Field of Science

MM#11 Answer: Rhizochromulina: algal amoeba

ResearchBlogging.orgRemember this from a looooooong time ago?

Rhizochromulina. Mischievously looks like a chlorarachniophyte... [source]

As a warning, about the only marginally comprehensive ochrophyte phylogeny I found was in TC-S & Chao, J Mol Evol. It looks like this, and makes me want to cry:

[no comment needed] (TC-S & Chao 2006 J Mol Evol)

In case those names look simply alien to you, you're not alone. In fact, I wouldn't be surprised if they'd stump some phycologists. Ochrophyte phycologists. This, my friends, is where we enter the bottomless pit of chaos that is Cavalier-Smith Taxonomy. It's a special kind of taxonomy, so I capitalised it.

So Rhizochromulina belongs to Actinochrysia in Alophycidae in Hypogyristea in Marista in Ochrophyta. I wonder if the latter is the only one of those which human beings actually use. Eikrem et al. (2004 Phycologia) put Rhizochromulina and co. in Dictyophyceae, which seems to be the taxon used by the world outside Tom's head. Seems like Dictyophyceae = Actinochrysia exactly; save for a milirank difference. That way, Tom gets to take an old, well-accepted group and liven things up with a fresh name. And get his own attached to it. Damn good deal he's got there...

Anyway back to algal amoebae...Rhizochromulina's fellow Dictyophyceans include the silicoflagellate Dictyocha, a 'heliozoan' Ciliophrys and a loricate flagellate Apedinella[photo]. And Pteridomonas, which appears to be a wannabe Choanoflagellate. Such a small group, such morphological diversity. Although, I don't know whether I can say that yet...

Initially I wanted to do a big overview of Stramenopile (fine, "Heterokont", happy?) amoebae, and take a look at their phylogenetic distribution to try to guess how easy it can be for cells to switch between amoeboid and flagellate forms through their evolution, and whether the easier direction would be from flagellate to amoeba or vice versa. This has some implications in cellular evolution, as well as the overall eukaryotic tree and its much-contested root. TC-S 2009 JEM(free access) argued (sigh.) for an important aspect of the unikont-bikont split being cytoskeletally amoeboid vs. flagellate cell morphologies (see my Naegleria post for further info), as well as evoking lateral transfer of myosin II (a motor protein [mostly] unique to unikonts, that is, opisthokonts like us and amoebozoans(Richards & TC-S 2005 Nature)) to Heteroloboseans (bikonts), enabling their complete transformations between amoebae and flagellates. Ok, take home message: I wanted to have a closer look at the EPIC MESS that is eukaryotic cellular evolution.

I wanted to fix this mess with a group that's well-known, relatively well-studied (or so I thought), with its phylogeny all sorted out. Ooops. Ochrophytes, despite being home for kelps and diatoms and such, do not qualify, apparently -- their phylogeny is a mess, many of their groups completely understudied, and...yeah, my little amoeba exercise kind of failed miserably as I fell deeper and deeper into confusion.

Furthermore, I need to figure out how the various ways of being amoeboid, flagellate, and amoeboflagellate really differ from each other, and how best to classify them to analyse the situation properly. At best, this will take A LOT of reading. But this is overly optimistic -- it assumes that there exists proper reading material in the first place! This story might actually have to wait until we learn more protistan cell biology.

Now that Rhizaria also seems to be among Chromalveolates, things get even weirder. Rhizaria is full of amoebae, full of flagellates, and everything in-between. Although as far as I know, most Rhizarians have at least some flagellate stage, even the Chlorarachniophytes. Rhizaria is also a huge mess, and even more obscure than the Ochrophytes. There's just SO MUCH untapped diversity and opportunity for biologists of all sorts to truly study eukaryotic evolution as it ought to be studied...which is why I get so livid over how cell biology is generally taught -- from this dull, lifeless zoocentric "This gene is linked to cancer" perspective where they seem to think that memorising signal transduction pathways is a worthwhile activity.

No, learning about just how many ways a cell can be is far more worthwhile and educational. It's much more informative to learn biology from a perspective of diversity. I'd argue this is even true for the biomed-oriented spawn of Satan researchers: any kind of biology without comparative work is blind and shortsighted, and to understand how a particular cell type responds in a particular form of cancer, one must first understand how eukaryotic cells work, period. And it's shameful and stupid to foresake the rest of the Eukaryotic Tree when any help is so desperately needed in comprehending the mess that >3 billion years of evolution have left us in.

Enough of my ranting (taking a cell physiol course at the moment, feeling rather sore about the obsession with macrophages and cancer cell signalling)... have another Ochrophyte amoeba:

Some Rhizarians look vaguely like that too. Hmmm.

Yeah, I really hit a brick wall with this post. Don't really have the time to sort out messy fields at the moment, as much fun as it is. Anyway, right, midterm...

CAVALIER-SMITH, T. (2009). Megaphylogeny, Cell Body Plans, Adaptive Zones: Causes and Timing of Eukaryote Basal Radiations Journal of Eukaryotic Microbiology, 56 (1), 26-33 DOI: 10.1111/j.1550-7408.2008.00373.x

Cavalier-Smith, T., & Chao, E. (2006). Phylogeny and Megasystematics of Phagotrophic Heterokonts (Kingdom Chromista) Journal of Molecular Evolution, 62 (4), 388-420 DOI: 10.1007/s00239-004-0353-8

Eikrem, W, Romari, K, Latasa, M, Le Gall, F, & et al (2004). Florenciella parvula gen. et sp. nov.(Dictyochophyceae, Heterokontophyta), a small flagellate isolated from the English Channel Phycologia, 43 (6), 658-668

Hibberd, D. (1971). Observations on the cytology and ultrastructure of Chrysamoeba radians Klebs (Chrysophyceae) European Journal of Phycology, 6 (2), 207-223 DOI: 10.1080/00071617100650231

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