When conditions for life are unfavourable, some protists can cheat death by entering a cryptobiotic state. Usually, they do it by enclosing themselves within thick-walled structures called “resting cysts,” which protect vital genetic material from dehydration and extreme temperatures. Tucked away in their cysts, the cells shut down all metabolic activities and wait for the environment to improve.
My blog has been in cryptobiosis for about eight years. That would would be a cat nap for Acanthamoeba (which can be revived from dormancy after tens of thousands of years), but it’s a big chunk of a human life. A lot has changed in those eight years. The eukaryote family tree has sprouted some new branches, down near the roots. The roots themselves are starting to come into focus, too, thanks to some exciting new work from Dalhousie University.
Meanwhile, up in the higher branches of the tree, molecular phylogenetics continues to shuffle things around. My last post (dated November, 2016!) discussed a novel amoeboid called Lecythium siemensmai. That species is no longer a Lecythium at all, but a member of a genus called Fisculla (named for its resemblance to a bag of money). I should have updated that post seven years ago!
A few things have changed in my life, too. I’m still fascinated by ciliates, but have been spending most of my microscope hours on testate amoebae. This shift in focus was prompted, in part, by some new tools that have been made available to me.
I now have a small perch at the Canadian Museum of Nature, as a Research Associate. The title comes with a keycard that opens doors at the Natural Heritage Campus in Gatineau, where our country keeps its mastodon bones, its bottled molluscs, and its collection of over a million beetles. This magic card also gives me access to some nice microscopes. The most exciting of these, for me, is the museum’s FEI Apreo II Scanning Electron Microscope, which can resolve features that are measured in nanometres (that is, billionths of a metre!).
Here, for example, is a creature I collected in Ottawa’s Mer Bleue bog, a snail-shaped testate amoeba called Lesquereusia spiralis, which assembles its shell from curved siliceous rods (which remind me of Cheez Doodles™):
The tubular “idiosomes” that cover the shell are produced by the amoeba itself, from globules of dissolved silica and proteinaceous “glue”, assembled within the Golgi complex of the cell and secreted from its membranes during the process of shell construction. Zooming in, we see that these idiosomes are held together with an organic cement laid down as a meshwork of tiny rosettes:
Similar meshes are seen in other lobose shelled amoebae (members of the order Arcellinida), but they often differ in appearance. Back in the 1980s, some researchers proposed that different arrangements of organic cement might be used to distinguish taxa within the group, but the idea doesn’t seem to have caught on. The structure of the organic cement is sometimes noted in species descriptions, but I’m not aware of any attempt to use it a taxonomic character for genus or family. Do patterns in the organic cement correspond with lineages of arcellinids, above the level of species? I have no idea, but it seems like a fun thing to wonder about.
