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Pond water ‘microforay’: amoeba and ciliate sex gone horribly wrong

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Am back, I hope! Don’t pay any attention to the dust… “What dust?” Exactly.

It took a while, but after finally attaining the necessary potentially-overpriced fancy pieces of glass, the lab scope can now take acceptable DIC images. Meaning yours truly can once again slightly misappropriate lab resources during strange hours of the night and stare at protists ‘from the wild’. I return with a bucket of images to gradually unload upon y’all, a couple at a time. Hopefully this’ll gradually massage this dessicated writing brain into eventually oozing out more informative posts. Oh, and if anyone asks — science is hard. Just thought I’d share that.

First off, because we love squishy things, an amoeba. Not sure which one this is (those bastards are notoriously full of attitude when it comes to identifying them by shape… possibly because their shapes are so dynamic, and our brains just suck at processing that), but in the left frame you can see little nubby protrusions sticking out of the flattened pseudopodium. These disappeared after some time. I’m not sure what exactly prompted this amoeba to have goosebumps (podbumps?) on its pseudopod, but some well-prepared SEMs (electron micrographs, in 3D) show that even the classical Amoeba proteus isn’t as smooth and gooey as it looks — the critter is lined with tiny microvilli, much like your intestine. I must add here that there is still much to learn about motility in free-living amoebae — while much of the classical cell biology has been done in Amoebozoan amoebae, the modern molecular cell biology largely focuses on animal cell cultures, which are quite derived, and very much not self-sufficient. The image on the right shows another optical section through the same amoeba. The prominent round thing in the middle, with a bulge inside, is its nucleus — you can almost make out the unusually thick envelope, and the bulge in the middle should be a wad of densely packed chromatin constituting the nucleolus. I wonder what the speck in the middle of that is… One could also make out some food vesicles, as well as a half-digested diatom. I suspect the very clear bottom-most vesicle is the contractile vacuole, which acts much like our kidneys do in regulating osmotic pressure within the cell (so it doesn’t explode).

(click the images to enlarge)

Our next critter is a member of one of my favourite groups of ciliates: the spirotrichs. Spirotrichs are awesome: not only do they have cilia bundled up into adorable little “feet” (cirri) — with which they quite literally walk along surfaces — their nuclei (yes, plural) are weird. Even by ciliate standards. The ‘boring’ ciliate way of doing nuclei involves carrying two types of them: a small one that gets carried around and transmitted through generations, but not transcribed; and a large one that is transcribed, but destroyed and created anew each time it mates. There’s a whole clusterfuck of epigenetics between the small germline nucleus and the new large somatic nucleus that is created from it, and in spirotrichs it has led to chunks of the genome being scrambled in the germline nucleus. Before the somatic nucleus can use it properly, the segments of the genome have to be cut up and placed in the right order so the genes are legible. There’s more on gene scrambling in this post on Aspidisca, another spirotrich (of a subgroup that doesn’t do that, but I needed an excuse to ramble about it there at the time). Also, did I mention spirotrichs are just plain CUTE? (the bottom centre frame has two granular somatic nuclei visible in the middle; to the right of the top somatic nucleus in the bottom right image lies a relatively large germline nucleus; in most other ciliate groups this nucleus is much harder to see)

Speaking of Aspidisca, here are a couple of them hanging out with some random flagellates (prominent one with long plates on it is a euglenid):

As far as protists go, ciliates like to have lots of sex, or else their somatic nucleus decays without replacement (some ciliates can, ummm, deal with mate shortages on their own — but those are rare, though quite convenient in the lab). However, as one might expect, sometimes sex can go horribly, horribly wrong. This pair of spirotrichs has gone too far and fused their entire front ends (where the mouth ciliature is, right of image) — unfortunately, this adventure has proven to be a lethal one. The nuclei here are fragmented for meiosis and are difficult to resolve, although I do think I see some fragments between the end of the ‘mouth’ (thing with lines across it — those are special oral cilia) and the contractile vacuole just below the fusion of the two tails. I should probably consider labeling these next time…

And lastly, something a bit more familiar, by being a fellow animal: a rotifer. At its front end to the right are the cilia which it uses to form water currents (and fool some students, schoolteachers…and zoologists (in the 19th century anyway) into thinking it’s a ciliate); just below those are the jaws that are hard to see — look for the structure with a line running down the middle, where the two of them meet. Then there’s a bunch of big multicellular organs I know nothing about, and towards the posterior end, just above the toes, is what someone pointed out to be an ovary. Unfortunately, that’s the extent of my rotifer knowledge, although I do know this one is not one of the permanently asexual Bdelloid rotifers.

That’s it for this round, but there will be plenty more to come! And maybe even a real post in a little while.

Psi Wavefunction About the Author: Psi Wavefunction is a graduate student working with protists (the 'other' eukaryotes) at Dalhousie University in Halifax, Nova Scotia, and now blogs about protists and evolution at Skeptic Wonder. Follow on Twitter @Ocelloid.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Christopher Taylor 4:43 am 04/18/2012

    The really cool thing that I know about spirotrichs is that some of them are incredible eaters. Apparently Euplotes is able to generate the equivalent of twice its cell surface area in vacuole membrane when feeding (excuse self-promotion). As far as I can work out, that’s roughly comparable to a human being able to swallow a Robin Reliant.

    Link to this

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