In the world of micro life, Francesca Leasi’s name looms large

The microscopic animals Dr. Francesca Leasi studies can’t be seen with the naked eye. Yet for all their size, they may hold vital clues to how life adapts to environmental change and what traits allow organisms to survive it.

In early June, Leasi, a UC Foundation associate professor in the University of Tennessee at Chattanooga Department of Biology, Geology and Environmental Science, spent two intense weeks in the Outer Banks—a series of barrier islands off the coast of North Carolina—searching for answers hidden beneath the surface of saltwater.

Accompanied in the field by UTC students Sebastian Jimenez and Jasmine Castellano and external collaborator Diego Fontaneto of the National Research Council of Italy, Leasi was investigating how tiny aquatic creatures, known as monogonont rotifers, survive dramatic shifts in salinity.

The research is supported by a four-year, $696,680 grant awarded to Leasi from the National Science Foundation in 2024.

“We are fortunate that Dr. Leasi is engaging our students in this exciting research,” said BGE Department Head and UC Foundation Professor Gretchen Potts. “Her students are gaining valuable experience in the field and the lab.”

Monogonont rotifers are crucial to ecosystem health, Leasi explained. They help break down organic material and serve as a food source for larger organisms.

“I’m very passionate about these small animals,” Leasi said. “They are very important and there is an entire world to discover and to describe.”

Leasi, who joined UTC in 2018, said the scope of the current fieldwork is to explore the biodiversity of these microscopic animals in the saltwater habitats along the western Atlantic coast from North Carolina to Florida—a previously understudied region.

“We began the field work in Miami back in February,” she said, “and this time we went to North Carolina, where the field work was more extensive, much longer and more intense.”

During this trip, the team collected water, algae and sediment samples near Roanoke Island, where they were based at East Carolina University’s Coastal Studies Institute. She said the location was selected for its wide range of salinity gradients, a key condition in rotifer habitats.

“We collected the samples by following a protocol that includes more traditional taxonomy, looking at animals under the microscope and identifying animals by morphology,” she explained. “But we also collected the samples for biomonitoring using molecular techniques.”

Leasi said the group spent long days extracting individual organisms.

“We took the animals one by one. We placed the animals on a slide. We took photos and videos. Then we put each animal into a tube for DNA analysis,” she said. “We used a combination of morphology and DNA barcoding to investigate what’s in there.”

The results, she said, were incredible. At least 300 specimens were sorted, with 30 different species identified, and “we think at least three or four are potentially new to science.”

Their size? None of the organisms are visible to the naked eye.

“They are less than half a millimeter,” Leasi said. “They are in the order of microns. It takes a thousand microns to make a millimeter.”

But under the microscope, a surprising level of complexity emerged. Despite their scale, she explained that these animals are fully formed, complete with brains, stomachs and—in some cases—appendages.

“You see complete animals that are of very different magnitudes in terms of size,” she said. “They are capable of withstanding very different ecological conditions.”

One of her favorite moments came when she observed a group of marine water bears—also known as tardigrades—clinging to grains of sand with tiny suction cups on their toes.

“They use it to anchor to a little sand grain so they’re not washed away by the current,” she said. “It was amazing. Microscopic world.”

It’s that adaptability—surviving across vastly different salinity levels—that is at the core of Leasi’s research.

“How they maintain this salt balance in the body,” she said, “because these animals were found across different levels of salinity from freshwater to hyper-saline conditions.”

Typically, these tiny animals only live for a few weeks. Many are female and reproduce asexually by cloning themselves, but when environmental conditions shift, they adapt in extraordinary ways.

“When the condition changes, they are capable of producing males,” Leasi said. “Males are much, much smaller. They don’t have stomachs. They carry sperm, they fertilize a female, and the product of this sexual reproduction is basically a new genotype.”

Guerry Professor and UC Foundation Professor Hope Klug said the undergraduate students participating in Leasi’s research “are getting this really holistic experience.”

“They’re going out in the field, they’re collecting organisms, they’re coming back, they’re looking at them under microscopes, they’re culturing them,” said Klug, whose focus is evolutionary and behavioral ecology. “In addition to that, they’re doing all this genetics and genomics work, so they’re learning these lab techniques. It’s just an incredible opportunity for these students at this early career stage.”

Two days after returning from North Carolina, Leasi received an email that left her stunned, and it directly ties into the research she has long been conducting.

The message was a congratulatory note: a newly discovered species of gastrotrich—a tiny marine organism—had been named in Leasi’s honor.

The species, Musellifer leasiae, was discovered in deep-sea sediments off the coast of Antarctica. At under half a millimeter long, it’s the first member of its family—Muselliferidae—to be formally documented in the Southern Hemisphere.

“One of the authors of a research paper sent me the email telling me the news,” Leasi said. “It’s definitely an honor. I was shocked. I was grateful.”

As it turns out, this was the third time that a species was named after her. All three species belong to a category known as meiofauna—animals smaller than one millimeter that live in the tiny spaces between sediment grains.

“When she told me about it, I was just blown away,” Klug said, “and then she said, ‘Well, it’s happened two other times.’ I had no idea. She receives these very impressive awards, but she’s just not someone who talks about them.

“I don’t think I know anyone else who’s had a species named after them. It is a really rare thing to happen and it is a really big deal.”

The first species named after Leasi, Proales francescae, was found in the Mediterranean Sea along the Côte d’Azur, France. It belongs to the phylum Rotifera (rotifer).

The second species, Typhlopolycystis leasiae, belongs to the phylum Platyhelminthes (flatworms). It was discovered along the Pacific coast of Panama.

“I’m attached to this group of animals (Musellifer) because it was the focal animal group of my Ph.D.,” Leasi said. “They all live in the deep sea. They’re pretty rare to find. So it’s quite an honor to be named.”

She said the thrill of discovery never wears off.

“For me, it is definitely amazing,” Leasi said. “But in general, I get overly excited to see something that was previously discovered but I had never seen before.”

Leasi hopes that the recognition of Musellifer leasiae and the finding of new species will inspire greater interest in the microscopic world.

“I’m hoping that the new generations of scientists can have the patience and the curiosity to approach animals that might not seem so charismatic at first glance,” she said. “But if they have the patience to actually look at these animals under the microscope and understand the diversity, I think it can be a very, very cool job.”

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