Associate Professor of Biology Dr. Rachel Penczykowski knew early on that she was drawn to science. Over time, her interest narrowed—first to biology, then ecology. One upper-level parasitology course changed her trajectory. A guest lecture on environmental conditions shaping host–parasite interactions was, as she describes it, a “life-changing light bulb moment.” In that lecture, she realized the intersection of ecology and disease was “exactly what I was most excited about,” she recalls. From then on, disease ecology became her focus.
She pursued a PhD in aquatic disease ecology. When a faculty position opened in the Biology Department at Washington University in St. Louis, it felt like a natural next step. The ecology and evolutionary biology community is highly regarded, but the potential for collaboration at WashU was just as important. She values being at a university large enough for ambitious research across schools, yet small enough that collaboration feels accessible.
Resources such as the Center for the Environment make this possible. Penczykowski attends Center-hosted seminars, workshops, and discussions on grant development. Through these, she has met colleagues in Engineering, Public Health, Earth, Environmental and Planetary Sciences, Statistics, and other departments that intersect with environmental questions. “There’s a low barrier to collaboration,” she explains. “Lots of exciting things are happening, and it’s relatively easy to find people and engage with them.”
At WashU, Dr. Penczykowski’s research builds on and extends her postdoctoral work. Her lab investigates plant–pathogen interactions across geographic regions and climatic zones, asking how environmental variation shapes infection risk, transmission, and evolutionary change. She explains her work by drawing parallels to human disease— Just as scientists track different strains of influenza, her lab studies the genetic diversity of fungal plant pathogens and how that diversity shifts across landscapes and climates.
Even after years of research, moments in the lab still surprise her. In ecology, results rarely unfold as predicted, as natural systems are too complex. That’s why the rare moments when data do confirm a hypothesis stand out. She initially didn’t believe it when a graduate student predicted that there would be greater prevalence of powdery mildew infection in more urban populations of a focal host plant, and that’s exactly what was found two years in a row. “Wait—that’s what we hypothesized would happen,” she recalls thinking. “That doesn’t happen in ecology.” For Penczykowski, moments like these reveal how strongly environmental forces like climate and landscape can shape disease dynamics, emerging clearly despite the many other variables at play.
Plants offer unique advantages for studying disease-related questions. Because they remain fixed in place, the spatial dimensions of disease can be observed and manipulated in ways that are impossible in human populations. Her team can grow plants in pots, move them across environmental gradients, or conduct large-scale greenhouse and garden experiments to test how context influences infection. One focus of her lab is the common roadside plant, plantain, which grows throughout the St. Louis region. Her team identifies populations in environments that vary from cooler, shaded green spaces to warmer urban “heat island” areas, and tracks how frequently those plants become infected with a fungal pathogen known as powdery mildew. In comparing disease patterns across these sites, her lab uncovers why infections often emerge earlier and spread more intensely in urban environments. These kinds of experiments allow researchers to isolate the role of environmental context in shaping disease, revealing how climate and landscape can drive infection dynamics in ways that would be impossible to test in human populations.
By studying hosts and pathogens that have coexisted across different climates, her lab gains insight into how pathogens respond to environmental change and may continue to evolve as climates shift. These insights may inform more sustainable crop management strategies while advancing understanding of disease transmission and evolution across biological systems.