[it's totally still Sunday in someone's mind somewhere...right?]Reading old protistology books can be quite a frustrating exercise: image you come across a really cool-looking organism, try to follow up on what happened to it since, and discover it's only been written up once in the distant past and neglected ever since. This happens to a very annoying percentage of organisms described in those older books (newer books tend to forget the phantom and near-phantom species). Now this organism in particular at least has a very detailed source behind it, but alas! ...in German. I saw it in Grell's (1973) Protozoology, and the original description comes from... Grell 1950 . The former I have an English copy of, the latter I do not. So don't expect much detail.
Ecologists often lump microorganisms together as 'decomposers' (at least in undergrad courses); those of us living in a different scale of things beg to differ. From an intro ecology text, you get the idea that ecology somehow ceases to happen once you reach a certain size or phylum, and everything's just a part of this amorphous blob that exists to recycle nutrients so that the rest of us can live on. Shockingly enough, this amorphous blob has a whole ecosystem of its own, complete with predators and photosynthesisers and those who do both, as well as parasites and mutualist endosymbionts and saprophytes, etc. They interact with each other in ways not in the slightest less interesting than fluffy animals. In the microscopic world, cells become bodies that, just like ours, can get hunted, infected or benefited by some other organism. Or host a pile of commensals (who do exist, by the way, by similar arguments that Nearly Neutral Theory employs for mutations)
*Zoological ecologists also tend to treat plants as 'those things that exist for animals to eat', which annoys the hell out of anyone dealing with plants. On the first day of ecology the instructor causally mentioned that 'plants don't do much in the way of behaviour', and thus the course will largely ignore them. I expressed disagreement after class, noting there is little fundamentally different between a plant biochemical response leading to, say, discharge of toxins or some regulatory change, and an animal biochemical response leading to observable [to our eye] mechanical change. Yeah, this is why I have difficulty talking to the more 'traditional' biologists sometimes...but that is completely off-topic.
Remember how crabs can sometimes be covered in sea anemonies? Many smaller crustaceans can often be covered in organisms superficially resembling miniature sea anemonies - namely, Suctorians - highly derived (=weird) ciliates covered in miniature tentacles. Suctorians also reproduce by budding, as opposed to conventional symmetrical mitosis employed by the canonical ciliate. Just like sea anemonies and other cnidarians, suctorians also have stalked and swarming forms, like the polyp vs. medusa destinction in the former. Which is quite unsurprising, really, as aquatic sessile organisms usually use specialised free-swimming forms to spread. But still another cool bit of ultimate convergence discussed a couple posts ago.
Top: A copepod covered in suctorians; an SEM of Ephelota gemmipara from the copepod. (Fernandez-Leborans et al. 2005 J Nat Hist) Bottom: Ephelota superba, suctorian episymbiont of Antarctic krill. Quite reminiscent of an anthozoan. (Stankovic et al. 2002 Polar Biol)
Now, imagine a microscopic sea anemone being parasitised by another. I'm not sure whether there are any cnidarian parasites of other cnidarians (wouldn't be too surprised), so the analogy stops around here. The awesome does not, however: parasites are never truly simple. Tachyblaston's infancy consists of finding an Ephelota, attaching itself and piercing the cell membrane to leech off the cytoplasm. Over time, the entire cell can become filled with parasites. During this stage, the parasite buds to produce swarmers.
Afterwards, the swarmers swim around and attach themselves to an Ephelota stalk, where they themselves form a stalked cup structure. There the parasite buds multiple times, yielding a cup full of Tachyblaston, which is subsequently emptied as the buds (this time with a single thick tentacle, according to Martin 1909) evacuate and crawl up the stalk toward the main cell body of Ephelota to infect it and start the cycle over.
Left: Swarmers. The stage that actually sort of looks like a ciliate... Middle: Full 'cup' of Tachyblaston in stalked stage. Right: Empty cup after all (Grell 1950 Z.Protistenk)
To summarise Tachyblaston's life cycle, the cell-penetrating parasites of the Ephelota cell body bud to form swarmers, which, in addition to reminding us of suctorians' ciliate leanings, find another Ephelota and attach themselves to the stalk, forming a cup which they fill up by budding again, finally releasing single-tentacled forms that crawl up the stalk to the next victim. How's that for unicellular organisms having 'primitive' differentiation capabilities?
Tachyblaston's original description by Martin 1909:380 J Cell Sci can be found here. The parasite was very distinctive due to a major refringent particle of unknown origin or function present within each Tachyblaston cell. The genus name reflects the extraordinary speed with which the parasite epidemic can sweep over an entire population of Ephelota, which end up a decimated forest of bare stalks. Creepy.
And last but not least, here's an obligatory tree to orient ourselves phylogenetically:
Tachyblaston and Ephelota are both suctorians in Phyllopharyngea, which contains some other bizarre (and somewhat obscure) creatures like Chonotrichs. (Gong et al. 2008 JEM)
PS: Blogging about ciliates is very difficult. They are too damn distracting - you start reading about one and come across ten others you suddenly must look up, and so on. About as bad as Wikipedia. Actually, since looking these things up is now actually relevant to my day job, the distractions get worse as I feel compelled to write down and follow anything potentially related to work. Just in case. Apparently, sort of using blogger as a reference manager... hence the exploding drafts folder. Sigh.
References:
Fernandez-Leborans, G., Freeman, M., Gabilondo, R., & Sommerville, C. (2005). Marine protozoan epibionts on the copepod Lepeophtheirus salmonis , parasite of the Atlantic salmon Journal of Natural History, 39 (8), 587-596 DOI: 10.1080/00222930400001525
GONG, J., GAO, S., ROBERTS, D., AL-RASHEID, K., & SONG, W. (2008).
n. sp. (Ciliophora, Phyllopharyngea, Cyrtophoria): Morphological Description and Phylogenetic Analyses Based on SSU rRNA and Group I Intron Sequences
Journal of Eukaryotic Microbiology, 55 (6), 492-500 DOI: 10.1111/j.1550-7408.2008.00350.x
Grell, K. (1950). Der Generationswechsel des parasitischen Suktors Tachyblaston ephelotensis Martin Zeitschrift f�r Parasitenkunde, 14 (5) DOI: 10.1007/BF00260027
Martin, CH (1909). Some Observations on Acinetaria: Part I.—The " Tinctin-kbrper " of Acinetaria and the Conjugation of Acineta papillifera. Quarterly journal of microscopical science, 53 (2), 351-389
Having just taken two days off work (one sick day, one leave day), it's currently Sunday in my mind.
ReplyDeleteThis is the first I've heard of it, but Tachyblaston is way cool! BTW, if it leaves a forest of dead stalks behind, then it's a parasitoid and not a parisite, right?
ReplyDeleteAFIAK, most protistan parasites kill off their hosts (eg. by lysing the cell). In fact, I'd argue most cellular-level parasitism is lethal to the cell; in multicellular organisms we don't notice it so much as there's more than enough cells to go around, so in zoology parasitism takes on a separate meaning, requiring a distinction with parasitoid behaviour. I'd argue the parasitoid behaviour is the norm, with non-lethal parasites being kind of a multicellular phenomenon, and thus the non-lethal form should receive a special name, not the other way around. Thus I'll stick with parasite; if people working on small limited clades prefer to attach some sort of different meaning to it, they're more than welcome to do that on their own =P
ReplyDeleteIn protistology, the major distinction is actually predation vs. parasitism, which is quite vague and boils down to whether the attacker is bigger or smaller than the attacked. It gets quite murky... not worth dedicating much attention to, IMO.
Very interesting!
ReplyDeleteI wonder if something similar is going on with the stalked ciliates hitchhiking on the cyclops in a little video I recorded last year:
http://www.youtube.com/watch?v=Dt1Cq-WELw8
I identified them (too casually, I'm sure) as "Epistylis," and forgot about 'em. Your article makes me want to look more closely at these guys.