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Comb Jellies take on 150 years of the Neuron Doctrine

When it comes to the nervous system, you might think we’ve got the basics down. After all, it’s been over a century since the great Santiago Ramón y Cajal proposed the neuron doctrine, which basically said that the nervous system is made up of individual, discrete cells called neurons. As you may recall from our neuropharmacology experiments, Ramón y Cajal argued for discrete cells (neurons), while Gogli thought that the brain consists of groups of continuously connected cells (reticulum). Santiago’s hypothesis, known as “The Neuron Doctrine,” was later confirmed by the invention of the electron microscope, which let us see these neurons and their connections in all their glory.

But now it looks like the fight is still on! New research on ctenophores, those weird, squishy marine critters that look like a cross between a jellyfish and a feather duster, is shaking up the status quo.

The importance of these jellies cannot be overstated. As one of the first animal groups to branch off on the evolutionary tree, studying ctenophores can provide us with clues about the very origins of animal life. And while these guys have no brains, they do have a nervous system consisting of a “neural net” – a type of nervous system organization that is very understudied. Could it be that a nervous system evolved twice, independently, in our animal ancestors? That’s the question these researchers were asking.

To get their answers, a group of European researchers led by Dr. Kittelmann at Oxford Brookes University turned to high-pressure freezing-fixation techniques and a method called serial block face scanning electron microscopy (try saying that five times fast!). This gave them a stunning, 3D view of the ctenophore’s nerve net. And what they found was quite unexpected and they shared it with the world in a recent Science paper [Burkhardt et al., Science 380, 293–297 (2023)].

Unlike our own nervous system, which comprises separate neurons connected by synapses, the ctenophores’ nerve net looked more like a reticulum – a continuous network of interconnected cells. Instead of discrete neurons with synapses (small gaps between the cells), the ctenophores have a nerve net where all the nerve cells seem to be part of one, big supercell. It’s kind of like comparing a bunch of individual houses to a giant apartment complex. As seen in their figure below, the 5 separate neurons of the nerve net are actually all fused together (highlighted in white asterisks for links between neuron 1 and 2).

Neural Net with connections

In the world of nerve nets, this is a pretty big deal, as it suggests that there’s more than one way to build a nervous system and that different animals might have taken different paths in their evolution to encode information and guide behaviors. The ctenophore nerve net is not just a simple precursor to our own complex brain but a complex and unique structure in its own right.

This opens up a whole new perspective on how nerve nets and nervous systems function and evolve, and reminds us that even long-held truths in science can change upon new evidence. So next time you see a ctenophore, don’t just marvel at the beauty of the squishy color-changing blob. You can also admire its nervous system that’s every bit as complex and fascinating as ours, just in its own, unique way. And who knows? Maybe we’ve got more in common with these jellies than we think. There’s so much more to be discovered!

Two 99 Million-Year-Old Cockroaches Found in Amber – and They Uncannily Resemble Modern Roaches

Kafka couldn’t have imagined it better. Two specimens of the cockroach phylum were going about their business in a Myanmar cave about 99 million years ago. One day they got trapped in tree resin, which then turned to amber and preserved their little bodies to this day to tell us an impressive tale of time, life, death, and metamorphosis.

99 million-year-old cockroaches
Source: Gondwana Research

Both belonged to the Nocticolidae family, which comprises a couple dozen cockroach species inhabiting caves and caverns. Our small but hardy hairy-legged friends probably even managed to survive the mass extinction event that killed off the dinosaurs along with three-quarters of all life on the planet. The researchers, who recently published their findings in Gondwana Research, labeled the two fellas “the only known dinosaur age cave survivors”. It goes to show that cave roaches are far older than we used to think. Before this discovery, it was commonly held that they date back to 65 million years ago (the Cenozoic era).

From now on, we should know better than to underestimate them.

Let’s Get to Know Them Better!

The two species now carry the names of Mulleriblattina bowangi and Crenocticola svadba. While being pretty similar to each other, the Mulleriblattina seems to have been confined to the cave life, whereas Crenocticola was a bit more curious and probably ventured outside the cave.

The planet was not a friendly place back in the Mesozoic era. But our roaches didn’t seem to mind. Resilient as they were, they developed adequate traits that would allow them to thrive in damp and dark cave environments where no other creatures are known to have existed back then. Their very long antennae allowed them to better explore their gloomy surroundings, where eyes were almost useless. The wings got stunted since they no longer needed them. The insects weren’t brown or black like their modern-day domestic relatives, but yellowish or even transparent. What use is color anyway in a place that never gets any light?

What’s even more amazing is that all of those features make the Mulleriblattina look strikingly similar to its modern cave relatives. Some things never change, and neither does the roaches’ penchant for darkness.

Scary or Not So Scary?

By this point, you’re probably beginning to wonder about their size. No reason to shiver on that account! They were actually very small – just under 5 mm (roughly 1/4in). That wouldn’t make you cringe to the depths of your soul now, would it?

The length of their limbs probably would though. Especially the cerci (a pair of appendages protruding from underneath the bug’s rear end), which were significantly longer than in your average domestic roach.

But what did they eat? While the dinosaurs were still there, these two beauties may have feasted on their droppings that they would have found near the cave entrances. Once the gigantic reptiles went extinct, they probably made do with bats’ poop. How’s that for adaptability? The scientists even spotted some particles of undigested food in their lower abdomen. Ew!

There’s another mystery the researchers had to face. How did the tree resin make it into the cave to form amber? There is no exact answer. It probably poured down through cracks and crevices on the cave’s roof. Nature sure is resourceful while taking its course.

Mulleriblattina bowangi
Mulleriblattina bowangi – Source: Gondwana Research

Let’s Get Serious for a Moment… Could We Operate on These Ancient Bugs?

You guessed right – this beautiful story about ancient roaches trapped in amber is particularly exciting for us roach-loving nerds at Backyard Brains. As you may or may not know, we’ve been harboring a lifelong appreciation and even love for roaches of all shapes, sizes, and ages.

So it’s only natural that our first thought after reading the Gondwana Research paper was whether a Mulleriblatina or a Crenocticola could possibly carry a RoboRoach backpack. Alas, both were small and, frankly, too fragile for so heavy a burden. (Okay, maybe we could build a peewee backpack for them to sport). Our next concern was: if they lived here and now, would they readily lend themselves to one of our experiments? We weren’t happy with the answer. Their legs would have been too short and slender for us to operate on.

Our “Discoid” cockroach carrying the Roboroach Backpack

In fact, the longer cerci might even provide for new opportunities to record and stimulate the nervous system of the cockroach in interesting ways! Researchers have already used our SpikerBox kits to record from the cerci, and we even had a summer research fellow pursue a research project for a version of the RoboRoach which could control EVERY direction the roach moves by stimulating both the antenna and cerci.

The third thought was a sensible husbandry dilemma: would they want to even taste some of our lettuce or carrots for that buffet-style dinner? (It’s tough to get ahold of an ounce or two of dinosaur guano these days.) That one went unresolved.

Do They Resemble Our Domestic Roach?

After all, we have to acknowledge both the similarities and differences between, say, your average Periplaneta americana (American Cockroach) and these two antediluvian beauties. All roaches are fond of gloom, and all of them are apt survivors. There’s hardly such thing as picky eating among this crowd! Those are traces of their common, eons-old ancestry. It dates back 300 million years ago, to the time before the ancient supercontinent Gondwana broke up to huge chunks of land now known as Antarctica, Africa, South America, Australia, India.

But they are also mutually different. The American roach is your regular cohabitant that you may notice as it forages through your dimly lit basement. Even though it likes darkness, it will still tolerate some traces of light – that’s how much it loves your bread crumbs or even your dandruff! And luckily for our experiments that include bug leg surgery, it boasts a giant size compared to its distant relatives Mulleriblattina and Crenocticola. Its 1.6 inches of length is just enough to scare the wits out of you as it scuttles across your dinner table. It’s also known to be a genius in the evenings and a moron in the mornings. (Which makes us think that our cave-dwelling roaches must have been Einsteins!)

So next time you reach for your phone to dial pest control, think twice. Maybe it would be more ethical to let those little guys carry on with their lives. Some of them might even make it into history books one day.