How the Bdelloid Rotifer Lived for Millennia — Without Sex

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.

Filamentous algae collected in Lake Ontario, ON (photo by Nina Munteanu)

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…

Sketch of common zooplankton and phytoplankton (illustration by Nina Munteanu)

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 in a wink. And like the thief in the night, they pose a harsh and uncertain home to many small organisms. These environments are ever-changing, unstable, chaotic and unpredictable. Yet, anyone who has studied these variable ecosystems understands that they team with life. 

When a puddle or ephemeral pond dries up then reappears with rain, how can these communities thrive? Or 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.

Philodina, a bdelloid rotifer (microscope photo by Bob Blaylock)

Animalcules & the Bdelloid Rotifer

In 1701, Antonie van Leeuwenhoek observed that “animalcules” (likely the bdelloid rotifer Philodina roseaola) survived desiccation 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. (on right: sketch of bdelloid rotifer by Nina Munteanu

Bdelloid rotifers can go into quiescent dormancy at practically any stage in their life cycle in response to unfavorable conditions. 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. Desiccated adult bdelloid rotifers apparently survived minus 80°C conditions for more than 6 years. The dormant eggs of cladocerans and ostracods also survived below freezing temperatures for years.

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, living inside tubes or gelatinous holdfasts and may even be colonial. Rotifers reproduce by parthenogenesis (in the absence of mates), producing clones (like cladocerans). Resting eggs (sometimes called zygotes) survive when a pond dries up. Bdelloid rotifers don’t produce resting eggs; they survive desiccation through a process called anhydrobiosis, contracting into an inert form and losing most of their body water. Embryos, juveniles and adults can undergo this process. The bdelloid withdraws its head and food and contracts its body into a compact shape called a tun; a generally unprotected dormant state that remains permeable to gases and liquids. Like Tardigrades (see below), Bdelloid rotifers can resist ionizing radiation because they can repair DNA double-strand breaks.

The long-term survival and evolutionary success of bdelloid rotifers in the absence of sex arises from horizontal gene transfer via DNA repair.

In my eco-novel A Diary in the Age of Water the limnologist Lynna visits her technician Daniel as he peers through a microscope and makes the observation of why the bdelloid rotifer is well-suited to climate change:

I bent to peer through the eyepiece at what turned out to be a pond sample in a Petri dish. Attached to a pile of detritus shivering in the current, several microscopic metazoans—rotifers—swung like trees in a gale; they were feeding. Their ciliated disk-like mouths twirled madly, capturing plankton to eat. Watching them reminded me of my early research days as an honours undergrad at Concordia University in Montreal. Probably Philodina, I thought; I had seen many during my stream research in Quebec.

“They’re the future,” Daniel said, looking up at me with a smirk as I straightened.

I raised my eyebrows, inviting him to elaborate, which he cheerfully did.

“They’re the future because of their incredible evolutionary success and their ecological attraction to environmental disaster.” He knew he’d piqued my interest. “These little creatures have existed for over forty million years, Lynna. Without sex! And they’re everywhere. In temporary ponds, moss, even tree bark. 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.” They incorporate genes from their environment: they acquire DNA transposons—mobile DNA—through HGT.”


The bdelloid all-female populations have thrived for millions of years by maintaining a robust and diverse population through epigenetics and DNA repair during dormancy…The dormancy of all-female bdelloids is an elegant technique to ride out harsh conditions. The bdelloids can go dormant quickly in any stage of their life cycle, 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.

Highly variable environments tend to support rare species: organisms that are uniquely equipped for change. These are the explorers, misfits, and revolutionaries who do their work to usher in a new paradigm. They carry change inside them, through phenotypic plasticity, physiological stress response mechanisms, or life history adaptations. Like bdelloid rotifers going dormant through anhydrobiosis. Or blue-green algae forming dormant akinete spores. In tune with the vacillations of Nature, epigenetics-induced adaptation is the only option for keeping up with rapid and catastrophic environmental change, not to mention something as gigantic as climate change. That’s why the bdelloid rotifers survived for millennia and will continue for many more. They adapt by counting on change.

Maple swamp forest in Trent Nature Sanctuary, ON (photo and rendition by Nina Munteanu)


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:

Ricci, C. And D. Fontaneto. 2017. “The importance of being a bdelloid: Ecological and evolutionary consequences of dormancy.” Italian Journal ofZoology, 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:

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:

Nina Munteanu is a Canadian ecologist / limnologist and novelist. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit for the latest on her books. Nina’s bilingual “La natura dell’acqua / The Way of Water” was published by Mincione Edizioni in Rome. Her non-fiction book “Water Is…” by Pixl Press (Vancouver) was selected by Margaret Atwood in the New York Times ‘Year in Reading’ and was chosen as the 2017 Summer Read by Water Canada. Her novel “A Diary in the Age of Water” was released by Inanna Publications (Toronto) in June 2020.

Darwin’s Paradox Revisited: Compassion and Evolution

In 2007, when I started my first blog, The Alien Next Door, I wrote an article that explored the term “Darwin’s Paradox”—it’s not just the title of my science fiction thriller Darwin’s Paradox released that year by Dragon Moon Press—but  a term coined by scientists to describe the paradoxical phenomenon exhibited by coral reefs.

Defying The Laws of Thermodynamics

Darwin described coral reefs as oases in the desert of the ocean. Coral reefs comprise one of the richest ecosystems on Earth, in apparent violation of the laws of thermodynamics (high productivity in a low-productivity environment). Productivity ranges from 50 to 250 times more than the surrounding ocean. How do they thrive in crystal-clear water, largely devoid of nutrients? Part of the answer lies in the coral’s efficiency in recycling nutrients like nitrate and phosphate.

First, the rough coral surface amplifies water turbulence at a microscopic level, disrupting the boundary layer that usually settles on objects under water and lets the coral “hoover” up the sparse nutrients. I stumbled upon a similar phenomenon during my grad work on temperate streams and published my serendipitous discovery in the journal Hydrobiologia. I was researching how periphyton (attached “algae”) colonized submerged glass slides and observed that the community preferred the edges of the slides because the micro-turbulence there provided more opportunity for attachment and nutrition.

Second, lots of corals also function symbiotically with specialized algae (called zooxanthelae), which provide the coral with food (through photosynthesis) and, in turn, get food from the wastes created by the coral.  

Can the science of symbiosis teach us something about another Darwin’s Paradox?

The Evolution of Compassion

In a September 2013 article in the Jewish World Review, Boston Globe reporter Jeff Jacobywrote:

“Charles Darwin struggled with a paradox: If evolution is a struggle for survival, how could generosity, compassion, and other altruistic virtues have spread through natural selection? Darwin could see the clear evolutionary benefit to groups that inculcated ethical values in their members. Imagine two competing primitive tribes, equally matched — except that ‘one tribe included a great number of courageous, sympathetic, and faithful members, who were always ready to warn each other of danger, [and] to aid and defend each other.’ (Darwin, “The Descent of Man”). There was little doubt that tribes highly endowed with such virtues ‘would spread and be victorious over other tribes.’”

“How did any tribe evolve such ethical qualities in the first place?” asks Jacoby. Brave individuals who risked their lives for others “would on average perish in larger numbers than other men.” It hardly seemed possible, Darwin conceded, that, “such virtues … could be increased through natural selection, that is, by the survival of the fittest.” So, how did it and why?

Jacoby quotes Sir Jonathan Sacks, Britain’s Orthodox chief rabbi, who pointed to “the central drama of civilization: Biological evolution favors individuals,” says Sacks. “But cultural evolution favors groups.… Selfishness benefits individuals [only in the short-term and only in a limited way—my comment], but it is [ultimately] disastrous to groups, and it is only as members of a group that individuals can survive at all.”

Jacoby describes the vast literature in evolutionary psychology and sociobiology that have demonstrated humanity’s hard-wired moral capacity. “We are born with an aptitude for empathy and fairness,” said Jacoby, citing recent neurological experiments that have demonstrated that an act of generosity triggers a pleasurable response in the brain.

Abraham Lincoln summarized it in seven words: “When I do good, I feel good.”  Psychologists call it the “helper’s high”. Neuroscientists and behavioral scientists are demonstrating unequivocally the benefits of altruism to our health and happiness. Scientists have designed experiments that actually trace altruism—and the pleasure we gain from it—to specific regions and systems in the brain. Key studies now provide striking evidence that our brains are wired for altruism. 

The Social Brain and the Seat of Compassion  

In a study published in the Proceedings of the National Academy of Sciences (Moll et al, 2006), a team of neuroscientists lead by Dr. Jordan Grafman, reported that, “when people made the decision to donate to what they felt was a worthy organization, parts of the midbrain lit up—the same region that controls cravings for food and sex.” The brain experiences a pleasurable response when we engage in good deeds that benefit others. 

Dr. Grafman found that the subgenual area in the frontal lobe near the midpoint of the brain was also strongly active when his study subjects made the decision to give to charity. The area houses many receptors for oxytocin, a hormone that promotes social bonding. “The finding suggests that altruism and social relationships are intimately connected—in part, it may be our reliance on the benefits of strong interpersonal connections that motivates us to behave unselfishly,” reports Elizabeth Svoboda in the WallStreet Journal. The team also found that the nucleus accumbens, which contains neurons that release the pleasure chemical dopamine, was triggered when a person chose to help another.

A 2007 study headed by neuroscientist Scott Huettel and reported in Nature Neuroscience(Tankersley, et al., 2007) connects altruism to the posterior superior temporal cortex (pSTC), an area in the upper rear of the brain that lets us perceive goal-directed actions by someone or something else. Results suggest that altruism depends on, and may have evolved from, the brain’s ability to perform the low-level perceptual task of attributing meaning and motive in the actions of others.

“Our findings are consistent with a theory that some aspects of altruism arose out of a system for perceiving the intentions and goals of others,” said Dr. Huettel. “To be altruistic, you need to see that the people you’re helping have goals, and that your actions will have consequences for them.” 

Research led by Michael Platt reported in Nature Neurosciencein 2012, showed that the anterior cingulate gyrus(ACCg) is an important nexus for the computation of shared experience and social reward. That same year researchers at Mount Sinai School of Medicine in New York published research in the journal Brainthat suggested that the anterior insular cortexis the activity centre of human empathy.

I find it both interesting and exciting that these studies link different brain regions to altruistic and compassionate behavior. “There are certain to be multiple mechanism that contribute to altruism, both in individuals and over evolutionary time,” added Huettel. This is the nature of the brain, whether we look at intelligence, motivation or physical characteristics. And I am convinced that we will someday find that many other areas—if not the entire area—of the brain are involved. Moreover, researchers have shown that engaging—or even witnessing—generous acts can reduce stress, increase immunity (e.g., increased antibody levels), and longevity.

Emiliana Simon-Thomas, science director for the Greater Good Science Center at the University of California, Berkeley, explains the chemical activity that happens in our heads when we commit acts of altruism. “There are multiple reward systems that have been tied to pleasurable feelings when people help others or contribute to the well being of the people around them,” she notes. These reward systems are comprised of three main chemicals that are released when we commit an act of kindness and feel pleasure: Dopamine, Oxytocin and Serotonin. According to Simon-Thomas, Dopamine is most closely related to hedonic pleasure — or pleasure derived from self; oxytocin is tied to more social pleasure — especially with regard to physical contact; and serotonin is implicated in a more broad mood state. “All three of these, again, are sort of intersecting and interacting, and depending on the context that you’re in, represent feelings of pleasure in different context,” she explains. “All these systems are activating and parallel, and sort of influencing one another as you go through life.” So when I do a good deed, I am rewarding myself with a cocktail of wonder drugs that please me and make me smile.

So, what I’ve known since I was a child is now proven: doing good deeds is mutually beneficial to the giver and the receiver.

Path through winter forest in the fog, ON (photo by Nina Munteanu)

Altruism in All Beings

The notion that all aspects of life on this planet—not just humanity—have the capacity to act altruistically remains controversial—even among professional scientists and researchers. We are not unique in experiencing or practicing altruism, in acting altruistically and benefiting from our own altruistic acts. It is however a matter of perspective, bias and open-mindedness. Many examples of altruistic behavior and empathy exist in the rest of the living world on our planet.

Nature’s Heroes

Scientists have been demonstrating for years that cooperation among organisms and communities and the act of pure altruism (not reciprocal altruism or kin/group selection) is, in fact, more common in Nature than most of us realize. Valid examples of true altruism in the wild in many species exist. The key here is “in the wild”—not in captivity, where inherent behavior is often modified (see my Alien Next Door article “The SamaritanParadox Revisited: The Karma Ran Over the Dogma”).

Despite the overwhelming evidence for altruism in every aspect of our world, some researchers continue to design experiments and then draw sweeping conclusions based on animals in captivity to suggest that only humanity possesses the ability to behave altruistically—and then again only by social-instruction (aka “the Selfish Gene” of Richard Dawkins vs. the “Social Gene” of Lynn Margulis).

Examples of altruism abound and range among mammals, birds, invertebrates and even Protista. Some examples include: dogs, cats, ducks, squirrels, wolves, mongooses, Meer cats, baboons, chimpanzees, vampire bats, dolphins, walruses, lemurs, African buffalo—to name a few.

de Waal explained that “evolution favors animals that assist each other if by doing so they achieve long-term benefits of greater value than the benefits derived from going it alone and competing with others” (de Waal 2006). The prevalent phenomenon of altruism is Nature’s answer to the Prisoner’s Dilemma. “Empathy evolved in animals as the main … mechanism for [individually] directed altruism,” said deWaal. And it is empathy—not self-interest—that “causes altruism to be dispensed in accordance with predictions from kin selection and reciprocal altruism theory.” deWaal further proposed that the scientific community has become polarized between evolutionary biologists on the one side, and, on the other, a discrete group of economists and anthropologists that “has invested heavily in the idea of strong reciprocity,” which demands discontinuity between humans and all other animals.

“One of the most striking consequences of the study of animal behavior,” says anthropologist Robert Sapolsky, “is the rethinking … of what it is to be human.” He notes that, “a number of realms, traditionally thought to define our humanity, have now been shown to be shared, at least partially, with nonhuman species.” (Sapolsky 2006). This makes some of us uncomfortable. To some, it threatens to make us less special. The corollary is that this demonstrates that we possess intrinsic virtue, not something “painted” on through cultural teaching or diligent personal effort. Of course, it also means that all other beings possess intrinsic value too. In the final analysis, what we generally “know” is colored by what we believe and want to continue believing.

First big snow in Thompson Creek marsh, ON (photo and dry brush rendition by Nina Munteanu)

Universal Altruism and Gaia

What does all this mean? Does the very existence of altruism demonstrate the connectivity of all life on Earth? Let’s not stop there. Does the grace of altruism reflect a fractal cosmos imbued with meaning and intent? Was it the grace of altruism that allowed it all to happen in the first place? Don’t we all come from grace?

Despite struggles with acceptance for some of us, we are emerging enlightened to the fractal existence of grace and altruism embedded in the very nature and intentions of our universe.

I come full circle to my book Darwin’s Paradox, a tale of fractal intelligence and universal cooperation. A tale of emerging awareness of Self and Other as One…Evolution through cooperation… Creative DNA…Manifestation through thought and intent…Self-organization and synchronicity…A hero’s journey…and coming Home…

In this season of gratitude, we celebrate altruism in giving and in receiving graciously.

Merry Christmas!

First snow over Thompson Creek outlet, ON (photo by Nina Munteanu)

Links / Books of Interest: 2011. “Altruism: the Helper’s High”.

Atwood, Margaret. 2009. “Dept: Not Just A Four Letter Word”. Zoomer. March, 2009 (

Centre for Compassion and Altruism Research and Education, Stanford School of Medicine:

Jacoby, Jeff. 2013. “Darwin’s conundrum: Where does compassion come from?”

Ridley, Matt. 1998. The Origins of Virtue: Human Instincts and the Evolution of Cooperation. Penguin Books, 304pp.

Svoboda, Elizabeth. August 31, 2013. “Hard-Wired for Giving” in The Wall Street Journal;

Svoboda, Elizabeth. 2013. “What Makes a Hero? The Surprising Science of Selflessness” Current. 240 pp.

Munteanu, Nina. Aug, 2010. “The Samaritan Paradox Revisited: The Karma Ran Over the Dogma” in The Alien Next Door;

Munteanu, Nina. June, 2010. “What Altruism in Animals can Teach Us About Ourselves” in The Alien Next Door; 

Munteanu, Nina. March, 2010. “Gaia versus Medea: A Case for Altruism” in The Alien Next Door;

Munteanu, Nina. Feb, 2009. “Margaret Atwood’s Wise Words About Dept & Altruism…A Portrait of the Artist as a Real Hero” in The Alien Next Door;

Munteanu, Nina. August, 2007. “Is James Bond an Altruist?—Part 2” in The Alien Next Door;

Nina Munteanu. August, 2007. “Co-evolution: Cooperation & Agressive Symbiosis” in The Alien Next Door;

Nina Munteanu. July, 2007. “Altruism at the Heart of True Happiness” in The Alien Next Door;

Ridley, Matt. 1998. “The Origins of Virtue: Human Instincts and the Evolution of Cooperation.” Penguin Books. 304 pp.

References for Altruism in All Animals:

Bradley, Brenda. 1999. “Levels of Selection, Altruism, and Primate Behavior.” The Quarterly Review of Biology, 74(2):171-194.

De Waal, Frans, with Robert Wright, Christine Korsgaard, Philip Kitcher, and Peter Singer. 2006. “Primates and Philosophers: How Morality Evolved”. Princeton: Princeton University Press.

Goodall, Jane. 1990 Through A Window: My Thirty Years with the Chimpanzees of Gombe. Boston: Houghton Mifflin.

Moll, Jorge, Frank Krueger, Roland Zahn, Matteo Pardini, Ricardo de Oliveira-Souza, and Jordan Grafman. 2006. “Human fronto-mesolimbic networks guide decisions about charitable donation.” In: Proc. Natl. Acad. Sci., USA, 103(42): 15623-15628.

Sapolsky, Robert M. 2006. “Social Cultures Among Nonhuman Primates.” Current Anthropology, 47(4):641-656.

Svoboda, Elizabeth. 2013. “What Makes a Hero? The Surprising Science of Selfishness.” Current.

Tankersley D et al.  2007. “Altruism is Associated with an Increased Response to Agency.”  Nature Neuroscience, February 2007, Vol. 10(2), pp. 150-151.

Warneken, F. & Tomasello, M. 2006. “Altruistic Helping In Human Infants and Young Chimpanzees.” Science, 311, 1301–1303.

Warneken, F., Hare, B., Melis, A. P., Hanus, D. & Tomasello, M. 2007. “Spontaneous Altruism By Chimpanzees and Young Children.” PloS Biology, 5(7), e184.

de Waal, F. B. M. 2008. “Putting the Altruism Back Into Altruism: The Evolution of Empathy.” Annu. Rev. Psychol., 59, 279–300.

de Waal, F. B. M., Leimgruber, K. & Greenberg, A. R. 2008. “Giving Is Self-rewarding for Monkeys.” Proc. Natl. Acad. Sci., USA, 105, 13685–13689.

Nina Munteanu is a Canadian ecologist / limnologist and novelist. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit for the latest on her books. Nina’s bilingual “La natura dell’acqua / The Way of Water” was published by Mincione Edizioni in Rome. Her non-fiction book “Water Is…” by Pixl Press(Vancouver) was selected by Margaret Atwood in the New York Times ‘Year in Reading’ and was chosen as the 2017 Summer Read by Water Canada. Her novel “A Diary in the Age of Water” was released by Inanna Publications (Toronto) in June 2020.