When most people hear about a fishing expedition in Mexico’s Yucatán Peninsula, they might picture researchers snorkeling through coral reefs in the Caribbean Sea or diving into crystal-clear cenotes, surrounded by postcard-perfect scenery.
But nothing I had imagined—or Googled—before my first field trip came close to the reality we faced in our search for pupfishes. We were after something far more elusive: the Laguna Chichancanab adaptive radiation, a group of pupfish species named for the way their tails wag like those of playful puppies. These fish exhibit remarkably different head shapes, a clue to their fascinating evolutionary story.
Tucked deep in the Yucatán and known to the ancient Maya as the “Little Sea,” Laguna Chichancanab is a 12-square-mile, landlocked lake. It’s home to one of only two known examples of pupfish adaptive radiations occurring in sympatry—a term biologists use when multiple species evolve and live together in the same habitat. Once described as five distinct species just four decades ago, the Chichancanab pupfishes rapidly evolved over less than 8,000 years, developing specialized feeding behaviors, and striking craniofacial differences to avoid competing for the same food.
The team
The Fish Speciation lab at the Department of Integrative Biology and the Museum of Vertebrate Zoology at UC Berkeley directed by Dr. Christopher H. Martin studies the ecology, evolution, development, and genomics of fish adaptive radiations. To do this, the team uses microendemic radiations of trophic (or dietary) specialist pupfish found only on San Salvador Island, Bahamas, and in Laguna Chichancanab, Mexico.
As a postdoctoral fellow in his lab, I study the genetic changes underlying the development of craniofacial divergence during embryonic and larval development in Bahamian pupfishes. This work is an effort to identify novel genes and gene variants involved in adaptive craniofacial morphologies and their potential implications for understanding clinical craniofacial variation in humans.
In 2022, Martin and his collaborators from Universidad Nacional Autónoma de México (UNAM) and UC Riverside traveled to Laguna Chichancanab to establish local collaborations and estimate the diversity and number of pupfishes in the lake.
They explored several sites along the southern edge of the lagoon and successfully found three of the five originally described pupfish species: C. beltrani, the generalist of the group; C. labiosus, a carnivorous pupfish with thick, fleshy lips; and C. simus, known as the “boxer pupfish” for its distinctive jaw, which juts out at a sharp angle—similar to the scale-eating pupfish C. desquamator found in San Salvador Island.
But their discoveries came with a sobering reality. The numbers of these rare fish were lower than ever, continuing a troubling trend of decline and extinction likely driven by pollution and the introduction of invasive species like the Mayan cichlid (Mayaheros) and Mozambique tilapia (Oreochromis mossambicus).
While the 2022 field expedition was relatively successful, I can’t say the same about our fieldwork in 2024. Described less than a century ago, the Chichancanab pupfish radiation is becoming a poignant symbol of the ongoing loss of animal diversity across the globe in the Anthropocene.