An eye for the beautiful

With a two-year Humboldt Postdoctoral Fellowship, Daniela Perez plans to unlock one of the most elusive—and beautiful—mysteries of nematode behavior

May 02, 2023

When considering the worm C. elegans, you’d be forgiven for assuming that biologists had figured out all there was to know. The infamous darling of lab studies was the first multicellular life form to have its entire genome sequenced, and has been used for over half a century as a classic model for studying everything from sleep to sex to how cells grow, age, and die.

But the tiny test animal hasn’t yet given up all its secrets to science; and this year, MPI-AB postdoc Daniela Perez has won a prestigious Humboldt Fellowship for a project that asks a new question of this old system.

The project, which is a collaboration between Perez and nematode expert Serena Ding, will probe one of the most striking, yet least understood, behaviors in C. elegans: collective towering

“It’s pure curiosity-driven research,” says Ding, who leads the Genes and Behavior Max Planck Research Group. “For years, nematode researchers have known about worms aggregating by the thousands to form towering structures; but we’ve never understood how or why. ”

Working in Ding’s lab located at the University of Konstanz, Perez will deploy a suite of genetic, imaging, and tracking technologies—developed and refined by Ding—to finally picture this collective behavior in vivid detail. Further, Perez will bring her expertise in behavioral evolution to bear on answering the elusive question: why has this behavior evolved at all?

“So much is known about the biology of this worm in the lab,” says Perez, “but this animal also lives in the real world with real challenges it has to solve. I can’t help but wonder why they form towers, and to search for the evolutionary origin of this strange, but beautiful, collective behavior.”

One might say that Perez’s motivation for studying C. elegans is characteristic of her path into science: a wandering tour to explore evolution’s most beautiful sights.

Drawing a path to science

In the 15 years since starting research, Perez has conducted a tour of behavioral evolution. She’s studied mate choice of fiery fiddler crab claws; evolution of bird nest architecture; diversity of insect coloration; and lekking behavior in extravagant bird species, such as rainbow-hued manakins and birds of paradise. By her own admission, her portfolio is eclectic. “My interests don’t fit neatly into one label,” says the scientist. “Except, maybe, that all my study subjects are visually beautiful.”

The aesthetic sense makes perfect sense when set against Perez’s background. As well as being a biologist, Perez is a visual artist. Her photorealistic drawings depict plants and animals in astonishing detail. Her “insane perfectionism,” she says, goes hand-in-hand with being a scientist. “I’ve always been observant; always interested in detail.”

As a child growing up in urban Brazil, she spent hours toying with ant trails on the pavement outside her apartment block, captivated by the movements and patterns that unfurled. This devotion to detail provided the perfect training for university studies in biology, which eventually took her out of Brazil to a PhD position in Australia.

There, she studied sexual selection in fiddler crabs—a group of species in which males grow a large, bright claw that they wave in the air to catch the attention of females. Perez would end up spending seven years on the system, becoming fascinated by the way males would wave their claws in synchrony.

“It was so puzzling to see hundreds of males, all fierce competitors, waving their arms together as if on the same team,” she laughs. By deploying robotic male crabs, Perez eventually unearthed an answer to this evolutionary mystery—but her curiosity with synchronicity was far from satisfied.

In 2020, when Ding advertised a postdoctoral position to investigate a novel collective behavior in C. elegans, Perez took notice—and was on the way to the MPI-AB in Konstanz.

“Nobody knows for sure why they do it”

On its own, C. elegans is a microscopic worm measuring only 1 millimeter long that spends its life buried in soil or rotting vegetation. But when environmental factors align, the tiny animals will aggregate and climb on top of each other to form towers tall enough to be seen with the naked eye.

“When you talk about towering to anybody in the C. elegans field, people know about it, are excited by it, but don’t know anything about it,” says Ding.

There’s a simple reason the seemingly-simple question remains unanswered. “It’s really hard to get the worms to tower in the lab,” says Ding. “People have observed the towering behavior on natural substrates brought into the lab from the wild, but they haven’t found a way to induce towering so we can study them with experimental control. Because the worms are so tiny, they’re impossible to study directly in the wild.”

But during her postdoc, Ding made a breakthrough. After some trial-and-error tests she did “for a side project,” Ding discovered that worms will form towers in the lab if two conditions are met. “They need a vertical structure to climb and something that stresses them out.”

Fast forward three years and Perez has refined Ding’s technique, allowing her to trigger the worms to tower on command. With that pipeline in place, the stage is set for Perez to shine light on to this dark corner of C. elegans biology.  “It’s such an exciting time to be studying this because we can use techniques that are now available for quantifying behavior,” says Perez.

What does collective nematode towering look like in the lab?

Perez films adult worms aggregating to form a “flame-type” tower.

Perez will draw on fluorescent labelling and imaging techniques, as well as automated tracking, to study the individual worms of the tower. “We can label different worms in different colors and so can distinguish individuals in the collective,” she says. “This will show us how worms are moving in the tower, who is at the top, who is joining, and who is leaving.”

Knowing the “who” is particularly important for answering the evolutionary question of why towers form. In evolution, after all, the winners take all.

“People think that towering could benefit worms by allowing them to reach passing insects, which they climb on to hitchhike to more fruitful places,” says Perez. “But only worms at the top of the tower catch a ride, and so who makes it to the top and who doesn’t is a question that matters a lot.”

Through naturalistic experiments, Perez will probe questions of adaptation, cooperation and competition, teasing apart the ecological and evolutionary drivers of towering.

For Ding, the answers have been a long time coming.

“We know that many nematode species display this towering behavior. It’s probably super important in the life history of an entire phylum, but nobody knows for sure why they do it.”

“With Daniela’s skills in behavioral ecology and evolution, combined with the deep knowledge that exists on C. elegans molecular biology, we have a powerful synergy that will enable us to not only get to the how, but also to the why, of this fascinating phenomenon.”

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