata.
Photo of Gelis agilis by Christophe Quintin

This hyperparasitoid wasp has more to contend with than just overcoming their host's reluctant bodyguard. It is after all a small insect which equates to a handy mouthful for many potential predators. The adult G. agilis is a tiny (3-5 mm) and seemingly defenceless - it doesn't even have wings to fly away from any danger. But G. agilis makes up for that with a clever masquerade

If there is a group of tiny insect which are generally regarded as pretty unpalatable, it is ants (except for animals that specialise on eating ants), so many other creatures have evolved to mimic them in one way or the other. When it comes to playing the part of an ant, G. agilis is a method actor - not only does it look and act like an ant, it even smells the part. When agitated, it emits a volatile chemical call sulcatone, which is the same chemical used by ants as alarm pheromone to rally colony members to their defence.

This "full spectrum mimicry" pays off. Spiders that normally pounce straight onto similarly-sized insects such as fruit flies or parasitic wasps like C. glomerata would hesitate or back right off when confronted with Gelis. A species related to G. agilis - G. aerator - looks and acts like an ant but lacks the distinctive "antsy" smell. When G. aerator was put through experimental trials up against hungry wolf spiders, most spiders back off due to its ant-like appearance. But the lack of matching ant BO was enough for a few more daring (or desperate) spiders to get the jump on G. aerator.

By playing the part to its fullest capacity - behaviour, appearance, and scent - G. agilis is better able to evade its predators to survive another day, and go on to make life a living hell for other body-snatchers

Reference:
Malcicka, M., Bezemer, T. M., Visser, B., Bloemberg, M., Snart, C. J., Hardy, I. C., & Harvey, J. A. (2015). Multi-trait mimicry of ants by a parasitoid wasp. Scientific Reports 5: 8043

February 12, 2015

Trichomonas gypaetinii

What does the cause of pigeon canker, today's parasite, and the most common curable sexually transmitted infection in the world have in common? All of them are parasites from the genus Trichomonas. The species that causes pigeon canker is T. gallinae, a protozoan that lives in the upper gastrointestinal tract of pigeons, and it is currently posing a significant threat California's only native pigeon. While T. gallinae does not always cause disease, when the host is stressed, the parasite multiplies, causing lesions to develop in the throat and mouth of their host. The host eventually dies from starvation as the lesions makes it difficult for them to swallow anything. It is possible that a parasite like T. gallinae might have even brought down the occasional Tyrannosaurus rex over 65 million years ago - though the culprit is most likely to have been a different (but similar) species of parasite given how long ago that it all happened.
Photo composed from Fig. 5 & 6 of the paper

With T. rex being one of the most badass dinosaur of all time, it is appropriate that the species of Trichomonas that we are featuring today - T. gypaetinii - is found in some pretty badass living dinosaurs as well. This parasite was first isolated from a bearded vulture (Gypaetus barbatus) - which I am sure most would agree  is a very handsome and intimidating bird. When T. gypaetini was initially isolated, it was not fully described as a species, as there was insufficient material  to do so. However, this study reports on newer samples obtained from a wide epidemiological study of avian trichomonosis in Spain. The research team managed to obtain isolates of T. gypaetini from another two species of vultures - the Egyptian Vulture (Neophron percnopterus) and the Black Vulture (Aegypius monachus) - and now we have a formal description.

So what differentiates T. gypaetinii from canker-causing T. gallinae? There was nothing about their appearance which separates the two species, but when the research team did some genetic analysis on the parasite, they found that all the Trichomonas samples from vultures were perching on their own branch, far away from T. gallinae. When they search for previously published sequences of Trichomonas from vultures, they hit upon the previously undescribed isolate from the bearded vulture mentioned earlier.

So where does T. gypaetinii sit on the Trichomonas family tree? Genetically, T. gypaetinii is actually more similar to T. vaginalis - a sexually transmitted parasite that infects over 160 million people worldwide each year - most of the time without them being aware of it as most cases show no symptoms. Much like those cases of T. vaginalis infection, T. gypaetinii does not appear to cause any problems to their bird host either.

Furthermore, it seems that T. gypaetini is only found in carrion-feeding birds. Other birds of prey can get infected by T. galinae - the canker-causing species - through eating other birds, especially pigeons. But the vultures' comparatively specialised diet and digestion physiology (especially that of the bone-munching bearded vulture) means that  T. gypaetinii is the only Trichomonas that can successfully make vultures their hosts.

Reference:
Martínez-Díaz, R. A., Ponce-Gordo, F., Rodríguez-Arce, I., del Martínez-Herrero, M. C., González, F. G., Molina-López, R. Á., & Gómez-Muñoz, M. T. (2015). Trichomonas gypaetinii n. sp., a new trichomonad from the upper gastrointestinal tract of scavenging birds of prey. Parasitology Research 114: 101-112.