My previous two Sunday Protist attempts got derailed. With the first one, noticed there was quite a bit to say about them, and decided to postpone it for later as it was a big topic (and unrelated to my current work). Then I picked something relevant to my day job, y'know, two birds one stone, etc. And somehow that led me to paleontology. A warzone in paleontology. Complete and total clusterfuck. With potential inaccuracies here and there that I now need to sort out. Whilst we wait, I'll just do something quick: a case of a foraminiferan apparently growing bacteria and then eating them in perhaps one of the most non-human farming enterprises ever! (leafcutter ants are pretty much human at that phylogenetic distance...)
Textularia blocki lives on seagrass. Many forams have interesting associations with seaweeds, ranging from internal parasitism to epiphytic attachment, usually via secretions of sulfated mucopolysaccharides, a fairly common material in the extracellular matrix. T.blocki, however, is a freely motile foram. It leaves peculiar 'grazing traces' as it crawls along the seagrass, without damaging the tissue beneath it:
Left: T.blocki with grazing traces on blade of seagrass. Right: (Langer & Gehring 1993 J Foram Res)
As made evident in the diagram, the traces consist of two parallel 'walls', consisting of pale whitish adhesive material, presumably containing mucopolysaccharides, devoid of sand grains or other contaminants. Curiously, some forams carried sand grains along, without depositing them. These secretions are formed by pseudopodia, or the 'business' part of the foram: an intricate network of reticulated feet with amazing cytoskeletal properties. When these secretions are left alone in seawater for 48h, a lush garden of bacteria sprung up specifically along the secretion traces:
Bacterial gardens along the foraminiferan secretion traces. Note the relatively clean surface of the leaf outside the secretions, supporting that it is the adhesive mucous that attracts bacterial accumulation (Langer & Gehring 1993 J Foram Res)
When released back into the medium containing the seagrass lined with traces, the forams approach the nearest trace and follow along it, suggesting they use some form of chemical sensing to determine where the secretions are and how they are oriented. The speed is then reduced, suggesting the foram is then busy grazing on their bacterial harvest.
Thus, a 'mere' single celled organism can produce organised tracks of nutritious material, wait for their bacterial crop to grow, and subsequently harvest it. We like to think we invented agriculture. The more biologically-oriented among us point out leafcutter ant fungus gardens and aphid farming. Yet, agriculture has also evolved on the unicellular scale in a small humble foraminiferan living among blades of seagrass. Humbling, isn't it?
Interestingly, a similar behaviour has been described gastropods like slugs and limpets, as their mucous also attracts bacterial growth. Convergence: when a good thing is chanced upon multiple times, it will likely be kept by several lineages independently. This applies to language and cultural evolution as well as that of biological organisms.
We tend to have a deep conviction that cells are dumb blobs of goo, incapable of any sort of behaviour besides basic phototaxis or whatever. We think cells are just simple chemical response machines – which is true. But ultimately, so are we. There is no fundamental distinction between human social dynamics and the adventures of a crawling amoeba. The difference is all in the quantity and complexity of interactions – the higher the complexity, the more random (stochastic) the system appears (and to an extent, is). While I must concede that in terms of the number of components and pathways involved, human or ant behaviours are more complex than that of an amoeba, that does not mean the proverbial amoeba 'lacks' behaviour entirely.
I've mentioned the cellular behaviour stuff before, probably too often for regular readers. Apparently, that idea needs restating though. Also, as a cell biologist, I find it quite...well, pleasing. It's nice that, ultimately, my subjects are no more or less machine-like than humans or plants. Furthermore, where I was heading with this originally, I think part of our notion of cells being 'stupid' comes from the obsession with our own cells. Animal cells are, in fact, quite simple and developmentally retarded. The cause is cell specialisation driven by multicellularity. Eg. an epithelial cell can now afford to lose the ability to hunt around for prey, it no longer needs to coordinate movement in any sophisticated manner, the life cycle can be simplified to terminal differentiation.
Curiously, a similar problem plagues modern science and engineering: overspecialisation means that one must no longer have the same level of foundational education to survive, and thus we end up arguably knowing more about less, or perhaps knowing the same about less. I can suck at math or chemistry and get away with it. In the old days, people had to actually have a broader base just to function. Conversely, there was also less information floating around. Which is more efficient? Just as multicellularity vs. unicellularity, each system has its merits and drawbacks. So it's hard to tell.
A while back I found a paper on cellular complexity in multicellular vs. unicellular organisms that needs to be discussed in greater detail eventually...
ChrisM over at the wonderful Echinoblog (about the cooler deuterostomes; ok, hemichordates and ascidians are cool too) wrote about sperm-eating ciliates infesting starfish.
Lots of things like sperm. For example, Monocystis is a gregarine with a penchant for earthworm sperm – infection rates are so high that if you slice up a worm from your backyard and smear the contents of its seminal vesicles on a slide, the chances are pretty good that you'll find some. And by 'some', I mean, LOTS. So if you're ever in the mood for some apicomplexans, all you need is an earthworm, a blade and a scope. There are parasites in pretty much anything and everything, so if you go around examining various animals, you may well find loads of cool protistan denizens in them. Many of which could be undescribed and, perhaps, new to science.
Langer, M., & Gehring, C. (1993). Bacteria farming; a possible feeding strategy of some smaller motile Foraminifera The Journal of Foraminiferal Research, 23 (1), 40-46 DOI: 10.2113/gsjfr.23.1.40