This episode is sponsored by Surfshark. Get Surfshark VPN at surfshark.deals/microcosmos
and enter promo code microcosmos for an 83% discount and 3 extra months for free.
Rotifers don’t really get a lot of love when it comes to microscopic animals.
At least as far as the public imagination goes,
the rotifer is overshadowed by its fellow metazoan of the microcosmos: the tardigrade.
And we might be part of the problem. In the first few months of the channel, we did spend an entire
episode on our rotifer friends. But despite how often they show up in our videos, spinning
their wheels, we have many more videos focused on tardigrades…and we even made a tardigrade T-shirt.
Of course, there is a very simple explanation for this. Tardigrades are weird-looking,
but they’re also kind of cute. At times, they may even seem kind of cuddly.
Rotifers, on the other hand…well, they’re mostly just weird. Very cool, but also very weird.
But rotifers are making a bit of a comeback—a very literal one. This year, researchers announced that
they were able to recover a living rotifer frozen inside 24,000 year old permafrost
collected from a river in northeastern Siberia. While some species of rotifers have been noted
for their tardigrade-like ability to withstand long periods of low temperatures, scientists had
previously observed those periods to be more on the order of 6 to 10 years. That’s still a pretty
impressive amount of time to survive freezing conditions, but it’s a far cry from 24,000 years.
This doesn’t mean that we should be expecting ancient rotifers to be popping out of the
ground or anything. It’s just that it’s so remarkable to imagine a world where
tardigrades aren’t alone in their complex bodies and resilient capabilities…and then to realize
that world isn’t imaginary. That rotifers have been right there alongside them the whole time.
And so today, we want to take a moment to appreciate the rotifer from the inside
out. With many animals, that would require dissection. But fortunately for us,
a little bit of strong light and our most recent microscope updates lets us see the
inner machinations of the rotifer at work. It’s almost like we’re on a field trip,
huddled together on some kind of magic school bus as we journey through the organism itself.
All around us is a living exhibit made up of around 1,000 cells.
That number of cells will stay constant over the course of the rotifer’s lifetime.
But there are also about 2,400 known species of rotifers,
which means there have been at least 2,400 ideas of just how to put 1,000 cells to good use.
So what we’ll be seeing today are just some of those uses. Because it turns out, there
are many many many different ways to actually be a rotifer and to actually look like a rotifer.
But different as they may be, there are a few traits that unite these strange
swimming organisms—including what will be the first stop on our tour.
This is the corona, the moving, hairy crown atop the rotifer
that gives it the name “wheel bearer.” It will look different for different species, but this
spinning headband shares one specific purpose: to stir up the water and bring food to the rotifer.
Then the food will pass on to another part shared by all rotifers:
their jaw, also called the trophi, which is settled into a muscular structure
called the mastax. You can see it at work here, opening and closing inside the rotifer’s head
as it passes food from the head to the rest of its body.
Jaws have evolved many times in the animal kingdom over the past 500 million years or so,
which means that you can find a lot of different jaws out there in the wild.
Even among rotifers, there are at least 9 different types of trophi that we know of,
and their shape depends on the diet of the rotifer.
And as you look around at the trophi, what you’re seeing is an engineering marvel.
There are at least seven distinct parts to it, each with their own set of actions that
they perform over the rotifer’s lifetime without wearing down or breaking. They grab, they crush,
they pierce. It’s like a tiny little machine inside the rotifer, which is why
researchers have even looked to the trophi as inspiration for future tiny little robots.
Does that mean we can expect a rotifer robot any time soon? Probably not.
But who needs robots when we’ve got the real live thing right here in front of us?
The trophi’s main purpose is to pass food from the outside to the inside, which takes us to our
next—and perhaps most perilous—stop, the stomach, with its enzymes designed to break down food.
Though…if the rotifer is male, you might not actually have to watch out after all because
there might not be a stomach...because they just don’t live long enough to need one.
Rotifer species differ in how they approach the necessity of males. There are some that have
done away with the concept of males entirely, relying on asexual reproduction to survive.
Others will keep them around for a short time, though primarily for sexual reproduction.
These male rotifers are smaller, and their survival lasts just
long enough to allow them to fertilize eggs. So returning our attention to the female rotifer’s
body, we can see the oocyte in the ovary, nested in a tissue called the vitellarium. When food
is plenty, the vitellarium can provide RNA, protein, and liquid droplets to the oocyte, so
that it swells and swells, pushing the rest of the organs around until finally the egg is released.
The last stop on this tour de rotifer is the foot, which even extends into a toe. But unlike
our toes, the rotifer toe has a cement gland in it, producing a glue that keeps the rotifer
stuck to whatever surface appeals to them. At least, that’s the case for many rotifers,
as they stretch out from a single anchor point and put their frantic crowns to work.
But some rotifers don’t want to be tied down. They prefer a more mobile lifestyle. These planktonic
rotifers might end up in the open waters where there isn’t much vegetation to crawl around on
or to stick to. So they just don’t. They might forego a foot altogether.
Instead, they swim around, on occasion even using the cilia on the crowns to help them.
But if they bump up against a predator or something else that makes them uncomfortable,
they can do something you might not usually imagine rotifers doing. They jump.
They can do this because they have paddles. To see them, we have to return to where we started,
to the front of the rotifer, where these striated blades make up the planktonic rotifer’s jumping
apparatus. They work incredibly quickly, taking only about 7 milliseconds to get going
if a rotifer has made contact with a predator. As we’ve travelled through the rotifer’s body,
we’ve seen just how much can be made with so little. And should we live in a future filled with
resurrected ancient rotifers and robotic modern ones, then perhaps we will appreciate them—not
for the cute tardigrades they aren’t, but for the intricate little living machines that they are.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
And thank you to Surfshark for sponsoring this episode.
Streaming rights are complicated and some of your favorite shows might not be available to
you based on your location. But with a VPN you can access movies and shows that are only available in
other countries from wherever you are by using VPN servers in the countries where they’re available.
So, say I want to get into the Halloween spirit and want to watch the first Friday the 13th movie.
Well, it’s not currently available on any US streaming services, but it is on Netflix in
New Zealand. So, with Surfshark, I can connect to a VPN server in New Zealand and just like that,
I’m on my way to Camp Crystal Lake. One subscription allows you to install
and run Surfshark on an unlimited number of devices at the same time, and Surfshark’s
30-day money-back guarantee gives users plenty of time to try out their service risk-free.
So if you’d like to check out Surfshark VPN you can go to surfshark.deals/microcosmos
and enter promo code microcosmos for an 83% discount and 3 extra months for free.
The names on the screen, those are our Patreon patrons. And we’d like to thank each and every
one of you who has chosen to support this channel. And if you’d like to become one of those people,
you can go to patreon.com/journeytomicro. If you want to see more from our Master of
Microscopes James Weiss, you can check out Jam & Germs on Instagram or also on TikTok.
And if you want to see more from us, there is always a subscribe button somewhere nearby