"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

May 8, 2014

Nematocenator marisprofundi

Parasitism is the most common mode of life on Earth and it can found everywhere, in all kinds of environments. Even in extreme places such deep sea hydrothermal vents, amidst hellish geysers pouring out hot sulfide or seeping methane, parasitism carries on as usual - the players may change, but the game stays the same. While on this blog most of the nematodes we have featured are the parasites, in this particular case, they play the role of the host.

SEM photo of D. marci from the paper
Laying about 85 kilometres off the coast of Oregon, under about half a mile (800 metres) of water is the Hydrate Ridge methane seeps. These vents are covered in mats of sulfide oxidizing bacteria which are crawling with worms - mostly nematodes from the genus Desmodora. One of these species happens to be a host to the parasite we are featuring today - Nematocenator marsiprofundi - which translates into "nematode eater of the deep sea". It is a microsporidian - a group of single-cell parasite somewhat related to fungi, and taxonomically speaking, N. marsiprofundi lies right near the base of the split between these two groups.

Microsporidians are found in a wide range of animals including vertebrates such as fish and reptiles, as well as invertebrates such as insect, crustaceans, and nematode worms. The host of N. marsiprofundi, a nematode named Desmodora marci (see above), is one of the more abundant animal at methane seeps. There can be as many as twenty worms for each millilitre of carbonate rocks from such locales, and over half of those worms would be infected with N. marsiprofundi. This parasite seems to be common at such vents and were found at sites which are 15 kilometres, so N. marsiprofundi is not localised to just a particular location and/or worm population.

Spores of N. marisprofundi
(image from the paper)
The spores of this parasite (see left) are mostly found in the worm's reproductive tract; in female worms, the spores sit in the uterus next to the eggs, and in the male, the spores lined the worm's sperm duct and cloaca. This led the researchers who found this parasite to suggest that N. marisprofundi is sexually transmitted between its host. However, they also noticed some stages of the parasite were situated in the body wall, where they seem to degrade and digest the worm's muscle tissue, not unlike the microsporidian we featured a two months ago which infects an amphipod that has become invasive in Central Europe.

While their presence in the body wall and the effects they have on their host's muscle indicates they can be quite harmful and may transmit through means other than the worms' sexual activities, that is not to say that this parasite might not exploit multiple mode of transmission. Some parasite change their shape and infect different host tissue at different stages of their lives, and it is possible that N. marisprofundi can both be sexually transmitted and also eventually kill their host to allow their spores to disperse from a rotting cadaver

Studies like this shows parasites might be more common in the deep sea that we might have previously suspected, and that even in seemingly extreme environments like hydrothermal vents, there is good living to had as a parasite. Parasitism is everywhere on this planet, and while many people may think parasites are odd freaks of nature, in reality they are just a normal part of life on Earth.

Sapir, A., Dillman, A. R., Connon, S. A., Grupe, B. M., Ingels, J., Mundo-Ocampo, M., Levin, L. A., Baldwin, J. G., Orphan, V. J. & Sternberg, P. W. (2014). Microsporidia-nematode associations in methane seeps reveal basal fungal parasitism in the deep sea. Frontiers in Microbiology 5: 43.

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