A Whiff of Tax­on­omy – Lacry­maria olor

by Roberto

I was re­cently made aware of one of Earth's "most in­ter­est­ing liv­ing be­ings ow­ing pri­mar­ily to its power of elon­ga­tion, its won­der­ful elas­tic­ity and its great free­dom of move­ment."  Thus be­gins a cap­ti­vat­ing 1911 ar­ti­cle by S. O. Mast, de­scrib­ing the amaz­ing fea­tures of the cil­i­ate Lacry­maria olor. Its name al­ready hints at its shape: a cell body in the form of a tear (Latin lacryma) out of which pro­trudes a long pro­boscis rem­i­nis­cent of a swan's neck (Latin olor).

Fig.1. Lacry­maria olor cel­lu­lar fea­tures. Top: the long "neck" of L. olor. Source Mid­dle: the dis­tinct cell mor­pholo­gies be­tween ac­tive con­tracted and ac­tive elon­gated states in live cells im­aged us­ing dif­fer­en­tial in­ter­fer­ence con­trast (DIC) mi­croscopy. Scale bar, 40 μm. Source Bot­tom: con­fo­cal flu­o­res­cence z‑stack pro­jec­tion of an α‑tubulin–stained fixed cell re­veals the he­li­cally arranged cor­ti­cal cy­toskele­ton. Source.

It is dif­fi­cult to know ex­actly when L. olor got its name; I found a source point­ing back to the Dan­ish nat­u­ral­ist O.F. Müller. If you are cu­ri­ous and can read Latin, you might want to browse his 1876 trea­tise on flu­vial and ma­rine pro­tists (in­fu­so­ria). I'll ad­mit, I was not up to the task. In any case, nat­u­ral­ists have gazed (through mi­cro­scopes) at L. olor in won­der­ment for cen­turies.

What makes L. olor so ut­terly spe­cial and cap­ti­vat­ing? Just look at the thing! In its search for food, it can stretch its pro­boscis to many times the length of its cell body. Amaz­ingly, this re­versible stretch­ing can go from com­pletely with­drawn to longer than thirty body lengths in thirty sec­onds. You get a sense of the speed of the process from the two mid­dle pan­els in the fig­ure: all that stretch­ing in the span of a sec­ond! In ad­di­tion, you get a sense of the dy­nam­ics of the cel­lu­lar processes un­der­ly­ing the "neck stretches" from the dra­matic changes in the cy­toskele­ton re­vealed in the bot­tom panel of the fig­ure. Of course, the ideal way to vi­su­al­ize L. olor is in "real time." So, have a look at this video.

Fig. 2. Mem­brane-mi­cro­tubule un­spool­ing, curved crease origami in a liv­ing cell. A: schematic of the mem­brane pleats along the cell dur­ing ex­ten­sion. 1 to 3: zoom-ins of the mem­brane and cor­ti­cal cy­toskele­ton folds in the body, tran­si­tion zone, and neck (re­spec­tively) of an elon­gated cell. B: folded origami struc­tures (Lacrygami) are pulled to elon­gate, demon­strat­ing d‑cone sin­gu­lar­ity prop­a­ga­tion through se­quen­tial open­ing of the curved crease pleats. Scale bars, 25 mm. Source

How does L. olor ac­com­plish this be­hav­ior? A re­cent pa­per by El­liot Flaum and Manu Prakash from Stan­ford Uni­ver­sity re­veals the un­der­ly­ing mech­a­nism. The en­tire po­ten­tial length of the neck is stored, folded in he­li­cal lay­ers of mem­brane and cy­toskele­ton. The au­thors re­fer to this geom­e­try as a "curved crease origami" or "Lacrygami." As the forces gen­er­ated by the beat­ing cilia along the neck and around the mouth pull, the Lacrygami quickly and eas­ily un­folds (Fig. 2A). Re­al­iz­ing that geom­e­try is scale-free, the au­thors tested the fea­tures of this mech­a­nism in a scaled-up model of pa­per origami (Fig. 2B). It took me a bit of time, but I fi­nally was able to fold a piece of pa­per. It was cer­tainly thrilling to get a sense of how quickly and eas­ily it is to un­fold and re­fold the pleats. If you have some time to spare af­ter read­ing the pa­per, I en­cour­age you to try it. The so­lu­tions of evo­lu­tion will never cease to amaze me!

 

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