Short science posts | Eluding Ctenophora

Ctenophora, commonly known as comb jellies, are a rather perplexing phylum of beautiful pelagic creatures. Their evolutionary position has been debated for many years as is the origin of their nervous system (some scientists believe they are older than sponges and that sponges lost their nervous system, while others advocate the theory about the nervous system forming independently twice, once in cnidarians and once in ctenophores).
Ctenophora have two nerve nets: subepidermal and less organized subgastrodermal, which recent research identifies as a mesogleal nerve net. Nerve cells from this layer communicate with muscles by synapses and affect the locomotion of the body. The subepidermal net is denser around the mouth, the pharynx, and under the comb rows (comb rows are strips that run the length of the ctenophore body and contain cilia called “ctenes”). Ctenophore neurons can be iso- and multipolar.


They have sensory cells on the whole surface of the body and those correspond to vibrations and thermal and chemical stimuli: more receptors are located around the mouth and pharynx. Ctenophora also have an apical and aboral sensory organ. Such sensory organ consists of a statocyst, a sensor that contains a statolith that balances on four groups of long cilia connected to the comb rows. These organs help the orientation of the ctenophore body.
What’s extremely interesting is that ctenophores use different chemical signalling system than the ones described in the previous posts, mainly because these animals simply lack the neurotransmitters (and genes), such as serotonin, dopamine, noradrenaline, and acetylcholine; glutamate is the only neurotransmitter currently known to be present.


I gathered all this information from different resources, and some are sometimes contradictory or are generalizing conclusions about the whole phylum from the data of only one ctenophora species. This is the best overview I could manage, to show both the similarities and the differences of the ctenophora nervous system, when compared to the Cnidarian system. These lovely animals are not very well researched and I’m sure many wonderful breakthroughs about their anatomy, physiology, and their place in the evolutionary tree are to come.

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
Norekian & Moroz Neural system and receptor diversity in the ctenophore Beroe abyssicola J Comp Neurol. 2019;1–23.
Ctenophores – quick guide
Did the ctenophore nervous system evolve independently?
Aliens in our midst

Reading | Savage Harvest

Today’s book I would like to share with you is Savage Harvest: A Tale of Cannibals, Colonialism, and Michael Rockefeller’s Tragic Quest for Primitive Art by Carl Hoffman. For my Twitter followers, me writing about this book is surely not a surprise – I mentioned it couple of times already, praising it both on- and offline.

As a huge true crime buff, I was intrigued by the disappearance of Michael Rockefeller and stumbled upon the book recommendation on a subreddit. I have a habit of immediately searching for the book, which led me to the Amazon store, with a discount for Kindle edition. I clicked as fast as I could on that “one-click” buy button and then… Life got in the way, as it usually is with me and books. I think almost a year has passed before I started reading it, and couple of months before I finally finished it – not because I found it boring, but because my studying, and at times, health issues, were taking up the most of my time.

Still, a true crime book and slow reading tempo don’t really equal a book review on a science blog, right? Well, that would be true, if the book was only about that. Savage Harvest is actually a blend between a biography, travelling diary, and anthropological research. I went into the book expecting to gain insight into Rockefeller’s life and death, but I learned so much about the indigenous culture in New Guinea; Hoffman also gives an astonishing historical overview of the political and cultural situation, the discovery, and tribal relations of the New Guinea.


When I was a child, I used to watch many documentaries, and the word “cannibalism” was often mentioned in rather hush tones, and as the only descriptor of certain tribes. No rituals, no gods, no traditions mentioned, just… cannibalism. By the time I started reading Savage Harvest, I was aware of the complexities that followed a culture, any culture, and especially one as complicated as the culture of New Guinea seemed to me. But reading this book, I learned so much more; the people of New Guinea weren’t some distant islanders on a spot on a map far away anymore, they became actual people, with their intricate system of believes, complicated language, and centuries-old traditions.
The book also touches on racism and culture clashes, and how, for centuries, indigenous cultures were merited through the western lenses, forced to adapt to our rules and religion; New Guinea was not an exception to this rule, as it was colonized by various European countries for years, mostly notably the Netherlands, which claimed the western part of the island.


As a non-native English speaker, I always rate a book by the flow and how easily I can understand it; this book is getting my highest praises. I also really liked how some chapters were written in the present (author’s) time, and some were purely in the past, but all of them worked perfectly in coherence. Furthermore, it’s obvious that Carl Hoffman tried to immerse himself as much as possible, in order to gain a relatively objective insight into the tribal culture he was investigating; he learned how to speak the Indonesian language and even lived with the tribe in the southwest of New Guinea, the same place which Rockefeller was visiting, collecting cultural artifacts, and ultimately disappeared from.

The whole book is, to me, a fascinating insight, and a fantastic mixture of genres that I didn’t expect to work that well together. I recommend this book to everyone who loves to read, even if they don’t have a big interest in topics this book deals with.


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If you read this book, I would very much like to hear your thoughts and opinions; did you like it as much as I did? Will this book find its way to your reading list? Let me know in the comments!

Field | Crayfish alert at Žumberak Mountains

Hi everyone, and welcome back to my blog. I took a month+ long break, during which I focused on my health and final exams at my University. At the same time, BIUS – Biology Students Association was preparing for their annual field trip, that I really wanted to be a part of!
BIUS is an association that gathers many Biology students from our department and focuses mainly on field trips, excursions, and expert lectures, all in order to complement and expand our Biology-related knowledge about certain topics. BIUS is also a publisher behind In Vivo Magazine, for which I serve as editor-in-chief.


Firstly, however, I would like to write a bit about my love for scientific (and a little less scientific) field trips. My primary love is the lab, after all. However, I grew up in a tiny village, surrounded by a living world – woods, animals, endless fields of tall grass… I actually started to think about studying something science based, perhaps Biology even, way back in the primary school, after wanting to identify all the bugs and spiders I would find in my front yard.
During my first two years of Bachelor’s degree, the thought of going out to the field didn’t really cross my mind, but it all changed in the middle of my third year, when I realized that something was lacking in my life, and that something turned out to be raw nature.

Photo by Đina Nola

This year’s big field excursion lasted for eight days, but I was only able to attend for the last four. Usually, BIUS organizes this kind of excursions twice a year, in May and September, but due to the pandemic, it was completely moved to the end of September, when situation in Croatia improved. Every year, a new terrain is explored, usually switching between continental and marine area. For this year, the leadership chose the Žumberak Mountains which are located on a border with Slovenia, and are approximately one hour drive from Zagreb. Žumberak is a mountain range divided into two parts, the Samobor Hills and the Žumberak Hills, both comprising the protected nature park Žumberak – Samobor Hills. It is home to many plant, fungal, and animal species, some of which are endangered or sensitive.


At first, shortly after arriving I was planning to spend every day with a different group, but in the end, I spent all the days driving around with the Crustacean group. I wasn’t sure how much fun is that going to be, since I knew very little about freshwater crayfish, apart from researching crayfish plague for a little while as an undergrad during an elective lab course.
I was already familiar with two members, Lena and Ljudevit Luka, since we are the same generation and took multiple classes together, and I also knew Anita and Karla a little bit; the whole group was very determined to carry out their research but with the sprinkle of carefreeness. I didn’t feel excluded for one bit and they were extremely patient with me taking photographs and filming videos.

So, what did Crustacean group actually do? Anita kindly explained their goals:

  • monitoring of the species Austropotamobius torrentium, also known as stone crayfish (how many specimens, in which streams are they located, what gender…)
  • taking swabs of crayfish cuticles in order to check for crayfish plague pathogen; this is later investigated by using the PCR method
  • taking water samples using special filters in order to check for crayfish presence; this is later investigated by analyzing the eDNA (environmental DNA)

How does that actually look like out in the field?
The first thing we did every morning, was to check the map and the roads; sometimes, we drove for more than one hour to reach a destination. Then we walked up to a stream, which sometimes proved to be rather tricky, since some seemed to dry up overnight. The most important thing we did before and after walking in every stream, creek or puddle was to disinfect our rubber boots, in order not to accidentally transfer pathogens to different habitats.

The group was very active even before my arrival, so we checked some permanent streams where they already set up special crayfish traps, that were actually made of old plastic bottles, with some tasty hot dog sausages in them. (Don’t worry, those traps are reusable! They just have to be washed thoroughly.) After taking out crayfish, one by one, they are measured and gently rubbed with a toothbrush, in a special buffer, to collect possible crayfish plague pathogen. Every tube containing that buffer is then labeled and safely stored. Crayfish are carefully released back into the stream, at the same place where they were found.

However, sometimes we went to streams for the first time, which meant no traps. So how do you catch a crayfish then? With hands. Usually they were hiding under rocks, but what most people probably wouldn’t expect, is that they are freakishly fast. Still, even during night-time catching & release, every member of the group was highly skilled in catching them. They could also easily discern female from male specimens, and Ljudevit Luka readily explained how, and also sent additional images (the ones below). In short, the main difference is that male crayfish have gonopods, while females don’t. (Gonopods are modified legs that are substantial during mating.)

A female stone crayfish

In four days that I spent with this wonderful group, I learned a lot and had a really amazing time. I wanted this post to focus mostly on crayfish, but I’m planning to post another one, where I will write a little bit more about travelling, our camping site, and wonderful nature I was able to document. I also took many videos, which I’m currently editing in one coherent, presentable, work, which I initially planned to release at the same time as this article, but life got a little bit in the way.
I sincerely hope you liked this write-up, and will read my next one as well!


Here you can find social media of some of the members of the Crustacean group, as well as the KarioAstacidae website, a student project led by Ljudevit Luka and Lena, which focuses on Astacidae populations in Zagreb.

Short science posts | Hydrozoa

Hydrozoa are the last cnidarian class I’m going to write about. They can exist in two distinct shapes, as hydromedusa and hydropolyp (same as Scyphozoa and Cubozoa). Despite perhaps expecting hydrozoans to be the most advanced in both nervous and sensory systems, they don’t actually have any rophalium. Furthermore, some hydromedusae don’t even have nerve nets. However, they have two nerve rings (outer and inner) on the margins of their bells which are regarded as ganglia by some scientists.

These rings consist of neural pathways which process different sensory inputs (such as light and gravity). Aglantha digitale, a hydrozoan species, has been reported to have as much as 14 distinct neural pathways. A. digitale is also distinct from the other species in the class by having two swimming “modes” – slow (which is a characteristic for all hydrozoan) and escape mode. Transmission through giant ring neurons is responsible for both modes, but the escape mode requires a stronger contraction. The slow swim mode is activated by the input from the pacemaker, which triggers slow calcium spikes. Direct mechanical nerve ring stimulation by tentacles triggers fast sodium spikes. In short, giant ring neurons are capable of generating two different kinds of action potentials.

bsh

Gap junctions are also present in (and only in) Hydrozoa, and they transfer electrical signals through the musculature. Furthermore, I would like to emphasize that despite some hydromedusae not having a nerve net, some in fact do, and so do hydropolyps. In polyps, however, some groupings of the neurons could be found around their mouth.

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
Do jellyfish have central nervous systems?
Jellyfish nervous systems

Short science posts | Cubozoa (most advanced cnidarian nerve system)

Cubozoa, or box jellyfish, are another cnidarian class. Their name stems from their distinct cube-like shape. Cubozoa are also distinct from other cnidarian because their venom can be fatal to humans. As with all cnidarians, box jellyfish have two nerve nets and, like Scyphozoa, rophalia. However, box jellyfish also have a distinct nerve ring, as well as more developed eyes that consist of a lens, cornea, pupil, and a layer of retinal cells. Altogether, Cubozoa have 24 eyes, which makes them the most advanced cnidarian class in the sensory aspect.

Rophalia are mutually connected via the mentioned nerve ring. This ring is believed to be an integration center for the swimming, visual, and tentacle systems; it is comprised of oversized neurons, as well as some smaller neurites.
The communication between the nerve net and jellyfish muscles is regulated by chemical synapses.

Most of the information relating to Cubozoa, I already mentioned in the previous post about Scyphozoa, so I only wanted to relay the main differences between the two. These two classes are so similar that, until recently, they were actually considered one class.

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
The ring nerve of the box jellyfish Tripedalia cystophora
Do jellyfish have central nervous systems?
Jellyfish nervous systems


Biology in popular culture – movies&TV (part 1)

I already wrote couple of posts on this topic, and today I’m focusing on several examples from movies and TV shows I’ve recently watched. The movies I’m going to write about are Lara Croft: Tomb Raider – The Cradle of Life, The Good Liar, Charlie’s Angels (2019 version), and Paranoid TV show. So, if you are planning to watch those, just a warning that there will probably be spoilers below!

Let’s start with the obvious and amusing misportrayal: in Lara Croft: Tomb Raider – The Cradle of Life (2003 movie), Lara is riding sharks in the opening sequence. I think no one would believe this is actually possible, but shark petting videos recently became very popular. However, many researches are strongly discouraging this type of behaviour.


The Good Liar (2019 movie) is an interesting thriller with really good cast that I actually enjoyed. Without giving out too much of the plot, I’ll just mention one scene where Helen Mirren’s character gives the haircut to the character played by Ian McKellen. She uses cut hair for the DNA analysis, factually linking McKellen’s character for the past crimes.
Of course, we all know that without the root, there is no DNA to analyze, right? Not quite.
Most companies that do DNA analysis require hair with follicles in order to extract DNA for analysis; however, they mostly deal with paternities, so they need the nuclear DNA. Mitochondrial DNA, on the other hand, apparently can be extracted from the hair itself. For the movie’s purposes, I think nuclear DNA was needed, so this seems like a movie mistake. But, recently scientists did manage to successfully extract nuclear DNA from rootless hair, but that DNA is often fragmented and complicated to extract.
I would also just like to mention that I believe this movie explains trauma and coping surprisingly well for a Hollywoood movie.

In Charlie’s Angels (2019 movie), which I hoped would be more enjoyable than it was, a very interesting premise was introduced; in order to effortlessly communicate, members of the team get a certain tattoo (at least I think it’s a tattoo, but don’t 100% quote me on that) and they can hear thanks to it. So, my first thought was, wow, they really went sci-fi on this one, but it sounded too out there. And then I remembered bone conduction. Simply, bone conduction allows you to hear the transmission, without blocking the outside sounds. And yes, only you can hear it. There are headphones already in use for this type of thing, and they can be also used to help with some kinds of hearing impairments. These headphones are placed on the skull, and I haven’t seen it implemented in a tattoo yet, but it’s actually a neat idea.

Paranoid (2016 TV show) is, in my opinion, really bad, despite only tangential connection to Biology. This show feel anti-medication and anti-psychiatrists, portrays them in a very bad light, and chooses not to mention how much medications and psychotherapy are actually helping people. The premise is also built on one of the cliche “anti-big pharma” representations. I was honestly insulted, despite not working in any of these fields. There is a also a subplot concerning a female character who had provocative photos of her taken 15 years ago, and she is not longer in possession of said photos; she is blackmailed with the possibility of leaking those. Her love interest immediately accuses her of things I won’t write here, but you get the main idea. I mean, am I the only one who sees this as highly problematic
This TV show is doing some serious damage to the health care, it is insulting to physicians, it is insulting to patients, and I honestly can’t believe that no one during the whole production didn’t say anything.


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I hope you like these kind of posts, because I already have enough material for another one (there are a lot of Biology & science mistakes on the big screen). What is your favourite movie mistake related to Biology?

Short science posts | Scyphozoa – more advanced nervous system

Scyphozoa (true jellyfish) are much more interesting (in a neurobiological way) than previously described corals. One major difference is that Scyphozoa are pelagic animals, which means they are not fixed to the ground. They also have two diffuse nerve nets (subepidermal and subgastrodermal) that consist of bipolar and multipolar neurons – the impulse conduction has been measured at 0,15 m/s. Both nets coordinate the movements of an animal towards the food. Some scientists, however, differentiate one diffuse and one motor nerve net. The motor net is in charge of the activation of muscle contractions after receiving signals from the so-called pacemaker organs (which are in charge of the swimming rhythm). The diffuse net, in this case, is in charge of marginal tentacle contraction and it is also believed it communicates sensory information to jellyfish musculature. Neurons of the motor nerve net are connected by chemical synapses, while neurons of diffuse nerve net are connected by peptidergic synapses that were noted in Anthozoa as well.

Sycphozoa also have much more developed sensory organs than any of the animals previously mentioned. These sensory structures are called rhopalia and they are located on the edges of the jellyfish bell – there are usually four of them (or a number that’s a multiple of four). Rhopalia contain multiple sensory receptors – statocyst (balance receptor), ocelli (light sensitivity), a mechanoreceptor, a chemoreceptor, and aforementioned pacemaker neurons.

I would also like to note here that some authors (I’m referring here to the article “Do jellyfish have central nervous systems?” by R. A. Satterlie) believe this kind of nerve net explanation is rather simplified and that there exist some evidence suggesting that jellyfish have a centralized nervous system, mainly that rophalia are in fact rudimentary ganglia and could be regarded as integrative centers. However, any communications between rhopalia themselves exist only through the nerve nets.

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
Do jellyfish have central nervous systems?
Jellyfish nervous systems

Short science posts | What is a nerve net?

A nerve net is a type of nervous system that consists of many neurons but there is no brain or cephalization. Nerve nets are found in animals with radial symmetry (Cnidaria) and biradial symmetry (Ctenophora). Despite being called a net, there sometimes exist some groupings of neural cells in some Cnidaria classes, which I will write more about during the next couple of weeks.
Cnidaria are specific due to their specialized organelles, cnidocytes, which they utilize to hunt for food or use for securing itself to a surface. Some cnidocytes contain toxins that can paralyze their prey (the burning sensation you may have felt when touching a sea anemone 😉).
As a rule, Cnidaria have two diffuse nerve nets, one in the epidermal layer and a second one in the gastrodermal layer. In between these two layers is the mesoglea, a layer that functions as sort of a skeleton. The epidermal net consists of bipolar and multipolar nerve cells, while the gastrodermal net is made up of only multipolar cells.

Cerianthus membranaecus (known as cylinder anemone or coloured tube anemone)

Cnidarian nerve systems are fascinating but also quite unexplored. What is known is that nerve cells consist of two types of neurons, sensory neurons that respond to stimuli and motor neurons which ultimately trigger a response. Chemical synapses exist and provide the communication between the neurons. Hormones have also been reported in some cnidarians (steroids, neuropeptides) but it is still not known how exactly these signalling molecules work.

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In the next couple of weeks, I will write a post about every cnidarian class and also ctenophores, focusing on their nervous and sensory systems. If you have any questions or would like me to focus on something, please let me know!

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
Endocrine-like Signaling in Cnidarians: Current Understanding and Implications for Ecophysiology
Evolution of sensory structures in basal metazoa

Reading | Blood Work by Holly Tucker

Blood Work: A Tale of Medicine and Murder in the Scientific Revolution by Holly Tucker is a book that I first read almost 10 years ago. I got it as a gift from a dear friend, for my birthday during the time I was a student at School of Medicine (as you can guess, I decided to start anew and switch to Biology). However, this book has always stayed with me, not only because it was the first book of this genre I’ve read – I loved it because I thought it was the perfect mix of history, medicine, and macabre.

Blood Work follows a fascinating tale of the history of human transfusion, something what in today’s world we almost take for granted. Back in high school, we learned all about Rh factor and blood types (and how there is a possibility of A and B parent having an O or AB child) and voluntary blood donations are common occurrence in my country. Despite all this, I never wondered when did the actual blood transfusion procedures start and how did physicians know whose blood to use.

In the book, we follow Jean-Baptiste Denis, a 17th century French physician who administrated first documented transfusion. Since this transfusion included using sheep’s blood, it was called a xenotransfusion, which is a term that describes blood transfusion from one species to another. This experiment was successful, probably due to small amount of transfused blood and, I dare say, luck, since at the time, blood groups and agglutination were not known facts.
Denis’ last transfusion experiment is, however, the one we learn about in a detail – after trying to treat an illness of psychiatric nature, and transferring a large amount of calf blood, his patient dies, and he is accused of murder. Denis was ultimately acquitted (with a true crime worthy twist in the case), but all further transfusions were banned, first by French government, then by English and even the Pope.

Blood Work doesn’t focus solely on this event – the writer masterfully describes political events of the time, both in France (rivalry with another physician, Henri-Martin de la Martinière, tensions in French Academy of Sciences founded by Louis XIV) and abroad (a competition between French and English Academies), as well as the religious ones (“playing God”, fear that this kind of transfusion could produce some sort of half-human half-animal creature). Furthermore, as Neil Blumberg wrote in his review for Journal of Clinical Investigations, these kinds of experiments were primary conducted due to the belief that transfusion could treat, or even cure,  mental illness, sometimes we now know is not possible.

Lastly, it doesn’t actually matter if you have health and/or science background to find this book interesting, as long as your’re interested in history and historical non-fiction. Blood Work offers a captivating look on the beginnings of one of the most important medical procedures in the world and does it so vividly you almost feel like you’re transported to Paris, in the middle of the scientific revolution.

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I would very much liked to hear your opinion – did you read this book, and if yes, did you like it as much as I did?
Do you have similar book recommendations?  Please let me know in the comments 🙂

Short science posts | Nervous system evolution

For the next couple of weeks, I would like to write a bit about the evolution of the nervous system, from early nerve cells to the human nervous system and brain evolution. Alongside nervous I will also focus, to a lesser extent, on sensory systems. These posts will be published on my Instagram account, but I decided to publish them on the blog as well.

Mostly, these posts will be about various animals and the nerve systems they have – nerve nets, nerve cords, complete systems. The main process behind this is called cephalization, and it starts with the groupings of nerve cells and ganglia at one end of the body. After some (long) time, this process led to us having a head with sensory organs and a brain inside it.

But when did all of it start? It is kind of hard to say, for even single-celled organisms, such as bacteria, have voltage-gated channels and genes that support the theory of possible synaptic transmission. These channels are potassium (the oldest), calcium, and, rarely, sodium channels as well. Action potentials have been detected in some algae and diatoms, although their function is mostly unclear. In Chlamydomonas (unicellular green algae) on the other hand, potentials were detected in flagellums, which clearly suggest they play the part in the movement of the algae. Action potentials were also recorded in the cilia of some protists, such as Parmecium.

Of course, the exact evolutionary processes are unknown, and there is a possibility that these organisms acquired the mentioned features later than scientists now assume. It is also possible that some more evolved organisms, such as sponges, subsequently lost some of the features discussed here (more about this in the next week’s post).

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
Bacterial voltage-gated sodium channels (BacNaVs) from the soil, sea, and salt lakes enlighten molecular mechanisms of electrical signaling and pharmacology in the brain and heart
Early evolution of neurons
Deep evolutionary origins of neurobiology
From damage response to action potentials: early evolution of neural and contractile modules in stem eukaryotes