Arthurhumesia canadiensis

Parasites come in all kinds of bizarre shapes and you don't get much more bizarre than today's parasite - Arthurhumesia canadiensis. This species is a parasitic copepod that lives inside the intestine of the compound ascidian (sea squirt) Aplidium solidum. The diagram shows a female specimen, with a pair of lobe-like egg sacs attached. And if you are wondering "what's the weird little blob the arrow is pointing at?", well that's the male copepod. This weird little crustacean is named after Arthur Humes - a very prolific taxonomist. Over the course of 60 years, he was responsible for describing over 700 new species of parasitic copepods. So it's only right that a copepod named after him would appear on a blog which is about parasite biodiversity!

Reference:
Bresciani, J. and López-González, P.J. 2001. Arthurhumesia canadiensis, new genus and species of a highly transformed parasitic copepod (Crustacea) associated with an ascidian from British Columbia. Journal of Crustacean Biology 21(1): 90-95.

Contributed by Tommy Leung.

Alaria marcianae

This horned little devil is the mesocercaria of the trematode, Alaria marcianae, which has a very unusual life cycle. When the metacercariae of this species are ingested by a lactating carnivore such as a Florida panther, they migrate to the tissues instead of developing in their normal site, the small intestine, and develop to this stage. They can then be passed in the milk to the kittens, where they develop normally in the intestine to the adult stage. Females can continue to transmit mesocercariae to future litters until exhausted of their infections.

Contributed by Mike Kinsella.

After One Year, Just the Tip of the Iceberg

Throughout this year we've met blood-feeders, mind-benders, parasitic castrators, brood usurpers, outrageous shape-shifters, skin-clingers, eye-invaders and deadly plagues, but this is only a minuscule fraction of the true biodiversity of parasites. For some perspective let's calculate the number of years it would take to feature all the known metazoan parasites (such as worms, lice, and other multicellular animals) at a rate of one per day:

Myxozoa >1350 = 3.70
Trematoda >18000 = 49.30
Monogenea >20000 = 54.95
Cestoidea >5000 = 13.67
Acanthocephala >1200 = 3.29
Nematoda >10500 = 28.77
Mollusca >5600 = 15.34
Arachnida >30800 = 84.38
Crustacea >5360 = 14.68
Insecta >9400 = 25.75

Even without the odds and ends with less speciose groups like the Nematomorpha and Pentastomida, it would take us a little over 295 years just to feature every known and described species of metazoan parasites. This number does not include the multitude of undescribed species out there; a recent study (Randhawa and Poulin 2010) estimate that 3600 species of tapeworms are yet to be described from elasmobranchs (sharks and rays) alone - so that's another 10 years worth of tapeworms, all undescribed. The number of species of monogenean yet to be described is greater still, with 21000 - 22000 species yet to be described (Whittington 1998) - that's more than another 57 years' worth. For the digeneans, parasitic flukes, in Australia alone, over 5500 species are yet to be described (Cribb 1998) - 15 years worth of worms. All undescribed and unknown to science.

And that is just from the flatworms, which form one phylum out of many. What about the arthropods? And the nematodes? There is no reasons to think why there would be any fewer undescribed parasitic arthropods and nematodes than there are undescribed parasitic flatworms, and if such trend holds, it is likely that it would take an entire millennium to feature all described and undescribed species of metazoan parasites.

But that in itself is merely the tip of a very, very large iceberg. Moving away from the animals, what about the many parasitic fungi and plants? Parasitism as a life-style is just as common in fungi and plants as they are in animals. What about the eukaryotic single-cell parasites? This include the apicomplexans and the trypanosomes, which include parasites which cause diseases like malaria and sleeping sickness.

On top of that, throughout the year, we also featured many pathogenic bacteria and virus, and their diversity readily dwarfs the diversity found in the eukaryotes. With the use of new technology such as metagenomics, we have only begun to scratch the surface of their mind-boggling diversity. For this blog, we have looked beyond the traditional definition of a "parasite" to also included phytophagous insects (which technically are merely insects that are parasitic on plants rather than animals), and animals which have some aspect of "parasitism" to their life-style, such as brood parasites and kleptoparasites.

The Year 2010 was named as the "International Year of Biodiversity" and this blog was our attempt at showing the amazing, cool, and sometimes gross diversity just in parasitic organisms. But, we have barely scratched the tip of the iceberg with this blog and if this iceberg represents all the species which have been described, then it is merely a small chunk from a much greater ice sheet. Any study of biodiversity that does not take parasites into account will be ignoring the elephant in the room...or should I say the lively colony of critters living in and on the elephant?

We hope that you have enjoyed your daily dose of parasites throughout 2010. We'll continue to add other posts on cool and new and interesting parasites, so please follow the blog if you want to be alerted when these are added.

Finally, a big thank you to the more than two dozen people who contributed over the year and a HUGE thank you to all of you for reading this, sharing this, and giving us your comments and questions.

References:

Cribb, T. H. 1998. The diversity of the Digenea of Australian animals. International Journal for Parasitology 28: 899-911.
Randhawa, H.S. and Poulin, R. 2010. Determinants of tapeworm species richness in elasmobranch fishes: untangling environmental and phylogenetic influences. Ecography 33: 866-877.

Whittington, I.D. 1998. Diversity "down under": monogeneans in the Antipodes (Australia) wih a prediction of monogenean biodiversity worldwide. International Journal for Parasitology 28: 1481-1493.

-- By Tommy Leung and Susan Perkins

December 31 - Guignardia bidwellii

As you raise your glass of champagne tonight and toast this wonderful year of biodiversity, don't forget the parasites. And, to help you remember, today's parasite is after the grapes cultivated for wine. Guignardia bidwellii is a species of ascomycetous fungus that causes a disease called "Black rot" in many varieties of grapes in North America and now Europe, South America, and Asia as well. The vectors of this disease are not mosquitoes nor plant bugs, but rather raindrops, which splash the infective spores onto uninfected plants. Infection of the fruits will cause the grapes to shrivel up into what are known in the industry as "mummies" and these can serve as a good place for the fungus to overwinter.

December 30 - Bunocotyle progenetica

Bunocotyle progenetica is another parasite (see also Parvatrema margaritense) that has been thoroughly studied in the White Sea. Being a hemiurid trematode, it possesses all the typical life cycle stages. But when it comes to hosts, we see something entirely different. Hydrobia snails serve as an “all-in-one” habitat throughout the parasite's life. That is, cercariae don't leave the rediae but instead continue their development, up to an adult stage, still inside the same mollusc. The photo shows a redia with adults inside, with visible eggs inside them. The eggs are transferred to neighboring Hydrobia molluscs after the host's death. This favours increased snail exploitation by B. progenetica, since it doesn't require the host to live long. Thus the entire life of B. progenetica passes inside its host, with no free-living stage at all. This phenomemon is not uncommon among parasites as it provides maximum protection against a potentially hostile environment. The serious drawback of such a strategy, though, is lack of dispersal opportunities. It's possible to overcome this by using mobile hosts, however, not the case here, thus B. progenetica is a good example of just how odd parasites can sometimes be.

The PhD thesis referenced is entirely dedicated to this parasite, while the second paper only has certain comments on it.
Levakin I.A. Realization of a one-host life cycle of Bunocotyle progenetica (Trematoda: Hemiuroidea: Bunocotylinae) at the White Sea intertidal zone. PhD thesis manuscript, 2007. (In Russian)

Gorbushin, AM, 1997: Field evidence of trematode-induced gigantism in Hydrobia spp. (Gastropoda: Prosobranchia). J. Mar. Biol. Ass. UK 77 , 785–800.

Contributed by Anya Gonchar, photo by Ivan Levakin.

December 29 - Eremitilla mexicana

Back in 1985, Wayt Thomas, a scientist from the New York Botanical Garden discovered an unusual plant in Mexico. It had a little bloom of dense flowers that kind of looked like a pinecone and nothing else but a thick stalk - no leaves or chlorophyll anywhere. It was so unusual that Thomas did not know what it was and could only speculate as to even what family it might be in. The strange plant eventually made its way to George Yatskievych at the Missouri Botanical Garden and twenty years after it was first discovered, he traveled back to Mexico in search of more. He went to the same location - and even employed the very same guide that Thomas had - and finally, after several days of hunting through stream beds in the Sierra Madre del Sur, they found a small population and took a few samples and many photographs. They did not collect very many because it is believed to only occur in this one small region - it has never been observed elsewhere. A second trip allowed Yatskievych to identify the host plants as Hedyosmum mexicanum and it has now been named Eremitilla mexicana, which means "little Mexican hermit."

Photo by George Yatskievych.

December 28 - Hyalomma dromedarii

The three wise men are said to have brought three gifts, but perhaps they brought four. The tick, Hyalomma dromedarii, is the most common ectoparasite of camels found in the Middle East. Because of the high temperatures, the females need to burrow down into the sand to lay their eggs. The larvae find a host and feed, but unlike ticks in more temperate climates that usually then drop off to molt, the larvae of H. dromedarii stay put on their host, molt, and feed again. The first host may be a rabbit, hedgehog, bird, or other small livestock, however if the first host that they feed from is a camel itself, they will sometimes stay right there and complete their entire life cycle on the same host. Dropping off into the hot sand is just far too risky, it seems.

Image is from this site.

December 27 - Macrophomina phaseolina

One of the gifts that the Three Wise Men brought was frankincense, which is derived from the resin of the tree Boswellia serrata. While frankincense has been considered as a remedy for many different types of infectious diseases, B. serrata itself is by no means free from the scourge of infection itself and is plagued by the fungus Macrophomina phaseolina, which causes the disease known as Charcoal Root Rot. This fungus infects more than 300 species of plants, and can cause high mortality among tree seedlings. Macrophomina phaseolina survives and overwinters as small, black spores (call microsclerotia), hidden in the soil or debris from previously infected plants. When a growing root of a plant encounters a dormant spore, it germinates and begins growing all over the root and penetrating into the root cortex. From there, the fungus penetrates through the cortex and inner bark and into the taproot. The infected seedling eventually dies from the gradual destruction of its root system. Just prior to the death of the host, the M. phaseolina produces spores that are deposited in the inner bark of the lower stem and roots. When the host eventually dies and decays, the spores are released into the soil where they wait for an encounter with yet another growing seedling.

Contributed by Tommy Leung.

December 26 - Plasmodium vivax

In Christian lore, three wise men, the magi, traveled from the East bearing gifts for the baby Jesus. These gifts were gold, myrrh and frankincense, a resin made from trees in the genus Boswellia. The reason for the gold seems obvious, myrrh was used as an incense, which had to have made the stable smell better, and frankincense was used for many things, several related to improving ones health, including ingesting the resin to combat arthritis and other ailments. Frankincense was also burned to ward off mosquitoes and thus the diseases that they carry. One of the most important mosquito-borne diseases at that point in time in that region was malaria, in this case caused by the parasite, Plasmodium vivax. Unlike it's cousin, Plasmodium falciparum, which kills many of the people it infects, P. vivax produces a milder form of the disease, though still with the classic symptoms of profound fever and chills. P. vivax has cycles every 48 hours and is sometimes thus known as "tertian malaria." (See the entry for Plasmodium malariae if that's confusing to you.) This species has a very widespread distribution and, in fact, used to cause early Americans as far north as Philadelphia and New York City to get sick every summer. Though it may kill fewer people, this parasite maintains stages in the liver of its host and can cause relapses of the disease for decades after the initial infection.

December 25 - Trypanosoma lewisi

On December 25, 1643, Captain William Mynors and his crew aboard the ship the Royal Mary, sailed past a small island in the Malaysian archipelago and dubbed it "Christmas Island." More than 300 kilometers away from the nearest other piece of dry land and uninhabitated by humans or their animals until the 1890's, many of the animals and plants found here were unique to this island. These species included two endemic species of rats, Rattus macleari and Rattus nativitatis. Despite the fact that the first settlers found them to be abundant, within a very short time, i.e. by 1908, the two species had gone extinct. Why? In the early 1900's, a tropical parasitologist had noticed several Rattus macleari individuals acting sickly and he speculated that they had been infected with trypanosomes. This was nothing but a hunch for almost exactly a century at which point molecular diagnostic techniques were brought into the picture. Scientists, including some of my colleagues at the American Museum of Natural History, took rats that had been collected from Christmas Island and deposited as specimens into natural history museums, extracted DNA from them and tested them for trypanosomes. Sure enough, many of the rats collected after humans arrived on the island showed evidence for infection with the parasite, Trypanosoma lewisi. The scientists also tested three rats collected prior to any settlements and none of those tested positive. Thus, it appears that fleas bearing T. lewisi hopped off the black rats (Rattus rattus) on the ship, bit the island's endemic rats and transmitted the parasite. The naïve hosts were likely killed by these parasites and went extinct.

You can read the whole paper here. Image is from this site.