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When you are in the world of microbes, it does not seem necessary to think of the largest land mammal
on earth. What could elephants possibly have to do with a ciliate? When you say this out loud,
any potential connection seems dubious at best. However, if you look at the Dileptus,
you see an elongated, moving body, one that seems like it’s made up entirely of snout—like
an elephant’s trunk, disembodied and shrunk down so that it can survive all on its own.
But unlike the elephant, Dileptus is no gentle giant. It isn’t moving around because it wants
to play or drink water. No,the dileptus is waving around because it is loaded with toxins
and it wants to put them to good use. Now, this may be surprising given its
general blob-like appearance, but the dileptus’ body is divided into two distinct regions:
the proboscis and the trunk, which is confusing because the trunk on the dileptus is not actually
the elephant trunk-like part of the organism. The trunk is, in this case, more like the trunk
of a tree, it’s the base for the rest of the dileptus’ body. The proboscis is the snout, the
part that extends to the rest of the microcosmos and examines it, looking for something to eat.
And interestingly where the proboscis and the trunk connect lies the dileptus’ mouth,
a cavity lined with hair-like cilia that continues down the length of the proboscis. The dileptus can
use these cilia to generate currents in the water that carry food to its oral cavity. You
can imagine it a bit like if your arm hairs could stir up the air around you and levitate the snack
in your hand all the way to your mouth. Which, now that I’m thinking about it, sounds amazing.
But before the cilia can work their magic, the dileptus has to catch its food.
And that’s unfortunate for the Spirostomum at the bottom left corner. It does not know that
on the other side of that piece of debris is a predator that one scientists called “the
king of beasts among the ciliated protozoa” with an appetite that is quote “insatiable.”
The dileptus is not a subtle, lying in wait kind of predator. It’s always moving, always seeking.
And when its proboscis makes contact with the spirostomum,
it grabs a chunk of its body almost instantly. The spirostomum is large and nimble,
and it pulls away quickly as if it’s been stung. But it leaves behind a tasty morsel of itself,
which the DIleptus draws in until it’s close enough to open wide and eat.
And from its safe distance away, the spirostomum may not be whole again yet, but it is at least
out of reach of the dileptus, and of its proboscis, and its hundreds of toxicysts.
You can actually see those toxicysts here, when we look at the proboscis with
1000x magnification. And while the proboscis’ movement through the water may seem like a chaotic
mess of twisting left and right and up and down, there is a surprising order to it all--driven by
the placement of those toxic cellular weapons. The dileptus has to move in a way that lets it
immediately attack its prey upon contact, but its proboscis is only lined with toxicysts
on one side--the side that leads to the oral cavity. So it always sweeps its proboscis
with its toxicysts facing whatever is about to be swept. And when it’s done moving in one direction,
the dileptus rotates its proboscis and sweeps in the other direction.
Again, this is all so that when the dileptus finally hits something, it won’t just make
contact: it will unload needles full of toxins into whatever it has made contact with.
To learn a bit more about how these toxins work, in one experiment, scientists filled a fluid with
the material coming from the Dileptus’ toxins. They then placed some Paramecium into the fluid
to see how they would respond. They did not respond well.
Immediately, the paramecium tried to mount their own defenses by releasing their own harpooning
trichocysts. Now, that might have worked against an actual dileptus, pitting ciliate
against ciliate as they poke each other for survival. But in this experiment, with the toxins
permeating the fluid, the best the paramecium could hope for was to delay the inevitable,
to use its trichocysts as a temporary fence until eventually, it emerged to its own death.
Now, that is an extreme situation, one that a paramecium would probably not actually find
itself in were it anywhere else but in a lab.
Fortunately for paramecium, we do not live in a world full of Dileptus toxin fluid. Those toxins
are kept safely packaged within the organism themselves, waiting for their designated time.
Which does lead us to a final question—one that we do not have an answer for,
but that we like thinking about nonetheless. We’ve seen the dileptus as a solitary organism,
and we’ve also seen it in groups with others of its kind. But how? How does an organism that is so
simple, so reactive, so toxic—how is it able to just casually entwine itself with others
of its own kind? How can they gather without immediately all jabbing each other to death?
Well, we don’t know, but it means that there must be more to the release of toxicysts than just the
simple mechanical stimulus of touch—that there must be some sort of recognition that makes it
possible for two Dileptuses to know each other. You might even call it chemistry.
Now, we don’t know the underlying signs and signals that make that recognition possible.
But what drove this mutually assured safety may have actually been something selfish.
Imagine for a moment that the palm of your hand was covered in toxic needles,
and every time you touched your own body, your palm tore off a piece of it. You would probably
not last long as an organism. You would need some kind of way to tell your palm that the
thing it is touching is in fact the body it belongs to and to not try and damage it.
The same may have been true for the ancestors of Dileptus and of other organisms that have
toxicysts. They may have kept accidentally hurting themselves over and over, often beyond repair
until evolution provided a new path, one where they would be able to recognize themselves—and
perhaps eventually, even others of their own kind.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
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