This episode is sponsored by 80,000 Hours. 80,000 Hours is a nonprofit that aims to help people have
a positive impact with their career. Head to 80000hours.org/microcosmos to start planning
a career that could potentially help solve one of the world’s most pressing problems.
What you’re watching right now is something that James, our master of microscopes, had never seen
before. And given how much of the microcosmos he’s watched, anything that’s new to him is thrilling
to us. What he’d found were those two Loxodes you see stuck together, waltzing around in a
very public display of conjugation. While there are ciliates that frequently dally around
in sexual reproduction, for others—including these Loxodes—it’s just not a common sight.
So James kept his camera focused on them, following their progress.
But in the process of watching this population of Loxodes, James would find something much stranger
going on in the microcosmos. Something that would start innocently enough,
but that would end up in a place far darker than he had anticipated.
The scene in front of you now is filled with loxodes, more of those freshwater ciliates
we were just watching. The smaller species are called Loxodes striatus,
and the larger ones are called Loxodes magnus. And that’s what we’re following around right now,
a Loxodes magnus navigating a field of debris and other organisms.
But why? In a screen full of these organisms, why are we following this one?
Well, this Loxodes magnus is large—so large that it was able to eat a rotifer,
those funny animals we often see getting bullied by their single-celled neighbors.
And James meant to quickly capture another one of those instances before moving on. As the Loxodes
turns, you can sometimes see the outline of the rotifer taking up space in grayish oval area.
But what James realized as he was watching—and maybe you’ve caught on to this as well
that rotifer is moving. It’s alive, twisting and turning inside of
the food vacuole it’s been stuffed into. And when James realized that, he had to keep
recording. Because there are stories out there of rotifers fighting back. Of them stretching
themselves and piercing away at the ciliate that had the gall to eat them until finally,
they poke through the body that’s attempting to digest them and escape. So yeah, James wanted to
see if he could watch that happen, to see if he could watch the rotifer triumph for once.
If only it were that easy. But that’s getting ahead of ourselves. Let’s just sit here for a
bit and watch the rotifer at work. This is one of those episodes where I’ll be quiet for a bit
and then chime in as the rotifer’s journey takes shape. And for now, the story is straightforward.
The rotifer It tumbles and stretches, and the shape of its captor shifts in response,
expanding in width as the rotifer refuses to be digested.
If it seems like the rotifer is sometimes putting up less of a fight,
you’ll have to excuse it. The conditions it is facing inside the Loxodes’ food vacuole are
intense, a bath of acid meant to eat away at its body and render all its multicellular complexity
into a well-digested stew. The fact that it has survived this long seems like a small miracle.
At this point, the Loxodes is passing alongside a field of rotifers—the sisters of the very rotifer
the Loxodes is trying to digest, And you can see them making that same telescoping motion
as their trapped sibling, just from the anchored safety of a piece of debris.
Perhaps it seems like the rotifer is making all this movement for nothing, but just wait…
This. This is the moment where the rotifer’s escape begins in
earnest. It managed to tear a chunk out of the Loxodes, ripping out an escape route
that the rotifer’s head can start to peek out of.
Just watch as it keeps that movement going, the gaping hole in the loxodes growing larger and
larger as the rotifer continues its work. The Loxodes seems unperturbed,
continuing to swim as if its insides aren’t being torn apart. But with enough time and enough poking
and prodding, the rotifer escapes its acid prison, making its way once more into the microcosmos.
This is a moment to celebrate, right? We’ve been watching this rotifer try and try
and try for minutes, and here we are now, with all the success to show for it as it
sets up a new home for itself. That’s what James thought too,
except that he quickly realized that something was wrong. The rotifer wasn’t alone. It was actually
inside another rotifer, or rather what had once been a rotifer—what had once been its mother.
The acids of the Loxodes’ food vacuole had eaten her body away, digesting and decomposing it
until all that was left was an exoskeleton that protected the young rotifer living within her.
While rotifers hatch from eggs, there are species that hatch from eggs that are still
tucked away inside of their mothers. This trait is called ovoviviparity,
and it’s found in various amphibians, insects, and sharks…and yes, rotifers like this one,
using their body to shield their young. And yes, the young rotifer survived.
But as James watched, a more cruel truth emerged: the young rotifer was stuck. The same cuticle
that had protected the rotifer from the acids of the loxodes would now hold it forever,
rigid and uncaring to its former life as that rotifer’s mother.
The next day confirmed the valiant young rotifer’s tragic end,
stuck within the confines of its mother’s cuticle
there towards the bottom of your screen, no longer pushing and shoving, but motionless in death.
And as for the Loxodes, we don’t know what happened to it. But given the
capacity of its family for regeneration, it probably survived with little injury.
Perhaps it swam by its former meal, unaware of their previous encounter
a battle waged, a battle lost, and the world moving on around them both just the same.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
And thank you again to 80,000 Hours for sponsoring today’s episode.
80,000 Hours is a nonprofit that aims to help people have a positive impact with their career.
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