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Tardigrades are famous for their capacity to survive. If you look them up, you will
be inundated with long lists of the many things scientists have thrown their way to see if the
tardigrade will survive. We’ve made some lists like those ourselves. Tardigrades on the moon,
tardigrades in extreme heat. You’ve heard about them. We’ve talked about them. What else is there?
Well, here’s a surprising fact you might not have known. For certain species of tardigrades,
like the one in the middle of your screen right now,
you can tell the difference between a male and a female by looking at their toes.
That’s right. The toes. These tardigrades are called Milnesium,
and the males of these species have a pair of claws on their feet that are shaped a little bit
differently from the rest of the claws, with only one hook on each claw instead of the usual two.
But after taking a closer peek at this tardigrade’s toes,
we can confirm that she is a female tardigrade. Now, that’s a fun fact for us as we watch
the clip. But it does not actually do anything for the poor rotifers that are
surrounding this tardigrade, who are currently stretching themselves in and out of danger.
Around the tip of a tardigrade’s mouth are small bumps that we think act like little sensors.
And when those bumps make contact with a rotifer, out pops the tardigrade’s stylet—a needle that
pokes out from the tubular mouth opening. That stylet pokes into the rotifer,
and from there the tardigrade uses a circular structure called a pharynx in its head
to create strong suction. And then, the stylet goes from functioning as a needle to functioning
as a portable, built-in straw that lets the tardigrade suck out the inside of its prey.
You can see some of the bodily fluid leaving the rotifer as the tardigrade’s stylet pumps
away like a beating heart. And when she is done, the rotifer remains, like an empy coffee cup.
This method of eating works quite well for the tardigrade, letting her eat quickly from
the prey that is directly in front of her. But not all organisms come equipped with a
weapon that lets them turn rotifers into Capri Suns. These organisms have to turn to other
methods to extract nutrients from their food. This marine ciliate is called kentrophyllum, and
it came to James, our master of microscopes, in a large container full of beach sand. On a normal
day, maybe we would talk more about its funny almond shape that stretches as it swims around.
But today is not a normal day because this kentrophyllum is
about to be overshadowed by a rotifer. Now, where is the rotifer, you might ask?
It is inside the kentrophyllum, of course. We did not catch the moment of its capture,
when the toxic needles lining the kentrophyllum darted out and paralyzed the rotifer. By the
time we arrived, the rotifer had already been ingested…but it was not dead yet.
You can see it wiggling and wrestling at the broad end of the kentrophyllum,
causing the ciliate’s body to wrinkle and fold in on itself. But it is trapped inside
of a food vacuole now, a compartment that exists to break this rotifer down.
Sure, the rotifer can try and fight against the walls of the vacuole holding
it hostage. But there’s not much it can do against the digestive enzymes pouring in,
or the increasing acidity of its surroundings. A food vacuole is a hostile place to be, and for
minutes, its destructive tools will go to work. In the end, the rotifer will be left in dissolved
pieces to be absorbed by the kentrophyllum’s cytoplasm, sustaining the organism that
was the site of its last battle. It’s a lonely death for the rotifer,
with only the kentrophyllum to witness it. Though I suppose now there is also us, sharing
and immortalizing that rotifer’s last moments. And if the rotifer had not died in the body
of another organism, it may have ended up like this gastrotrich.
Now to be fair, they did find themselves in a very similar situation: they are both dead.
But the rotifer was eaten alive, digested from the outside while trapped in another organism.
Meanwhile, this gastrotrich is going through the exact opposite situation. It is being eaten from
the inside out, by a scavenger called a peranema. Now, as far as we know, the peranema didn’t do
anything to kill the gastrotrich. It was likely already dead, though we don’t know what killed it.
But the peranema is both a hunter and a scavenger. Sometimes it can be found with other peranema as
they hunt down prey, in a pack of hungry microbes. At other times, the peranema scavenges. They
are notorious for being able to squeeze their way into whatever
holes they find to get into a dead organism. And in this case, the gastrotrich’s exoskeleton
was the right combination of available, open, and dead for the peranema, which found its way
in and decided to begin helping itself to the buffet of dead tissue around it. After all, the
gastrotrich won’t be needing that tissue anymore, so the peranema might as well make good use of it.
The gastrotrich’s body has likely vanished by now. Perhaps the peranema will have
finished it off entirely, or some other scavenger will have joined in on the fun.
Or perhaps, it will have simply faded, like the rotifer inside the kentrophyllum,
its body eventually fading into the world that encapsulates it.
But for this last moment, let’s remember the gastrotrich in a more beautiful moment
under a fluorescent light, glowing in the glorious purple autofluorescence of its remains.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
And thank you again to Wren for sponsoring this episode of Journey to the Microcosmos.
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