Rotifers!

 How the Bdelloid Rotifer Lived for Millennia—Without Sex

by Nina Munteanu 

 

As a child, I always wanted a microscope.

I would have collected slimy waters from the scum ponds and murky puddles near my house. I would have brought them home and exposed them to the light of my microscope. I would then have peered deep into a secret world, where shady characters and alien forms lurked and traded.

It would be many years, when I was in college, before I finally witnessed this world—so alien, it might have inspired the science fiction books I wrote later as an adult. As it turned out, I was led to pursue a Masters of Science degree, studying periphyton (microscopic aquatic communities attached and associated with surfaces like rocks and plants) in local streams in the Eastern Townships of Quebec.

While my work focused on how diatoms (glass-walled algae) colonized surfaces, micro-invertebrates kept vying for my attention. Water fleas (cladocerans), copepods, rotifers, seed shrimps (ostracods) and water bears sang across my field of vision. They flitted, lumbered, wheeled and meandered their way like tourists lost in Paris. But this wasn’t Paris; I’d taken the blue pill and entered the rabbit hole into another world...

 

The Secret—and Dangerous—World of Micro-Organisms

Small freshwater habitats are home to a highly productive and diverse collection of micro-invertebrates—multicellular animals that can barely be seen with the naked eye. Many average from 0.5 to 1 mm in size and resemble little white blobs; however, a scholar can distinguish each invertebrate by its unique movement. For instance, when presented with a jar of pond water, I can usually distinguish among the wheel-like wandering of a gastrotrich, dirigible-like gliding of an ostracod (seed shrimp), the vertical goldfinch-style “hopping” of the cladoceran (water flea) as it beats its antennae, or the halting-jerking movements of copepods (oar-feet) as their antennae drive them along like a dingy propelled by an amateur oarsman.

Alas, puddles, ephemeral ponds and vernal pools pose sketchy habitats, given their tendency to appear and disappear. These environments are ever-changing, unstable, chaotic and unpredictable. Yet, anyone who has studied these ecosystems understands that they team with life.

When a puddle or ephemeral pond dries up then reappears with rain, how can these communities thrive? Do they all die off and then somehow recruit when the pond reappears? Many of these invertebrates have evolved creative ways to survive in very unstable environments. Some form a resting stage—a spore, resting egg or ‘tun’—that goes dormant and rides out the bad weather.

Animalcules & Sleeping Rotifers

Rotifers are cosmopolitan detrivores (they eat detritus) and contribute to the decomposition of organic matter. Rotifers create a vortex with ciliated tufts on their heads that resemble spinning wheels, sweeping food into their mouths. They often anchor to larger debris while they feed or inch, worm-like, along substrates. Some are sessile (attached), living inside tubes or gelatinous holdfasts and may even be colonial. Others move about and may temporarily anchor themselves as they feed. Rotifers include species that alternate sexual reproduction with asexual reproduction, depending on environmental conditions.

Bdelloid Rotifer as photographed by Bob Blaylock

In 1701, Antonie van Leeuwenhoek observed that “animalcules” (likely the bdelloid rotifer Philodina roseaola) survived drying up and were “resurrected” when water was added to them. He’d discovered a highly resistant dormant state of an aquatic invertebrate to desiccation.

Dormancy is a common strategy of organisms that live in harsh and unstable environments and has been documented in crustaceans, rotifers, tardigrades, phytoplankton and ciliates. “Dormant forms of some planktonic invertebrates are among the most highly resistant … stages in the whole animal kingdom,” writes Jacek Radzikowski in a 2013 review in the Journal of Plankton Research. Radzikowski describes two states of dormancy: diapause and quiescence.

Diapausing results in the production of a dormant egg or cyst whose thick envelope or shell protects it from drying, freezing, mechanical damage, microbial invasion and predation, UV radiation and harmful chemicals. Many survive being eaten and can resist vertebrate digestive enzymes, helping them disperse and colonize isolated water bodies. Diapause is controlled by an internal mechanism that is initiated by various cues, such as temperature or photoperiod. In short-lived organisms, it is typically initiated only in a single ontogenetic stage. “Breaking of diapause requires specific cues, and not necessarily the return of favorable conditions,” writes Radzikowski.

Quiescent dormancy does not involve the production of a dormant egg or cyst; rather it involves a transformation of the organism itself into a dormant state through a process called cryptobiosis. “Quiescence is … induced directly by the occurrence of harsh environmental conditions. A quiescent organism can enter this state in many stages of its life, and remains dormant only until the adverse conditions end,” writes Radzikowski.

The All-Female Bdelloid Rotifer

I recently had a chance to study a pond sample in a Petri dish through a friend’s microscope. Attached to a pile of detritus shivering in the current like trees in a gale, were several microscopic rotifers; they were feeding. Their ciliated disk-like mouths twirled madly, capturing plankton to eat. Watching them reminded me of my early research days at Concordia University in Montreal. Probably Philodina (a bdelloid); I had seen many during my stream research in Quebec.

The bdelloid rotifer has dispensed with sexual reproduction entirely and reproduces exclusively by female parthenogenesis. All-female bdelloid rotifers have thrived for forty million years. They’re everywhere, in temporary ponds, moss, even tree bark. Part of the reason for their incredible success lies in their strategy of quiescent dormancy.

In response to unfavourable conditions like a pond drying up, bdelloid rotifers enter a process called anhydrobiosis, contracting into an inert form and losing most of their body water. The bdelloid withdraws her head and foot and contracts her body into a compact shape called a tun; a dormant state that remains permeable to gases and liquids. In this state, bdelloid rotifers can resist ionizing radiation because they can repair DNA double-strand breaks. Early research noted that dormant animals could withstand freezing and thawing from −40°C to 100°C and storage under vacuum. They also tolerated high doses of UV and X radiation. Later work reported that some rotifers could survive extreme abiotic conditions, such as exposure to liquid nitrogen (−196°C) for several weeks or liquid helium (−269°C) for several hours. Dried up adult bdelloid rotifers apparently survived minus 80°C conditions for more than 6 years.

Dormancy is an elegant technique to ride out harsh conditions. The bdelloids can go dormant quickly in any stage of their life cycle—embryo, juvenile or adult—and they’re capable of remaining dormant for decades. They can recover from their dormancy state within hours when the right conditions return and go on reproducing without the need to find a mate.

Research has shown that bdelloid mothers that go through desiccation produce daughters with increased fitness and longevity. In fact, if desiccation doesn’t occur over several generations, the rotifers lose their fitness. They need the unpredictable environment to keep robust. This is partly because they incorporate genes from their environment during anhydrobiosis. When dormant, they acquire mobile DNA and stitch it into themselves through a process called horizontal gene transfer (HGT).

Bdelloid rotifers carry change inside them, through phenotypic plasticity, physiological stress response mechanisms, or life history adaptations. That’s why the bdelloid rotifers survived for millennia and will continue for many more. They are able to keep up with rapid and catastrophic environmental change, not to mention something as gigantic as climate change. They adapt by counting on change.

References:

Munteanu, Nina. 2020. “A Diary in the Age of Water.” Inanna Publications, Toronto. 300pp.

Munteanu, Nina. 2016. “Water Is…The Meaning of Water.” Pixl Press, Vancouver. 586pp.

O’Leary, Denise. 2015. “Horizontal gene transfer: Sorry, Darwin, it’s not your evolution anymore.” Evolution News, August 13, 2015. Online: https://www.evolutionnews.org/201508/horizontal_gene/

Ricci, C. And D. Fontaneto. 2017. “The importance of being a bdelloid: Ecological and evolutionary consequences of dormancy.” Italian Journal of Zoology, 76:3, 240-249.

Robinson, Kelly and Julie Dunning. 2016. “Bacteria and humans have been swapping DNA for millennia”. The Scientist Magazine, October 1, 2016. Online: https://www.the-scientist.com/?articles.view/articleNo/47125/title/Bacteria-and-Humans-Have-Been-Swapping-DNA-for-Millennia/

Weinhold, Bob. 2006. “Epigenetics: the science of change.” Environmental Health Perspectives, 114(3): A160-A167.

Williams, Sarah. 2015. “Humans may harbour more than 100 genes from other organisms”. Science, March 12, 2015. Online: http://www.sciencemag.org/news/2015/03/humans-may-harbor-more-100-genes-other-organisms

Science in Art

Spoiler warning: this post mentions artistic items people are making for sale -- but they're all about science!

This summer I have run into a few people who are inspired by science to make beautiful things. One is a potter looking at living cells through a microscope. One is a graduate student studying Earth Sciences, who inspires kids learning how science and art overlap in this way. And the third is making large pictures showing melting glaciers -- more colourful than you'd think!

Here's a photo I took this summer at the farmer's market in Sooke, BC, where Sydnie Nicole sells her ceramic art. She's studying Art Education, and the surfaces and glazes of her pottery show designs based on the images she sees of living cells through a microscope. Check out her website at this link, where you can see see photos of her work, and her artist's statement which reads in part:

Carved and stamped by hand, Sydnie’s functional and sculptural work reveals a dedication to detail that bridges the disciplines of craft and science into the everyday world.

One particularly charming oval platter is designed to show what a pine needle looks like when you cut a slice across the needle and focus a microscope on the slice. Along with mugs and bowls and plates she makes from clay, Sydnie also has this interesting panel of wall art you can see on the easel behind her, called "Biomedical Artistica." She teamed up with biomedical grad researcher Andrew Agbay for this piece, which shows small spheres delivering medication to the network of living stem cells turning into neurons.

This pair of pottery pieces is a particular favourite of hers -- it's salt and pepper shakers, that sit on her dining table. The nifty part is that the salt cellar is shaped like salt crystals are, in a cube. The pepper shaker is shaped like a black peppercorn, round with wrinkles. Charming!

I found another science artist, but this time online. Jill Pelto is studying for her Masters degree in Earth Sciences at University of Maine. You can check out her Twitter feed at this link, which shows some of her interesting drawings. "I create field sketches of places I have researched, and environmental illustrations," wrote Jill Pelto on her Twitter profile. Y'see, Jill not only makes drawings in the field when she's out gathering data on glaciers and doing research in places as far away as the Falkland Islands, or New Zealand and Antarctica. She makes art based on the jagged lines and curves made when her data is printed in a graph. Sometimes a zigzag line will look to her like a melting glacier, other times it will be part of her drawing of a forest fire. 

Here is an image of her work "Proxies for the Past" which appeared on Yale Climate Connections website. You can read what they wrote about Jill Pelto and her art at this link. To see more of Jill Pelto's art, check out this link to where she sells some of her Glaciogenic Art, including that image.

 

On Twitter, there's a link to images created by students who were inspired by Jill Pelto's art. It's nice to see emerging art as well as her polished pieces.

And if you're a fan of science-inspired art and want to see more, check out the pastel drawings done by Zaria Forman at this link, where she is making a striking series of images based on photographs of glaciers in Antarctica. She makes drawings and paintings using pastels, a chalk-y medium, on large sheets of white paper and large canvases. In the video shown at the link, she is working on a drawing big enough that she is using her fingers to apply the pastels. Melting glaciers means more than just statistics to me when I can see so many shades of blue and white in the ice she draws!

I wrote an illustrated book - about invisible stuff!

By Claire Eamer

Cover art by Marie-Eve Tremblay.
Published by Kids Can Press.

My latest kids' science book - Inside Your Insides: A Guide to the Microbes That Call You Home - hits the bookstore shelves on Tuesday, September 6. And I'm thrilled.

I know, I know - I've been here before. After all, this is my seventh kids' book. But the launch of a new book never loses its charm. There's a long and sometimes painful road from the first exciting bit of research to the finished object - all shiny and glossy and colourful, and just waiting to delight fresh eyes.

This time there's an extra level of delight, at least for me. The topic of the book is the invisible menagerie of tiny critters that make up the human microbiome. The key word here is "invisible." And a key aspect of kids' books is illustration. So, how do you illustrate the invisible?

One solution might have been photographs. Microbes aren't really invisible - just really, really small. You can see some of them through a light microscope and more through an electron microscope, but some are barely visible even with the best equipment. And they....well....they look a bit boring. (Sorry, microbiologists! I know you love them all.)

EHEC bacteria, O104:H4 outbreak strain. Scanning electron microscopy. Bar: 1 µmSource: Gudrun Holland, Michael Laue/RKI

The better solution is an artist - in this case, the marvellous Quebec artist and illustrator Marie-Eve Tremblay.

I should explain that the publisher, Kids Can Press, came up with this solution. I just sent them words and then sat back and crossed my fingers, hoping they'd find a way to bring the book to visual life.

And they certainly did. Marie-Eve's microbes have character, humour, colour, emotion. Not bad for mostly-single-cell organisms. They might not be exactly what a microbiologist sees, but they get some fairly difficult information across in a way that will engage the kids reading the book.

And, who knows? Some of those kids might be the next generation of microbiologists. I hope so!

Thanks, Kids Can Press and Marie-Eve Tremblay, for making my words come to colourful and entertaining life.

If you want to know what reviewers think of the book, check out the reviews in Quill & Quire, School Library Journal, and Kirkus Reviews.

And for some cool information about researching the human microbiome - and keeping your research up to date - see Jan Thornhill's Sci/Why post from March of this year.

My Stinky Sneakers

    Ewww...What is that smell? Were my socks washed in skunk juice? Did my feet turn into moldy cheese I don’t think so. It is my stinky sneakers.

I hold my nose when I take off my sneakers. My mom holds her nose too. My dog sniffs and quivers with delight. Why are my sneakers so smelly?

My stinky sneakers were not dropped in the garbage. They did not come from a manure factory. My sneakers stink because they have tiny creatures called bacteria (back-teer-ee-ah) living in them. It is not the sneakers that smell, it is the bacteria living in them. More precisely, it is not the bacteria in my sneakers that smell, it is their farts.

Your old shoes probably have smelly bacteria too.  But no matter how hard you or I look in our shoes, we will not see the bacteria. They are too small. We cannot see everything that is real.

Bacteria don’t just live in my sneakers… They live all over me, all over my body, inside and out. Bacteria live everywhere. On animals, on plants, in the air, in the soil, in the water. Bacteria live deep in the ground, on the ocean floor, on the top of Mount Everest, in the clouds, in the Antarctic ice.

The bacteria that live on my body are body bacteria. They like it warm, the temperature of me. Not all bacteria living on me are stinky. Some of them keep me healthy. I need them to help me make vitamins and keep my skin clean. But a few of the bacteria that live on my body can make me sick. Sometimes, my throat gets sore because too many bacteria are growing in my mouth.

Most bacteria just hang around, living on me like I live on the Earth. The stinky bacteria living in my sneakers are like that. There is more than one kind of bacteria living in my stinky sneakers. They have big names like Staphylococcus (Staff – ee – low –cock – us) and Propionibacteria (Pro – pee – on –ee – back – teer – ee – a). Stahylococcus are very small, and are shaped like a marble. Propionibacteria are shaped like jellybeans. These kinds of bacteria like to live where it is warm and dark. My sneakers are a perfect home.

My sneakers have something else that these bacteria love..lots of sweat to eat. Feet make a lot of sweat. Most people’s feet make more than a cup of sweat, every day. The sweat my feet makes soaks into my socks and into my sneakers. Sweat is mostly water, but there is also a little bit of salt and a little bit of sugar. Sneaker bacteria eat this salt and this sugar. It is their favorite food.

The more sweat in my sneakers, the more bacteria food. The bacteria grow and make even more bacteria. If there was a straight line of bacteria from my toe to my heel, there would be sixty thousand bacteria in a row. Lots of sweat makes crowds of bacteria. My sneakers are like a giant bacteria concert, like the Superbowl, or Times Square on New Year’s Eve.

My sweat does not smell. But when the bacteria in my stinky sneakers eat it, they sure leave behind smells when they finish dinner. In a way, it is like lots of minuscule bacteria farts. Phew!

Scientists are trying to grow a new kind of bacteria that eats sweat but does not make bad smells. This kind of bacteria would live in sneakers and clothes and eat up all the sweat and dirt. My sneakers would stay clean and never need to be washed. My mom says these scientists should hurry up.

Stinky sneakers mean that I have been playing and running. Stinky sneakers mean that I have been exercising and staying healthy. Stinky sneakers give my bacteria a place to live and food to eat.

When I get home, I take my stinky sneakers off. And I put my smelly socks in the laundry basket. And then I do the stink test.  I lift my leg in the air, point my toes at my sister and say, “smell my feet.” If she holds her nose or runs away, my feet are stinky too. And then I know…

...it is time to take a bath.