Students working alongside a stream in a green jungle
By Abe Loomis Photograph by Emma Rogowski ’19

Biologist Ron Bassar and his students study Trinidadian guppies and what they reveal about the natural world.

“What I really like about guppies,” Assistant Professor of Biology Ron Bassar says, “is that they allow us to measure natural selection fairly easily.”

In the rainforests of Trinidad’s northern mountains, where guppies thrive in highland pools, Bassar and his research teams use that fact to their advantage. Armed with nets and Nalgene bottles, they trek through steep terrain to the headwater streams of the Caroní River to capture, mark and release the small, orange-tinted fish. With the guppy populations indexed, scientists and students can examine changes across generations. Waterfalls that isolate fish communities, allowing them to evolve independently from each other, turn the jungle streams into natural laboratories.

This accident of topography forms the foundation of The Guppy Project, a collaboration that began in 2007 among Bassar and professors David Reznick of the University of California, Riverside, Joe Travis of Florida State University, and Tim Coulson of the University of Oxford. Participants study guppies to learn about the genetics of adaptation, the ways that evolution affects ecology and the evolution of coexistence, among other topics.

In July, the project won a three-year, $1.6 million grant from the National Science Foundation to explore the relationship between the guppies and a local rival: a distantly related fish known as Hart’s killifish. Any knowledge researchers can glean about the competitors’—and sometime predators’—effects on each other could have wider implications, Bassar says.

“Removal of top predators, for instance, is a huge problem in aquatic, terrestrial and oceanic ecosystems all over the world,” he says. “Getting rid of sharks in the ocean or sea otters off the coast of California or tigers in India or wolves in North America—what happens in those situations? As scientists, we’re trying to test general principles and rule some out and find evidence for others. And this work in Trinidad gives us the opportunity to do that.”

The Guppy Project also provides opportunities for collaboration with Williams students. Six have participated since Bassar’s arrival on campus in 2017, including Emma Rogowski ’19, who spent the Winter Study of her senior year working with Bassar in Trinidad. Her finding that a parasitic-worm invasion counterintuitively increased the population density of Trinidadian guppies was published last year in the Proceedings of the National Academy of Sciences.

Now studying vaccine-preventable diseases at the Institute for Health Metrics and Evaluation in Seattle, Wash., Rogowski majored in biology with a concentration in public health. Her work on The Guppy Project, she says, perfectly balanced independent study and expert guidance. “I was looking for research that felt more immediately relevant than working in a wet lab, sitting at a bench doing molecular research,” Rogowski says. “I also got great mentorship throughout the process that was both hands-on when it needed to be and let me figure it out for myself when I needed to.”

Rogowski says she is especially appreciative of the understanding she gained by directly participating in data collection for The Guppy Project, which serves her well today.

“Going to the field site, helping catch the fish, hiking the fish back to the cars, driving back to the processing site and helping with the processing to see how, exactly, the data were collected gave me perspective behind the data.”

Bassar says those insights are invaluable to anyone pursuing a career involving research, conservation or the management of wild populations. “Providing the opportunity to have these experiences for Williams College students, and students from the international community, is a central goal of the funded research,” he says.

Abe Loomis, a longtime contributor to Williams Magazine, is an award-winning journalist and songwriter. His writing has appeared in The Wall Street Journal and many other publications.