Former Royster fellow links plasticity and persistence
Research by Emily Harmon ’24 (PhD) may finally prove an 1890s evolutionary theory about how species “buy time” to avoid extinction.
In the temporary ponds of the desert Southwest, the same spadefoot toad tadpole can become one of two very different animals. Those that eat pond gunk develop as ordinary tadpoles. Those that eat fairy shrimp grow larger, develop bulging jaw muscles and turn cannibalistic. The extra protein helps them develop fast before the pond dries up.
That capacity, the ability of an organism to change its traits in response to its environment within a single lifetime, is called phenotypic plasticity. It is the subject Emily Harmon ’24 (PhD) has spent her career studying. She may have just found the first direct experimental evidence for how it reduces extinction risk and gives evolution a foothold.
“There is a really interesting dynamic system, where different strategies are favored in different environments,” she said.
Harmon earned her doctorate in biology from Carolina in 2024. An alumna of the prestigious Royster Society of Fellows, she is now a postdoctoral researcher at Duke University on a National Science Foundation fellowship.
She began studying the spadefoot toads in the lab of David Pfennig, professor in the UNC College of Arts and Sciences’ biology department, doing fieldwork at the Southwestern Research Station in Portal, Arizona.
Spadefoot toads can change their traits within a single lifetime, an phenomenon called phenotypic plasticity. (Andrew Russell/UNC Research)
When COVID-19 cut off field access, Harmon shifted to studying rotifers, a microscopic freshwater zooplankton that completes a generation in a single day. That speed made it possible to test the “buying time hypothesis,” a theory dating to the 1890s holding that organisms able to adjust their traits in a new environment are more likely to survive long enough for evolution to take hold.
Her results, currently under review, showed that rotifer populations expressing more plasticity in novel environments were more likely to persist and to evolve. “As far as we know, this is the first time this link between plasticity and persistence has been directly, empirically shown,” Harmon said. “We’re ground-truthing this long-standing evolutionary theory.”
The findings matter beyond the lab. As oceans warm and habitats shift, conservation researchers are working to identify which species can adapt and which cannot. Harmon believes plasticity needs to be part of that calculation.
Some of that work is already underway. Researchers are exploring whether corals exposed to heat stress become more resilient to warmer water. If so, those corals and their descendants might have a better chance of surviving in warming oceans.
Harmon hopes her research helps build the scientific foundation for efforts like that. “My end goal is to keep building evidence for how plasticity shapes evolution,” she said. “If we understand how it helps populations survive in new environments, we can reduce their risk of extinction.”
Harmon, who is also an oboist, made a creative adjustment of her own during her spadefoot toad research in the desert. In the downtime waiting for the rain that causes the toads to emerge, Harmon conceived a children’s orchestral piece modeled on Sergei Prokofiev’s “Peter and the Wolf.” The result was “Jack and the Desert Serenade,” a piece in which desert animals each get their own instrumental voice. Her collaboration with a composer led to its 2022 premiere as part of Carolina’s Arts Everywhere Day.
