This is where the interaction of biology and physics gets mysterious — just as the shark finds its dinner interrupted by a cloud of protective slime that appeared out of nowhere around an otherwise placid hagfish.

Jean-Luc Thiffeault, a University of Wisconsin-Madison math professor, and collaborators Randy Ewoldt and Gaurav Chaudhary of the University of Illinois have modeled the hagfish’s gag-inducing defense mechanism mathematically, publishing their work today in the Journal of the Royal Society Interface.

The ocean-dwelling hagfish is unique for all the strangest reasons. It has a skull, but no spine or jaw. Its skin hangs loose on its

body, attached only along the back. Its teeth and fins are primitive, underdeveloped structures best described with qualifiers — “tooth-like” and “fin-like.”

But it has an amazing trick up that creepy, loose sleeve of skin: In the blink of an eye (or flash of attacking tail and teeth) the hagfish can produce many times its own body’s volume in slime. The goop is so thick and fibrous, predators have little choice but to spit out the hagfish and try to clear their mouths. “The mouth of the shark is immediately chock full of this gel,” Thiffeault says. “In fact, it often kills them, because it clogs their gills.”

The gel is a tangled network of microscopic, seawater-trapping threads unspooled from balls of the stuff ejected from glands along the hagfish’s skin. These “skeins” are just 100 millionths of a meter in diameter (twice the width of a human hair), but so densely coiled that they can contain as much as 15 centimeters of thread. Curious scientists have looked at the unraveling before, putting the skeins in salt water to see how long it took them to come apart.

“The hagfish does it in less than half a second, but it took hours of soaking for the threads to loosen up in experiments,” says Thiffeault, whose research is focused on fluid dynamics and mixing. “Until they stirred the water, and it happened faster. The stirring was the thing.”

The slime modelers set out to see if math could tell them whether the forces of the turbulent water of a bite-and-shake attack were enough to unspool the skeins and make the slime, or if another mechanism — like a chemical reaction providing some pop to the skein — was required.

Ewoldt, a mechanical engineering professor, and his graduate student Chaudhary began unraveling skeins under microscopes, watching the process as loose ends of thread stuck to the tip of a moving syringe and trailing lengths spun out from the ball.

“Our model hinges on an idea of a small piece that’s initially dangling out, and then a piece that’s being pulled away,” says Thiffeault. “Think of it as a roll of tape. To start pulling tape from a new roll, you may have to hunt for the end and pick it loose with your fingernail. But if there’s already a free end, it’s easy to catch it with something and get going.”

Unrolling requires a big enough difference between the drag on the free end and an opposing push on the skein — a ratio larger than a tipping point the researchers refer to informally as the “peeling number” — to free more thread.

“That’s unlikely to happen if the whole thing is moving freely in water,” says Thiffeault. “The main conclusion of our model is we think the mechanism relies on the threads getting caught on something else — other threads, all the surfaces on the inside of a predator’s mouth, pretty much anything — and it’s from there it can really be explosive.”

It doesn’t even have to be a single snag.

“Biology being the way it is, it doesn’t have to be exact. Things get to be messy,” says Thiffeault. “That leading bit of thread can get caught a little bit, then slip, then get caught again. As long as it’s happening to enough skeins, it’s pretty fast that you’re in the slime.”

The skeins may get a boost from mucins, proteins found in mucus that could speed the breakup of packed thread, “but those kinds of things would just help the hydrodynamics,” says Thiffeault, who once calculated the extent to which swimming marine life mix entire oceans with their fins and flippers.

“It’s just hard to imagine there’s another process other than hydrodynamic flow that can lead to these timescales, that burst of slime,” he says. “When the shark bites down, that does create turbulence. That creates faster flows, the sorts of things that provide the seed for these things to happen. Nothing is going to happen as nicely as in our model — which is more of a good start for anyone who wants to take more measurements — but our model shows the physical forces play the biggest role.”

The hydrodynamics of hagfish slime is not just a curiosity. Understanding the formation and behavior of gels is a standing issue in many biological processes and similar industrial and medical applications.”

One of the things we’d love to work on in the future is the network of threads. I love thinking about modeling materials as big random collections of threads,” Thiffeault says. “A simple model of entangled threads may help us see how that network determines the macroscopic properties of a lot of different, interesting materials.”

A grant from the National Science Foundation (CBET-1342408) helped support this research.

But the toxins produced in cyanobacteria blooms may also have protective effects on sand-grain-sized lake animals that ingest them, much as the toxins in milkweed plants protect monarch butterflies from parasites, according to a new study from University of Michigan ecologists.

The laboratory-based study shows that tiny, shrimp-like freshwater crustaceans called Daphnia can gain protection from fungal parasites by consuming toxins produced by bloom-forming cyanobacteria. Commonly known as water fleas, Daphnia play a key role in freshwater food webs and are a vital food source for many fish.

The U-M researchers plan follow-up studies to see if the protective effects they observed in the lab are also occurring in lakes. They’ll also explore the potential of developing anti-fungal drugs for human use.

The study is scheduled for publication Jan. 15 in the journal Proceedings of the Royal Society B. The first author is Kristel Sánchez, who did the work for her master’s thesis in the U-M Department of Ecology and Evolutionary Biology. Co-authors include her faculty advisers, U-M ecologists Mark Hunter and Meghan Duffy.

“This paper shows that Daphnia living in Michigan lakes can gain protection from fungal parasites through the toxins that are present in bloom-forming cyanobacteria,” said Hunter, who has studied monarchs at U-M’s Biological Station for more than a decade.

“This is an amazing aquatic parallel of the monarch butterflies, which gain protection from their parasites from the toxins in milkweed. It suggests that animal medication may be even more common than we thought, extending into the aquatic realm.”

It’s been known for decades that animals such as chimpanzees seek out medicinal herbs to treat their diseases. In recent years, the list of animal pharmacists has grown much longer, and it now appears that the practice of animal “self-medication” is a lot more widespread than scientists had previously known.

But most studies of animal self-medication have focused on terrestrial ecosystems. Relatively little is known about how an animal’s diet serves as sources of medications in aquatic systems.

To be clear, the current study does not show that Daphnia are self-medicating in the wild. To demonstrate self-medication, researchers would have to show that Daphnia feed preferentially on toxin-producing cyanobacteria and algae to reduce their disease risk. The researchers will look for evidence of this type of selective foraging in the next phase of the study.

But the current study does provide strong evidence for the protective properties of plant toxins consumed by Daphnia.

“Fungal pathogens have devastating impacts on crops, wildlife, and even people,” Duffy said. “To me, the idea that compounds for fighting those might be just below the surface of our local lakes is really exciting.”

Sánchez raised Daphnia dentifera, a common herbivore in North American lakes, in the laboratory and fed individuals one of eight species of green algae or cyanobacteria (formerly known as blue-green algae). In the wild, Daphnia feed on algae and bacteria floating in the water column; they are part of a group of tiny aquatic animals known as zooplankton grazers.

Five species of green algae and three species of cyanobacteria were used, and they differed in their nutritional value and toxin production. Green algae tend to be more nutritious for Daphnia than toxin-producing cyanobacteria.

Cyanobacteria used in the study included one species of Microcystis, a group of common colony-forming cyanobacteria largely to blame for Lake Erie’s annual summer blooms. Some Microcystis species produce liver toxins called microcystins. In her experiment, Sánchez added pure microcystin to some of the Microcystis cultures to approximate levels of the toxin commonly observed during cyanobacteria blooms.

The lab-reared Daphnia in the U-M study were then exposed to one common fungal parasite and one common bacterial parasite. In the wild, Daphnia become infected by consuming parasite spores in the water.

The researchers found that diet had striking effects on the infection prevalence of the fungal parasite, but not the bacterial parasite.

Two of the cyanobacteria diets — including the diet treatment in which pure microcystin was added to beakers containing Microcystis cultures — completely prevented fungal infections. The diet of Microcystis alone, without additional microcystin, resulted in very low levels of fungal infection.

Fungal infections were also completely prevented when Daphnia fed on the green alga Chlorella. In all, four of the nine dietary treatments showed strong evidence of anti-fungal activity.

“I thought I would probably get one diet out of the nine that showed some medicinal effect,” Sánchez said. “The fact that nearly half of the diet treatments showed some sort of medicinal effect was really surprising and suggests that we are not paying enough attention to the mechanism of self-medication in aquatic ecosystems.”

In contrast, none of the diet treatments prevented infection with the bacterial parasite. Also, uninfected Daphnia that consumed a diet of green algae produced two- to three-fold more offspring than those that ate cyanobacteria, confirming the higher nutritional quality of the green algal diets. And, in general, growth was reduced by parasite infection.

Sánchez plans to continue the work for her doctoral research project, with Duffy as her adviser. The researchers will look for evidence of self-medication and will further examine the anti-microbial properties of the three toxins that showed fungal-fighting activity in the initial study: microcystin-LR, anatoxin-a, and chlorellin. Researchers from Minnesota and Georgia will join the project.

“A lot of natural products research is done by screening tons of plant or algal material and using different bioassays and hoping you get lucky and find a new compound or something that is active,” Sánchez said. “But why not look at what is happening already in nature? I think this is what really appealed to me and why I chose to work on this project.”

The work has broad ecological implications, the researchers say, in part because a warming global climate is expected to increase the frequency of cyanobacteria blooms in some regions. That change could alter disease dynamics among Daphnia, which in turn “could have important consequences for lake food webs, as Daphnia are key grazers and disease outbreaks within Daphnia populations can influence ecosystem-level processes,” the authors wrote.

Based on snakebite documentation from Mojave rattlesnakes as far back as the 1920s, it was thought that these feared pit vipers only had neurotoxic venom, a cocktail of enzymes and peptides that disrupts neurons and paralyzes the nervous system. However, a few cases were curiously different, with patients displaying symptoms such as tissue damage, disorientation and difficulty clotting blood. After several decades of inquiry, scientists later credited these symptoms to a second venom type in the Mojave rattlesnake: hemorrhagic, which acts by destroying tissues in the body.

To discover which venom type occurs where, herpetologists — the amphibian-and-reptile-loving scientists — have been collecting data on Mojave rattlesnakes in the Southwest. However, it wasn’t until a recent publication by Clemson College of Science postdoctoral researcher Jason Strickland and professor of biological sciences Christopher Parkinson that the extent of the distribution was better understood. Their findings show a peculiar variability in the species.

“Prior to this paper, the ‘herp’ community thought that hemorrhagic venom was really rare and was only in one location in Arizona and one location in Mexico, but we show that it’s found in several places throughout the snake’s distribution,” Strickland said. “There were a few instances when individuals in our sample had both types of venom, which our data suggest are hybrids.”

This preservation of multiple venom types within one species defies science’s expectations. The principles of natural selection — “survival of the fittest” as it’s colloquially known — would predict that one of the venom types would fix and the other would slowly diminish over the course of several generations. The venom that wins out is dependent on which type — hemorrhagic or neurotoxic — best suits the Mojave rattlesnake as it hunts for prey in the arid desert. Yet this is not what’s happening.

The finding is made more peculiar by the results of a summer 2018 study that discovered four genetically distinct lineages of the Mojave rattlesnakes throughout the southwestern U.S. and central Mexico along with evidence that the lineages are breeding with one another. Diving deeper into natural selection, this swapping of genes among Mojave rattlesnakes should have reduced the genetic diversity between their lineages, effectively homogenizing venom types until the fittest rules.

“From an evolutionary standpoint, this is abnormal. This is not what you’d expect,” Strickland said. “Gene flow should prevent this much variation. But even with the amount of gene flow we find in these populations, the selection is strong enough to maintain these specific venom types in a very local environment.”

“What we’ve been able to show is that there are local optima. In Texas, the neurotoxic venom type seems to be the optimum for this species. But if we go south into Mexico or over near Phoenix, something in nature is changing, where the local optimum requires a different venom type,” said Parkinson, who holds a joint appointment at Clemson University in College of Agriculture, Forestry and Life Science’s forestry and environmental conservation department.

The public’s role in the scientific process

The discovery required a large research collaboration between the principal investigators and students in five labs across the U.S. and Mexico, in addition to almost 100 citizen-scientists whom Strickland and colleagues assembled through social media and networking. In sum, the researchers collected 216 Mojave rattlesnakes for their study in California, Arizona, New Mexico, Texas and Mexico. The “herp” community, it turns out, is a strong one, with everyday snake enthusiasts eager to help researchers for the betterment of the snake species.

The team met some of those “herpers” at an annual west Texas conference called SnakeDays — directed by enthusiast Jeff Adams — that unites citizens who are interested in reptiles, as well as academics, fish and wildlife law enforcement and “herp” photographers to celebrate and raise money for wildlife diversity conservation.

“By relying on the people at SnakeDays, what would have taken Jason and Chris 10-20 years’ time to study was then completed in just a few years,” Adams said. “It’s much more efficient for scientific professionals to rely on citizens outside of their research boundaries, because citizens know more about finding the local flora and fauna. It’s also cost efficient. Citizen science reduces the cost of research projects so that researchers like Jason and Chris can better utilize their funding.”

It’s the citizen science aspect, as well as “the educational aspect of graduate students and postdocs working across borders,” that Parkinson takes away from this study.

“The science is really important, no question, but collaborative research and citizen science are so important to move science forward. It’s not just about some geeky academic sitting in a room anymore, it’s about how the research affects people,” Parkinson said.

A venomous species with clinical importance

Less than 1 percent of the U.S. population is bitten by a venomous snake each year, and even fewer die from their symptoms. For the few unlucky people who are bitten, knowing the Mojave rattlesnake distribution can lead to better treatment outcomes. If doctors know what venom type persists in their region, they can administer the proper treatment more strategically.

“These authors have published the most extensive study of one of the most medically important snakes in North America, delivering provocative novel perspectives and surprising new discoveries,” said Sean Bush, a clinical herpetologist at Eastern Carolina University. “This work provides an understanding of how and why venom varies, which translates clinically into a foundation for anti-venom development, drug choice and the tailored medical management of snakebite.”

For scientists, the team’s study points toward the Mojave rattlesnake as being a fascinating model species for population genetics and evolutionary studies. Whether related to prey, the environment or a dietary shift over the course of development, why is the Mojave rattlesnake challenging science’s predictions? What is the mechanism?

Future research in the Parkinson lab intends to consider these questions through studies of venom evolution in New World snake species.